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Seagrass habitats play a major role in fisheries productivity through nursery functions and feeding grounds for diverse fish species. However, little is known about the seasonal distribution of fish larvae at large spatial scales in coastal East Africa. We investigated drivers of the seasonal fish larvae abundance and composition in seagrass habitats in Kenya and Tanzania. We found a high diversity of fish larvae (54 families) inhabiting seagrass habitats that differed between sites and seasons. Fish larvae abundance were highest in Kenya, particularly during the northeast monsoon season. Overall, total larval abundances per site were low, reaching less than 190 individuals/100 m3 in Kenya and less than 40 individuals/100 m3 in Tanzania, likely related to the low productivity and strong hydrodynamic processes in this region. Our data suggests that most of the fish spawn year-round in these tropical waters as we did not find strong seasonal patterns. All sites had a high relative abundance of larvae from demersal spawning fishes, indicating that many fish species move to coastal sites for spawning. Primary productivity and dissolved oxygen, driven by hydrodynamics conditions are positively related to fish larvae productivity both in Kenya and Tanzania. These findings indicate that the occurrence of both resident and transient fish larvae in seagrass meadows is driven by strong hydrodynamic and tidal processes that transport fish larvae across adjacent habitats. [ABSTRACT FROM AUTHOR]

Understanding the molecular mechanisms underlying individual responses to environmental changes is crucial for species conservation and management. Pelagic fishes including Atlantic herring (Clupea harengus) are of particular interest because of their key ecological and economic roles and their susceptibility to a changing ocean from global warming. Temperature and photoperiod have been linked with spawning time and location in adult herring, but no study has thus far investigated the role of environmental factors on gene regulation during the vulnerable early developmental stages. Here, we examine DNA methylation patterns of larval herring bred under two temperatures (11°C and 13°C) and photoperiod (6 and 12 h) regimes in a 2 × 2 factorial design. We found consistently high levels of global methylation across all individuals and a decline in global methylation with increased developmental stage that was more pronounced at 13°C (p ≤ 0.007) than at 11°C (p ≥ 0.21). Most of the differentially methylated sites were in exon and promoter regions for genes linked to metabolism and development, some of which were hypermethylated at higher temperature. These results demonstrate the important role of DNA methylation during larval development and suggest that this molecular mechanism might be key in regulating early‐stage responses to environmental stressors in Atlantic herring. [ABSTRACT FROM AUTHOR]

Simple Summary: This study describes the composition, abundance, spatial distribution and differences in day/night vertical distribution of ichthyoplankton in the southern Adriatic Sea. Samples were collected from 9 to 18 May 2013, in multiple layers from near the seabed to the surface by the electronic multinet EZ-NET BIONESS (Bedford Institute of Oceanography Net Environmental Sampling System). A total of 20 species, belonging to 20 genera and 13 families, were identified. The community was dominated by Gonostomatidae, followed by Engraulidae, Myctophidae and Photychthaidae. The most abundant species was Cyclothone braueri, followed by Engraulis encrasicolus, Ceratoscopelus maderensis, Cyclothone pygmaea, Vinciguerria attenuata and Myctophum punctatum. An inshore/offshore increasing gradient in biodiversity and abundance was observed. Different weighted mean depths (WMD) were observed for larvae and juveniles. No diel vertical migrations were observed. The high abundance of meso-bathypelagic species in the upper 100 m confirms the epipelagic zone as an important environment for the development of the larval stages of these fish. Studies based on fish early life stages can provide information on spawning grounds and nursery areas, helping to determine the implications for stock biomass fluctuations of recruitment variability. This study describes the composition, abundance, spatial distribution and differences in day/night vertical distribution of ichthyoplankton in the southern Adriatic Sea. Samples were collected within the framework of the COCONET project (Towards COast to COast NETworks of marine protected areas) from 9 to 18 May 2013 by the R/V Urania, using the electronic multinet EZ-NET BIONESS (Bedford Institute of Oceanography Net Environmental Sampling System). A total of 20 species, belonging to 20 genera and 13 families, were identified. Of the collected larvae, 74.3% were meso- or bathypelagic species, 24.7% were epipelagic and 0.9% were demersal. The community was dominated by Gonostomatidae, followed by Engraulidae, Myctophidae and Photychthaidae. The most abundant species was Cyclothone braueri (45.6%), followed by Engraulis encrasicolus, Ceratoscopelus maderensis, Cyclothone pygmaea, Vinciguerria attenuata and Myctophum punctatum. An inshore/offshore increasing gradient in biodiversity and abundance was observed. Different weighted mean depths (WMDs) were observed for larvae and juveniles. No diel vertical migrations were observed. The high abundance of meso- or bathypelagic species in the upper 100 m confirms the epipelagic zone as an important environment for the development of the larval stages of these fish. [ABSTRACT FROM AUTHOR]

Spawning sites play a key role in the reproduction of fish allowing populations to endure over time. The Nechí River is an important spawning area for potamodromous fish species where one of the threats is dam construction. In order to determine the importance of the Nechí River as a spawning site in the Magdalena River basin, sampling was conducted during the low-water-to-high-water season transition period between 2018 and 2019 at seven sampling sites. The average density of ichthyoplankton was 42.4 ind.10m-3 (SD = 7.1). Of the individuals in the post-larval stage, seven migratory species were identified, and two additional taxa were identified to genus; Prochilodus magdalenae, Megaleporinus muyscorum, and Pseudoplatystoma magdaleniatum presented the greatest density. At the temporal level, the greatest density of larvae of potamodromous species was observed in the first high-water season of 2019 with a total of 5.7 ind.10m-3(SD = 1.044), of which the most representative at the seasonal level were the Cauca River, Magdalena River, and Nechí River before it flows into the Cauca River. There were significant differences in the frequency of embryos and vitelline larvae of the potamodromous species in the interaction of the sampling sites and high-water seasons, as well as with the density of post-larvae. The average drift distance of the spawning areas is roughly 52.1 km. A positive association was found between the volume of turbined water and the presence of ichthyoplankton in the Porce River site, after discharge from the Porce III Hydroelectric Plant. The Nechí River is an important spawning site and there seems to be an association between the increase in ichthyoplankton densities and the distance to the dam (Porce III) as long as there are floodplains along the course of the river. [ABSTRACT FROM AUTHOR]

In South America, knowledge of major spawning sites is crucial for maintaining migratory fish populations. In this study, we aimed to understand the spatio-temporal distribution of fish eggs in the upper São Francisco River using high sampling frequency and DNA metabarcoding identification. We evaluated the possible effects of the non-molecular identification of eggs and decreased sampling frequency on the determination of spawning sites and major breeding periods. Collections were carried out every three days from November 2019 to February 2020. We found that, if we had assumed that all of the free and non-adhesive sampled eggs belonged to migratory species, as is usual in the literature, this assumption would have been wrong for both the spawning sites and the breeding periods. Moreover, any decrease in the frequency of sampling could dramatically affect the determination of the major spawning rivers, and the spawning events of some of the migratory species may not have been detected. Therefore, without the proper identification and adequate sampling frequency of eggs, important spawning sites may be overlooked, leading to ineffective or inappropriate conservation measures. [ABSTRACT FROM AUTHOR]

This work aims to describe the larval stages and the seasonal variation in the abundance of three mesopelagic species whose larvae are surprisingly abundant near coral reef areas in the Red Sea. The larvae were collected monthly using a plankton net (500 µ) from three coastal coral reef areas surrounding Sharm El-Sheikh on the Egyptian Red Sea coast between January and December 2015. The identification of larvae was based on the morphological and meristic characteristics according to the available literature. The larvae of this species were divided into preflexion, flexion, and postflexion stages and they were also categorized according to their size into relevant size classes. Mesopelagic fishes were represented in the collection by four species belonging to four families: Vinciguerria mabahiss (Family: Phosichthyidae), Benthosema pterotum (Family: Myctophidae), Astronesthes martensii (Family: Stomiidae; subfamily: Astronesthinae), and Trichiurus sp. (Family: Trichiuridae). In general, a total of 3678 larvae were collected, of which 1191, constituting about 32% of the total fish larvae, belonged to mesopelagic species. The most abundant species was V. mabahiss, with 677 larvae that constituted 18% and 57% of the total larvae and mesopelagic fish larvae, respectively. The second most abundant species was B. pterotum, which was represented by 485 larvae (13% of the total larvae and 40% of the mesopelagic fish larvae). A. martensii was represented by the lowest number of larvae (29 larvae, 2%). Most larvae of the three species were small and in the preflexion stage, whereas larger larvae are absent. They are highly abundant in the cooler months of the year between November and April. The high number of preflexion larvae may indicate that the three mesopelagic species spawn in the colder times of the year. [ABSTRACT FROM AUTHOR]

Fall is an important time of year for fish recruitment in the Gulf of Mexico, with many commercially and recreationally important species spawning during this period. Changes in temperature and salinity regimes through seasonally abnormal freshwater input may change spawning patterns and displace larvae. Such an event occurred off the coast of Galveston Bay, Texas, when a freshwater flood plume formed from unprecedented rainfall related to Hurricane Harvey at the end of August 2017. This study investigated the effects of a large‐scale flood plume on larval fish assemblages, collected at nearshore and shelf zones 1 and 2 months after Hurricane Harvey. Samples from 2017 were compared to historical datasets collected by NOAA Fisheries in September (2000–2004 and 2006–2016) and October (2000–2012). Evidence of lowered water temperature and salinity was found in both September and October 2017. Larval community composition changed along cross‐shelf gradients and with increasing distance from shore. We also found evidence of 2017 assemblages differing from historical data, with the September 2017 assemblage more closely resembling those from October historical samples. Observed differences in 2017 assemblages were most likely explained by an earlier onset in fall sciaenid spawning, suggesting that decreases in water temperature occurring during hurricanes have the potential to alter fish spawning patterns. [ABSTRACT FROM AUTHOR]

The notothenioid family Bathydraconidae is a poorly understood family of fishes endemic to the Southern Ocean. There is especially little information on Akarotaxis nudiceps, one of the deepest‐dwelling and least fecund bathydraconid species. Using genetic and morphological data, we document and describe the larval stages of this unique species, offer a novel characteristic to distinguish it from the morphologically similar bathydraconid Prionodraco evansii and use the sampling locations to infer a possible spawning area of A. nudiceps along the western Antarctic Peninsula. These results provide important baseline information for locating, identifying and studying the biology of A. nudiceps, an important component of the Southern Ocean ecosystem. [ABSTRACT FROM AUTHOR]

Abundance indices are essential data for the application of stock assessment models to obtain fish abundance estimates. Abundance indices have usually been derived from fishery-dependent data, yet the increase in fisheries-independent surveys is now offering new opportunities for these calculations. In this study, we explored the usefulness of ichthyoplankton indices derived from scientific surveys in estimating spawning biomass. In addition, we also investigated whether the strength of the year–class of the commercial cohort of Atlantic hake, as a determinant, could be defined at an early life stage. We used samples collected during the triennial mackerel and horse mackerel egg surveys (MEGS), which cover the hake spawning area in the Bay of Biscay. The biomass indices were determined as the abundance of eggs in the early development stage (stage 1) when transformed into egg production (EP) from 1995 to 2019 in the months of March and April—which is considered a period of high spawning activity for hake in this area. Additionally, we built a metric for larval abundance and converted larval length into age. This was in addition to constructing a pre-recruit year-class index (YCI) while using the EVHOE bottom trawl abundance database for hake for the period of 1997 to 2016. The results of regression analysis of egg production and spawning stock biomass indicate that both parameters are significantly correlated (r = 0.76). By connecting the abundance of eggs and larvae in the adjoining stages, we are able to identify two periods of high mortality associated with the transition from "yolk-sac-first" to "feeding larvae" and "late larvae-YCI10", but we were unable to discover when the strength of the recruitment year–class is determined. As such, it appears that for the northern stock of hake, recruitment is established in the late juvenile stages. [ABSTRACT FROM AUTHOR]

Simple Summary: Due to the high mortality of fish in the early stages of ontogenesis, the detection of factors affecting it seems to be an extremely important problem. We investigated intra-decadal dynamics and spatial distribution of the ichthyoplankton abundance that depends on hydrometeorological factors. We focused on Sevastopol Bay and its four areas. The ichthyoplankton distribution by areas of Sevastopol Bay was associated with the peculiarities of the pollution distribution and with the wind regime. For the first time, a positive effect of temperature and repeatability of northern and northeastern winds on the ichthyoplankton number during the summer spawning in all areas was reported. The abundance of ichthyoplankton is influenced by several factors: (a) In the southern area, a positive influence of temperature and northerly winds on the ichthyoplankton abundance was confirmed. (b) In the eastern area, the discharge of rivers is an additional factor. (c) Characteristics of winds in western and central areas are significantly impacted by the orography peculiarities. The data obtained during the research highlighted the importance of comprehensive monitoring studies using an intra-decadal approach on scrutinizing ichthyoplankton abundance, distribution and many other characteristics. High mortality of fish in the early stages of ontogenesis requires the detection of factors affecting it and is an extremely important problem. For this reason, we tried to consider the influence of some hydrometeorological factors on the intra-decadal dynamics and spatial distribution of ichthyoplankton abundance in Sevastopol Bay. To this end, we analyzed ichthyoplankton samples collected in 2012–2021 in Sevastopol Bay, and the four districts were identified. The ichthyoplankton distribution by areas was associated with the peculiarities of the pollution distribution. The maximum numbers in eggs (34.7 ± 7.5 ind. m−2) and larvae (10.0 ± 2.4 ind. m−2) were recorded in July–August. For the first time, a positive effect of temperature and repeatability of north and northeast winds on the ichthyoplankton number during the summer spawning in all identified areas of Sevastopol Bay using principal component analysis (PCA) was reported. In the southern region, positive influence of temperature and northerly winds on the ichthyoplankton abundance was confirmed by ANOVA (p = 0.02), and Pearson's correlation analysis revealed significant correlations between these parameters on inter-annual scale (r > 0.5). In the eastern area, the discharge of rivers is an additional factor affecting the abundance of ichthyoplankton, while in the western and central areas, these factors were the wind characteristics caused by the orography peculiarities. The pollution spread in Sevastopol Bay is also largely due to the wind regime. The importance of comprehensive monitoring studies using intra-decadal data on ichthyoplankton is emphasized. [ABSTRACT FROM AUTHOR]

The species structure and spatial distribution of ichthyoplankton in July–August 2019 during the period of mass spawning of warm-water fish species are presented. The material was collected at the shelf and in the deep waters of the Black Sea off the Crimean Peninsula and along the Caucasian coast. In ichthyoplankton, eggs and larvae of 29 species of fish from 19 families were identified. The indices of species richness in the open sea and in the coastal areas were similar. European anchovy Engraulis encrasicolus (Linnaeus, 1758) dominated in ichthyoplankton, its maximum egg abundance reached 260 ind./m2, larvae abundance, 117 ind./m2. The highest spawning efficiency of E. encrasicolus was observed in coastal waters heated up to 26–27°C near the Caucasian coast and on the western shelf of the Crimean Peninsula, where the ratio of the number of larvae to the number of eggs was 30% in the samples. An increased population density of ichthyoplankton was also noted within the Crimean anticyclonic gyre, the shelf thermodynamic formation most stable in time. We assume that favorable conditions were formed there for spawning and survival of fish at the early stages of development. [ABSTRACT FROM AUTHOR]

Despite their broad distribution across the North Pacific Ocean, the only known spawning grounds for Pacific Bluefin Tuna (Thunnus orientalis) are around coastal Japan and the East China Sea. However, an increase in the prevalence of large bluefin tuna up to 10 years old in the California Current System during exceptionally warm ocean conditions has led to speculation that they may be spawning in this region. To investigate this possibility, we collected samples from 36 females (estimated 3–8 years old) between 2015 and 2019. Histological analyses revealed no signs of imminent, active, or recent spawning. Further examination of historical ichthyoplankton collections showed no records of larval bluefin tuna, but confirmed the presence of the larvae of other tuna species in waters > 24°C. Fishery-dependent records showed that bluefin tuna are rarely recorded in purse seine catches where surface temperatures exceed 23°C. Our study, therefore, provided no evidence of bluefin tuna reproduction in the CCS. However, more comprehensive sampling, in particular off southern Baja California, may be required to confirm the absence of spawning. [ABSTRACT FROM AUTHOR]

The 2014–2016 Northeast Pacific marine heatwave (MHW) induced the warmest 3‐year period on record in the California Current Ecosystem. We tested whether larval fish assemblage structure, phenology, and diversity dynamics were comparable to past warming events from 1951 to 2013. First, we hypothesized, based on past observations of biological effect of warming, that mesopelagic species with southern distributions relative to southern California and Pacific sardine Sardinops sagax (a coastal pelagic species) would increase during the MHW while northern mesopelagics and northern anchovy Engraulis mordax (coastal pelagic) abundances would decline. Similar to past warming, southern mesopelagics increased and northern mesopelagics decreased. Unexpectedly, however, a common southern mesopelagic, Mexican lampfish Triphoturus mexicanus, was approximately three times more abundant than the previous annual high. Furthermore, whereas sardine abundance did not increase, larval anchovy abundance rose to near‐record highs in summer 2016. Second, we hypothesized that fishes would spawn earlier during the MHW. Fishes did not spawn in an earlier season within a year, but five of six southern mesopelagic taxa spawned earlier than typical within winter and spring. Third, we predicted that species richness would increase moderately due to an influx of southern and exodus of northern species. Richness, however, was very high in all seasons and the highest ever during the summer as multiple species with primarily southern distributions were recorded spawning for the first time in southern California. The richness of northern species was also unexpectedly high during the MHW. Northern species likely persisted in the study area because in addition to the warm water, pockets of cold water were consistently present. If, as predicted, conditions similar to the MHW become more common as oceans warm, this unique and largely unexpected combination of fishes may reflect future biological conditions. [ABSTRACT FROM AUTHOR]

Since 1850, each successive decade has been warmer than any preceding one. Warming could make a major contribution to the growth of fish larvae. To evaluate the influence of water temperature on the growth of larvae who spawned in later spring and early summer, we selected Scomberomorus niphonius, which has important ecological and economic value as a sample fish species. We conducted highresolution spatiotemporal surveys during the 2015 spawning season at an important spawning ground in China. We found that the temperature required for larval survival was stricter than that for spawning. Within the appropriate temperature range, a rapid rise in water temperature was favourable for larval hatching, but S. niphonius hatched at relatively low temperature exhibited a faster growth rate in the yolk-sac and pre-flexion stages. The accumulated temperature and hatching temperature significantly affected the growth rate of S. niphonius larvae. The model that considered developmental stages provided a better explanation of the data than the model that only considered the temperature effect. The model improvement in terms of variance explained was higher for the early developmental stages than for the later developmental stages, suggesting that stage-specific temperature influences were prominent in the earlier stages, like the yolk-sac stage, and then reduced. Our results implied that water temperature anomalies could be hazardous to fish larvae, especially for fish spawning in late spring and early summer. Given that early-life stage fish are highly sensitive to water temperature, it is imperative to incorporate the potential effects of climate change into fisheries management. [ABSTRACT FROM AUTHOR]

Multiyear periods of relatively cold temperatures (2007–2013) and warm temperatures (2001–2005 and 2014–2018) altered the eastern Bering Sea ecosystem, affecting ocean currents and wind patterns, plankton community, and spatial distribution of fishes. Yellowfin sole Limanda aspera larvae were collected from the inner domain (≤50 m depth) of the eastern Bering Sea among four warm years (2002, 2004, 2005, 2016), an average year (2006), and three cold years (2007, 2010, 2012). Spatial distribution and density of larvae among those years was analyzed using generalized additive models that included timing of sea‐ice retreat, areal coverage of water ≤0°C, and water temperature as covariates. Analyses indicated a combination of temperature effects on the location and timing of spawning, and on egg and larval survival, may explain the variation in larval density and distribution among years. During warm years, higher density and wider spatial distribution of larvae may be due to earlier spawning, an expansion of the spawning area, and higher egg and larvae survival due to favorable temperatures. Larval distribution contracted shoreward, and density was lower during cold conditions and was likely due to fish spawning closer to shore to remain in preferred temperatures, later spawning, and increased mortality. Predicted drift trajectories from spawning areas showed that larvae would reach nursery grounds in most years. Years when the drift period was longer than the pelagic phase of the larvae occurred during both warm and cold conditions indicating that settlement outside of nursery areas could happen during either temperature condition. [ABSTRACT FROM AUTHOR]

Setting ecologically based water‐extraction rules requires an understanding of the relationships between hydrology and the completion of aquatic organism life cycles. Successful reproduction of riverine fishes has been linked to hydrological variation across diverse climatic regions. However, the reproductive ecology for many species in wet–dry tropical northern Australia is poorly understood, and consequently there is little knowledge on how temporal (seasonal) and spatial hydrological variation influences fish reproduction in this region.This study aimed to quantify the hydrology‐related reproductive ecologies of freshwater fish across the wet–dry seasonal cycle and between differing hydrological classes in a northern Australian river (Daly River, Northern Territory) subject to increasing interest in water extraction. Sampling of larval and juvenile fish was undertaken over 1 year at eight sites classified into perennial and intermittent flow types. Fish spawning phenologies were developed and spatial–temporal dynamics in larval fish assemblages were investigated using model‐based multivariate and univariate analyses.Spawning occurred in all hydrological seasons, with low‐flow dry season periods identified as important for many fish taxa. For a different fish assemblage, spawning mostly occurred during high‐flow wet season periods. Larval assemblages in the wet season were more diverse than in the dry and wet–dry seasons. Perennial sites maintained higher diversity than intermittent sites year‐round; however, larvae were more abundant in intermittent sites for some taxa. Spatial and temporal differences in larval assemblages were largely explained by variation in the occurrence and relative abundance of three aseasonally spawning taxa (Craterocephalus spp., Melanotaenia spp. and Ambassis spp.) and the largely wet‐period spawning of Terapontidae spp.These results add to growing evidence of variation in spawning phenologies among fish species and the use of multiple hydrological phases for aseasonal reproduction. The diverse range of hydrological conditions used for spawning and rearing, and the differences between hydrological river classes among taxa, suggests that water‐extraction and environmental flow rules should aim to maintain hydrological conditions catchment‐wide during both low and high‐flow periods to reduce the risk of impacting fish reproduction. In particular, the results suggest that if perennially flowing sites began to flow intermittently, such as through over‐extraction of water or due to climate change, less diverse fish assemblages may result.This study expands our understanding of the relationships between hydrology and the reproductive ecology of freshwater fish in wet–dry tropical climates and may inform future ecologically based approaches to setting water‐extraction rules. [ABSTRACT FROM AUTHOR]

Fish larval drift is an essential step in the life cycle of riverine fish species as it determines dispersal and colonisation. Anthropogenic flow alterations and interruption of longitudinal and lateral connectivity by river damming and straightening can severely affect larval drift patterns. In this study, we characterised spatio‐temporal drift patterns of fish larvae in the heavily regulated large alpine River Inn and within a constructed nature‐like fish bypass.Drift was investigated in the main reproduction period of the fish fauna in this river, ranging from mid‐April to end of June. Diel patterns were assessed by samples taken during day, dusk, night, and dawn each day of sampling. To obtain robust species identification, we used DNA barcoding for genetic verification of phenotypically pre‐sorted groups.From a total of 1,069 fish larvae and 283 fish eggs caught, DNA barcoding revealed 16 species from five families, including several target species of conservation. We found strong evidence that several endangered species, such as Chondrostoma nasus, Thymallus thymallus, Cottus gobio, and Aspius aspius successfully reproduced in the bypass system. Genetic species verification showed a high level of homogeneity in most phenotypically pre‐sorted groups.Distinct seasonal patterns were observed, with the majority of fish species in the drift observed in mid‐June. Thymallus thymallus and Cottus gobio dominated larval drift at the beginning of the observation followed by mainly unimodal abundance peaks of several Cyprinid species. Nocturnal drift prevailed in all species.Our results on the spatial occurrence and abundances of fish larvae highlight the importance of bypass systems in heavily modified waterbodies to provide valuable spawning habitats and drift corridors around dams. Moreover, the distinct species‐specific time patterns of larval drift represent a first basis to direct future discharge and river management plans in large alpine rivers towards a protection of the sensitive larval stages of specific target species of conservation. This includes bypass and turbine operation modes in the period of highest drift activity, as well as the construction of nature‐like bypass systems and creation of spawning grounds therein. [ABSTRACT FROM AUTHOR]

The ontogeny of Ilisha elongata was reviewed, and their early distribution was examined because information on the early life history of this species is limited. Revision in ontogeny revealed several unique characteristics to this species, such as two chorions in the egg and a more anterior pelvic bud (fin) position. These characteristics contrast strikingly with the clupeid fishes, suggesting that this species belongs to the Pristigasteridae and not to the Clupeidae. Data from ichthyoplankton collected in March, May, July and November suggest that I. elongata spawned just off river mouths in summer and attained peak spawning in June. The larvae with elliptical eyes migrated inside the rivers, where the waters were more turbid. Thus, the spawning and nursery grounds of I. elongata almost entirely overlapped with those of the clupeid Sardinella zunasi both temporally and spatially, which may result in larval competition between the two species. [ABSTRACT FROM AUTHOR]

Systematic larval fish surveys increase the probability of detecting rare species and provide ecological insights for more common species that can be difficult to infer from surveys of older life-stages. To characterize the reproductive success of the extant fish assemblage in the western Grand Canyon portion of the Colorado River, we conducted systematic larval fish surveys in 2014 and 2015. The effort identified endangered razorback sucker (Xyrauchen texanus) as initiating spawning in February with a continuation through July. We collected recently hatched protolarval fish throughout the study area including the most upstream sample sites, suggesting fish spawned throughout and upstream of the study area. Our collection of a protolarval endangered humpback chub (Gila cypha) supports the hypothesis that the population increased in range within the Grand Canyon from its dramatic 2001 contraction into the Little Colorado River and suggests localized spawning. Back-calculating hatching dates indicated humpback chub began hatching in late April and continued through mid-May. Native fishes numerically dominated larval fish collections (97.6 and 99.3% for 2014 and 2015, respectively) and recruitment to the early juvenile life-stage was documented for all fish species captured except razorback sucker. Abundance, measured as catch per unit effort and frequency of occurrence, was different between years for each native species captured (n = 5). Interannual differences in abiotic factors (discharge, diel fluctuations in discharge, and water temperature) were significantly different for most months between years. A redundancy analysis, evaluating the relationship between abiotic environmental factors and catch rates, suggested both discharge and water temperature were associated with speckled dace (Rhinichthys osculus), bluehead sucker (Catostomus discobolus), and flannelmouth sucker (Catostomus latipinnis), with a positive correlation to water temperature and a negative correlation to discharge. We were unable to identify associations between abiotic factors and the endangered fishes, which may have been due to the lack of variability in those species’ catch rates. Improving our understanding of the relationship between reproductive success and abiotic factors would enhance management of the system to benefit native fishes. [ABSTRACT FROM AUTHOR]

Discus fish (Symphysodon aequifasciatus) exhibit a unique parental care behavior: adult discus produces secretion through their skin, on which the larvae live after birth. The immune components in the skin mucus of parental discus would change during different parental care. C-type lectins (CTLs) could identify and eliminate pathogenic microorganisms and play important roles in innate immunity. Studies on CTLs of discus fish especially during parental care, however, are scarce. Here, we identified 186 CTL genes that distributed in 27 linkage groups based on discus genome. Phylogenetic analysis showed that S. aequifasciatus CTL (SaCTL) members were grouped into 14 subfamilies. A total of 80 gene replication events occurred, of which 15 pairs were subjected to segmental duplication and 65 pairs underwent tandem duplication. Ka/Ks ranged from 0.11 (SaCTL25 / SaCTL158) to 0.68 (SaCTL36 / SaCTL69), all undergoing purifying selection. RNA-seq analysis revealed that SaCTL members, including duplicated genes, in the skin of parental discus show distinct expression patterns in different care stages and between male and female parents. The SaCTL11 was differentially expressed in most care stages and reached the maximum after eggs spawned, but the expression of its paired SaCTL14 was low in each stage. The SaCTL39 increased first and then decreased, reaching a peak in eggs spawned, while paired SaCTL48 first decreased and then increased, reaching a peak in hatched eggs. The SaCTL50 was differentially expressed only in female fish during care, but not in male fish. These results provide new insights into the evolution and potential functional differentiation of CTLs in discus fish during parental care. • A total of 186 CTLs were identified in discus fish genome.Sixty-five pairs of CTLs underwent tandem duplication. • Fifteen pairs of CTLs underwent segmental duplication. • Discuss CTLs exhibited a stage-specific and sex-dependent expression pattern during parental care. [ABSTRACT FROM AUTHOR]

Myoung, S.H.; Ji, H.-S.; Yu, H.-J.; Kim, H.J.; Kim, H.J., and Lee, B.-R., 2023. Ichthyoplankton assemblage structure in Jinhae Bay, Korea. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, 583-587. Charlotte (North Carolina), ISSN 0749-0208. Many studies on the species composition of ichthyoplankton have been conducted in Jinhae Bay. However, none have focused on the species' composition and distribution patterns. Therefore, herein, the species composition and distribution patterns of ichthyoplankton collected from January to December 2021 from Jinhae Bay, South Sea of Korea, were investigated. An oblique tow was collected from the bottom to the surface using a bongo net (80 cm, 330 µm) from eight stations. The collected samples were identified using morphological analysis and mtDNA cytochrome oxidase subunit I and 16S rRNA sequencing. A total of 66,938 ± 189,267 eggs/1000 m3 (mean ± Standard Deviation, SD) belonging to 30 species and 23 families, and 14,834 ± 31,325 larvae/1000 m3 from 45 species and 25 families, were collected from Jinhae Bay. The dominant egg species were Engraulis japonicus (93.4%), Repomucenus valenciennei (1.5%), and Nuchequula nuchalis (1.2%). Clupea pallasii (92.4%), R. valenciennei (2.5%), and E. japonicus (1.6%) were the dominant larval species. As a result of non-metric multidimensional scaling, fish were divided into two groups: One group spawns during low water temperatures and the other group spawns during high water temperatures. [ABSTRACT FROM AUTHOR]

Climate change in Arctic and sub-Arctic seas is leading to rapid changes in the dispersal potential of marine organisms. In Alaskan waters, loss of sea ice and salinity changes associated with warming may have a strong effect on the distribution and survival of eggs and larvae of key fish species at the Pacific–Arctic interface, such as polar cod (Boreogadus saida) in the Chukchi Sea and walleye pollock (Gadus chalcogrammus) in the northern Bering Sea. We conducted laboratory experiments to investigate how changes in ontogeny and salinity influenced the buoyancy and survival of eggs and larvae of these and two other gadids (Pacific cod, Gadus macrocephalus and saffron cod, Eleginus gracilis). Polar cod egg density varied among family groups, but eggs were more buoyant than those of walleye pollock overall. Eggs of both species followed a typical pattern of increasing density early in development. After hatching, polar cod and walleye pollock larvae were similar in density, and were notably more buoyant than the larvae of species with demersal eggs (Pacific cod and saffron cod). Larvae of the two Arctic species (polar cod and saffron cod) were less sensitive to salinity challenges than the sub-Arctic gadids, but polar cod became more sensitive at 6 weeks post-hatch. These results highlight possible adaptations of polar cod to ensure that their eggs are positioned under or near ice after spawning so that larvae hatch in productive surface waters during ice break-up. A comparison of modeled seawater densities to egg densities during the post-spawning period suggests that walleye pollock eggs would only be in contact with seasonal sea ice on the northern edge of their distribution at latitudes above ~ 63 °N. The synergic effects of environmental variables on vertical distribution of eggs and their survival potential will be important biogeographic mechanisms to consider with climatic warming and continued loss of sea ice. [ABSTRACT FROM AUTHOR]

The research focuses mainly on the ichthyoplankton of the Baltic deeps – the inflow route from the North Sea. The ichthyoplankton was represented by eggs and larvae of nine fish species: sprat, cod, herring, European flounder, fourbeard rockling, longspined bullhead, straightnose pipefish, sand goby and great sandeel. The species composition of ichthyoplankton varied depending on the location of a given site – the number of taxa ranged from one to five. The Slupsk Furrow was the most diversified area in terms of the number of taxa, while the highest abundance of ichthyoplankton occurred in the Bornholm Basin. The sprat clearly dominated and inhabited all the surveyed depths. Of the remaining species, only cod eggs as well as eggs and larvae of the fourbeard rockling significantly contributed to this formation. They occurred within their main spawning grounds (Bornholm Deep in the near-bottom layers) and secondary spawning grounds (Slupsk Furrow and Gdansk Deep) where salinity and oxygenation of water favored their development. Biometric research has shown that the diameter of eggs was within the size range typical of the Baltic Sea. [ABSTRACT FROM AUTHOR]

Dam presence results in heterogeneous aquatic environments that probably favour segregation of ichthyoplankton developmental stages. Therefore, the present study tested the hypothesis that dams in the Upper Uruguay River create heterogeneous aquatic environments favouring segregation of ichthyoplankton developmental stages and also separate species with different reproductive tactics. Ichthyoplankton were captured bimonthly during 2002–2015 in 25 sampling stations grouped by fluviometric characteristics. Sampling was performed at night, with cylindrical–conical plankton nets and light traps. After quantifying ichthyoplankton, we identified larvae to the lowest possible taxonomic level and classified them based on developmental stage and reproductive tactics. Egg abundance was higher in lotic environments, preflexion individuals were more abundant in transitional lotic/lentic environments, and the flexion stage was predominant in lentic environments. Larval assemblages consisted mainly of sedentary species or those with short reproductive migrations. Species with similar reproductive tactics occurred in different environments. In conclusion, we provided evidence demonstrating that mosaic environments in the Upper Uruguay River are important for life cycle completion of different fish species. These distinct habitat zones allow for successful spawning and offspring development, thus guaranteeing recruitment. [ABSTRACT FROM AUTHOR]

The eco-hydraulic diversity in a tidal reach is obviously enriched after spur dikes built, such as a turbulent rapid around structures head when tide ebbing and a gently dynamic environment in the back during the whole tide process. It would be much beneficial for adult fishes to spawn eggs and the youngs to fatten. Spur dikes have been utilized as channel regulation structures worldwide, especially in the upstream tidal reach of river estuary, where is a superexcellent habitat for resident fish or migratory fish during different life history stages. However, local hydraulic characters will be altered upon spur dikes establishment, resulting in several influence on fish habitat. The purpose of this paper was to reveal the impacts mechanism of spur dikes on fish habitat in a tidal reach through a comprehensive analysis based on some previous neglected aspects, such as fish physiological characters, hydraulic variations and essential factors alterations of the aquatic ecosystem. Hydraulic information around spur dikes was acquired through a 3D hydrodynamic model, and validations of tidal level, velocity and diversion ratio yielded a high accuracy. Turbulent rapid around spur dikes head and mild nearshore environment behind structures have some potentialities to become new spawning grounds, for fish spawning semi-pelagic eggs and fish laying adhesive eggs respectively. Benefitted from effective mixture of water during a tidal cycle, plenty of planktons and organic matters will be brought in and gradually enriched behind structures, thus a favorable feeding ground will appear there. Meanwhile, deflecting flow induced by spur dikes may cause some hazards for survival probability of migratory larval fish. It is drifted off the nearshore into the river middle, where is a higher turbulent intensity and less phytoplankton concentration. In summary, spur dikes possess tremendous ecological effects, i.e. enriching the eco-hydraulic diversity, not only as a velocity shelter. In addition, research result could afford a sufficient basis for environment conservations to restore aquatic ecosystem with spur dikes. [ABSTRACT FROM AUTHOR]

Substantial interannual variability in marine fish recruitment (i.e., the number of young fish entering a fishery each year) has been hypothesized to be related to whether the timing of fish spawning matches that of seasonal plankton blooms. Environmental processes that control the phenology of blooms, such as stratification, may differ from those that influence fish spawning, such as temperature‐linked reproductive maturation. These different controlling mechanisms could cause the timing of these events to diverge under climate change with negative consequences for fisheries. We use an earth system model to examine the impact of a high‐emissions, climate‐warming scenario (RCP8.5) on the future spawning time of two classes of temperate, epipelagic fishes: "geographic spawners" whose spawning grounds are defined by fixed geographic features (e.g., rivers, estuaries, reefs) and "environmental spawners" whose spawning grounds move responding to variations in environmental properties, such as temperature. By the century's end, our results indicate that projections of increased stratification cause spring and summer phytoplankton blooms to start 16 days earlier on average (±0.05 days SE) at latitudes >40°N. The temperature‐linked phenology of geographic spawners changes at a rate twice as fast as phytoplankton, causing these fishes to spawn before the bloom starts across >85% of this region. "Extreme events," defined here as seasonal mismatches >30 days that could lead to fish recruitment failure, increase 10‐fold for geographic spawners in many areas under the RCP8.5 scenario. Mismatches between environmental spawners and phytoplankton were smaller and less widespread, although sizable mismatches still emerged in some regions. This indicates that range shifts undertaken by environmental spawners may increase the resiliency of fishes to climate change impacts associated with phenological mismatches, potentially buffering against declines in larval fish survival, recruitment, and fisheries. Our model results are supported by empirical evidence from ecosystems with multidecadal observations of both fish and phytoplankton phenology. [ABSTRACT FROM AUTHOR]

• Sensitivity analysis on a larval drift model through an orthogonal experimental design enabling the quantification of main effects and their first-order interactions. • Larvae thermal tolerance is a key factor when modelling species at the limit of their distribution area. • At a large scale, nychtemeral vertical migration does not affect much the overall recruitment success. • Local hydrodynamics and inter-annual variability are the most important source of variations for recruitment success. • We advise simulating over multiple years before exploring recruitment success and connectivity outputs. Many marine fish species display a long larval drift between offshore spawning grounds and coastal nursery areas. This drift, whose efficiency drive the renewal of the population, critically depends on many environmental factors and on the spawning behaviour of species. Given the complexity to collect field data on fishes early life stages, modelling has proved to be one of the most valuable tool to explore such questions. However, these complex models require many parameters, many of which are uncertain, making a comprehensive sensitivity analysis a crucial step before drawing conclusions on the effects of environmental drivers. This study focused on the larval drift of five species archetypes mimicking five commercially important fish species with contrasted spawning strategies and larval ecology, in five different sub regions over Western Europe, from the Iberian coast to the North Sea. Using an hydrodynamic model (MARS3D) coupled with an individual-based model, and by building a simulation design suitable for such sensitivity analysis, we assessed the relative influence of extrinsic (years and region's hydrodynamics) and intrinsic (spawning grounds' depth, spawning period, vertical migration, developmental rate, daily mortality and tolerance to temperature) factors and their two-ways interactions on recruitment success to nurseries. The thermal tolerance of species was one of the leading factors, suggesting that this is a critical parameter, especially when modelling species recruitment success at the edge of their distribution range. On the other hand, other parameters such as the nycthemeral vertical migration, that are often discussed in such larval drift simulation exercise, have proved to have a more limited influence for an analysis at such a large spatial scale. Overall, when studying larval drift on a large scale, local hydrodynamics and inter-annual variations hold most of the explained variance in the recruitment success, confirming the importance of repeating simulations over multiple years before exploring the connectivity among spawning and nursery areas. [ABSTRACT FROM AUTHOR]

The Neotropical fish fauna comprises approximately 6080 species, of which almost 3000 inhabit the Amazon River basin. However, the construction of hydroelectric dams has threatened this biodiversity by habitat fragmentation. To uncover the putative effect of river impoundment on migratory fish species, over 5400 eggs and larvae were collected from the Teles Pires River, including five tributaries and the hydroelectric reservoir, which were identified using the COI metabarcoding approach. Identification of early life stages allowed the detection of >40 fish species, including at least 27 migratory species. Fish eggs were assigned to nine families, 13 genera, and 23 species, whereas larvae were attributed to 12 families, 18 genera, and 34 species. Eggs and larvae of migratory fishes were primarily present in tributaries upstream of the dam, with fewer in the reservoir. A putative impact of the dam on the ichthyoplankton community was detected, with a significant difference found between the reservoir and tributaries for larval species richness (r = 0.822, p = 0.0211). In contrast, no significant difference was recovered among tributaries for both eggs (r = 0.213, p = 0.2657) and larvae (r = 0.378, p = 0.0696). However, a change in ichthyoplankton assemblage was observed between tributaries, as revealed by beta diversity analyses. These results highlight the potential of ichthyoplankton metabarcoding for studying and biomonitoring of migratory fishes, as well as providing relevant data concerning the identification of spawning sites to set guidelines for fisheries management and effective conservation of fish populations. [Display omitted] • Hydroelectric power plant dams block migratory routes for fish spawning. • Metabarcoding is a powerful method to identify ichthyoplankton and spawning areas. • Amazonian tributaries are used as spawning areas for several migratory fish species. • Fewer migratory fish spawn at sites near the river impoundments. • Ichthyoplankton identification should consider metabarcoding as a prime approach. [ABSTRACT FROM AUTHOR]

Highlights • The connectivity network presented variations in the relative role of each MPA. • Southern MPAs showed the highest number of connections and high self-recruitment. • Source-sink index suggested that southern MPAs were source of larvae. • Central MBRS locations might be a source of larvae. • Four zones were differentiated and associated with circulation patterns. Abstract The potential connectivity network of marine protected areas (MPAs) with spawning aggregations sites in the Mesoamerican Barrier Reef system (MBRS) was examined through simulated dispersal of two study cases, Lutjanus analis and Epinephelus striatus larvae. The analysis was based on a particle tracking model incorporating four years of daily horizontal surface currents from the global scale HYCOM 1/12°. We carried out two approaches, the first one used the period of larval duration (PLD) and the second the time of flexion of the notochord as the limit time of dispersion of the particles. Additionally, peak spawning seasons (December-Febraury for E. striatus and March-July for L. analis), lunar phases and georeferenced spawning aggregations sites were considered for releasing the virtual larvae. Our findings suggest that in general, the network of MPAs of the MBRS are well connected, however, the connectivity network structure presented variations in the relative role of each MPA, and their played role will depend on the specie reproductive period, the oceanographic conditions and the assumed biological approximation (such as PLD or flexion). Our analysis suggested a regionalization of the MBRS. A southern region (Bacalar Chico, Roatan and Sapodilla) with low degree of connectivity, moderate self-recruitment rate, and low values of betweenness centrality. A second southern region (Turneff Island, Lighthouse Atoll, Glover Reef Atoll and Gladen Spit) with high rate of self-recruitment (up to 20%) that could be related to self-recruitment due to retention mechanism of the Honduras Gyre, with high values of source of larvae, function as bridges that connect the south zone with the north of the system. A third region (Mahahual and Xcalak) showing sink of larvae, low larval arrival rate but self-recruitment, low values of betweenness centrality area influenced by slow and variable currents and the presence of a southward flow. And a fourth region (Chinchorro, Sian Ka'an, Puerto Morelos and Cozumel) with moderate fast current speed (Yucatan Current), low self-recruitment, larval sink, bridge with the Gulf of Mexico and Florida. [ABSTRACT FROM AUTHOR]

Little is known about the mechanism of transport that enables age-0 sablefish (Anoplopoma fimbria) to reach suitable nursery sites from spawning locations far offshore, or the strength of the connection between individual spawning sites and nursery areas, or how variability in the strength of these connections may impact recruitment success. Using a model for the early life stages of sablefish, we explored the variability in connectivity between spawning and recruitment sites that can arise solely from interannual variability in environmental forcing and its impact on transport. Our major findings are that 1) the model indicates young sablefish settling in nursery areas in the Gulf of Alaska were most likely spawned in the eastern Gulf; 2) sablefish spawned in the western Gulf of Alaska are unlikely to settle anywhere in the Gulf, and are more likely to be advected farther west, perhaps to settle in the Aleutian islands or Bering Sea (to contribute to the Alaska population, they would have to undergo an active return migration as they mature); 3) total connectivity between all spawning sites and nursery areas showed stronger correlation with recruitment estimates than the strength of connections to or from specific regions; and 4) transport to St. John Baptist Bay, a known sablefish nursery area, was not the most probable end point for sablefish spawned throughout our Gulf of Alaska model domain. This suggests that young individuals arrive at this persistent nursery area due to directional swimming behavior, highly localized spawning, or small-scale currents not captured in the hydrographic model. The fact that no single correlate in our analysis had a very strong relationship to sablefish recruitment indicates that recruitment variability arises from complex interactions between the environment and the individual, and a possible disconnect in spatial scales between the Gulf of Alaska sablefish IBM and the broader sablefish stock assessment, which includes both the GOA and the Eastern Bering Sea, as well as possible contributions from Canadian stocks to the south. Our analyses determined that although the timing and extent of this transport shows significant interannual variability, both the location of likely sablefish spawning (source) areas and the comparative strength of connectivity between spawning and nursery sites appear to be relatively consistent year-to-year. [ABSTRACT FROM AUTHOR]

Methods for milt collection and chilled preservation, hormone-induced spawning and artificial fertilization were studied in Nile tilapia Oreochromis niloticus. Milt samples were selected from 5 male brooders. Each milt sample was divided into 4 treatments; 3 treatments were centrifuge-washed with 0.85% normal saline solution (NSS), and then added with the extenders (1) freshwater fish saline (FFS) or (2) modified fish Ringers solution (MFS), or without an extender as (3) NSS (control), while the fourth treatment was the unwashed control. Milt samples treated with either extender at 4 °C presented a sufficient sperm motility score (≥ 3) and sperm viability (≥ 70%) for up to 20 h post-collection. For female brooders, gonadotropin-releasing hormone analog (GnRHa) was used to induce spawning. The highest number of females spawned and a pseudo-gonadosomatic index were observed in groups that received two GnRHa injections (15 and 30 μg kg−1, 8 h interval) with an oral administration of a dopamine antagonist (5 mg kg−1). Artificial fertilization was performed with fresh and 20 h chilled-storage milt. Mean fertilization rates for the fresh and chilled milt fertilized groups were 83.6 ± 7.2% and 42.3 ± 5.1%, respectively, with hatching rates of 67.5 ± 3.5% and 28.3 ± 6.8%, respectively. Nevertheless, the development of fish larvae from both groups was comparable. This study indicated that artificial fertilization using chilled milt and GnRHa-induced-spawn produced healthy tilapia fry. Thus, the procedures facilitate breeding programs of Nile tilapia in pair mating selection and distribution of genetic materials. • A practical technique was developed to provide competent quality of tilapia sperm preserved at 4 °C for up to 20 h. • Spawning synchronization was accomplished with 2 GnRHa injection with an oral administration of the dopamine antagonist. • The embryo obtained from artificial fertilization using chilled milt and induced spawn eggs showed typical development. • The reproductive technique demonstrated in this study did not cause injury to the broodfish. [ABSTRACT FROM AUTHOR]

The basic biology and ecology of the South African east coast round herring Etrumeus wongratanai was investigated from samples of fish collected between 2013 and 2016. This species is short‐lived and reaches a maximum of 3 years of age, with rapid growth in its first year of life. It reproduces from June to December (austral summer) and condition factor was lowest in May through to August and increased from September, probably reflecting the physiological strain before and during spawning. Fish larvae were the most important food items consumed during summer, whereas eucalanid copepods were the most important prey at other times of the year. Stable‐isotope data suggest that there are gradual changes in the trophic level with increasing fish size, δ15N and δ13C values also differed between seasons. The results obtained here are compared with those of other Etrumeus species, regionally and globally. [ABSTRACT FROM AUTHOR]

Understanding the relationship between intraspecific phenotypic variation and habitat is fundamentally important to ecology and evolution. However, it is largely unknown whether the environment drives the morphological variation in riverine fish otoliths, which are potential phenotypic markers. In this study, we investigated morphological variations in the otoliths of an endemic Chinese fish (Schizothorax nukiangensis Tsao) collected from seven sites with varying environmental gradients along the Nu‐Salween River. We compared morphological characters of S. nukiangensis otoliths among sampling sites and identified environmental sources of otolith morphological variation using multivariate regression trees and multiple factor analysis. Results showed that S. nukiangensis otoliths collected from different habitats were significantly different in morphology, mainly at the rostrum, excisura and posterior rim. Variations in otolith morphology (specifically the increase in otolith length) were predominantly governed by average river gradient; this might be a functional response to hydrogeomorphic conditions. Other environmental gradients (i.e., altitude, latitude and average annual temperature) played a minor role in otolith shape. This study highlighted the role of environmental factors in determining the otolith shape in riverine fish; thus, species and population discriminations based on otolith morphology should consider intraspecific variability. [ABSTRACT FROM AUTHOR]

The spawning success of lithophilic salmonids is strongly influenced by the fine sediment content ("fines") of spawning substrates, yet knowledge on the impacts of fines on the spawning of non‐salmonid lithophiles remains limited, despite their ecological and socio‐economic importance in European rivers. Consequently, the aim here was to use an ex‐situ experiment to investigate the impact of sand content on egg survival and timing of larval emergence of the surface‐spawning cyprinid European barbel Barbus barbus. Thirty incubator boxes within a recirculating system were filled with one of five experimental sediment mixtures (0%–40% sand by mass) that each contained 300 fertilised eggs at a depth of 50 mm. Emerged, free‐swimming larvae were captured and counted daily to assess grain‐size effects on larval survival and emergence. Specifically, total proportion of emerged larvae, cumulative daily proportion of emerged larvae and time required to reach 50% emergence were measured during the study. Whilst the proportion of sand in the sediments did not have a significant impact on egg‐to‐emergence survival (mean survival per treatment 75%–79%), it significantly affected the timing of larval emergence to the water column; early emergence was detected in treatments with elevated sand content (on average, 50% emergence after 12–13 days versus 19 days in the control). Similar to findings from salmonid studies, these results suggest high sand content in spawning gravels can influence timing of larval emergence and potentially cyprinid lithophilic fish survival. [ABSTRACT FROM AUTHOR]

Turbidity can fluctuate rapidly during the early life of fishes, impacting foraging behaviours. For piscivores, turbidity may hinder foraging, whereas planktivores and juvenile fishes may increase foraging activity and decrease antipredator behaviours in moderate levels of turbidity. Black crappie (Pomoxis nigromaculatus) and white crappie (P. annularis) population trends are often related to changes in turbidity. Yet effects of turbidity on juvenile foraging of these species are unknown and may differ between species. To evaluate effects of three turbidity levels (0, 25 and 50 NTU) on juvenile crappie foraging, controlled experiments compared (a) consumption and size selection for a single prey and (b) selection, total consumption and energetic value of diets when offered three distinct prey options. Overall, black crappies exhibited universally greater diet biomass than white crappies. Black crappies displayed higher prey consumption and were more size selective of a single‐prey type, whereas white crappies were less size selective and maintained uniform consumption as turbidity increased. Selection patterns for three prey types were similar among species and turbidity levels, with Chaoborus preferred and Chironomus avoided. However, black crappies also avoided Daphnia, whereas white crappies consumed them neutrally. Overall, turbidity did not impair foraging of juvenile crappies. Turbidity‐driven fluctuations in prey base paired with predator interactions likely also contribute to observed growth and abundance fluctuations in natural systems. [ABSTRACT FROM AUTHOR]

Sea urchin fishery has gradually expanded in different countries and territories around the world, including South America, and the sea urchin Tripneustes depressus is a feasible candidate for aquaculture. The aim of this study was to prepare a biotechnical protocol for rearing larvae and production of juveniles. Large T. depressus were collected at monthly intervals at a subtidal rocky coast off Palmar, Santa Elena, Ecuador from January 2015 to December 2017. T. depressus spawns when exposed to thermal shock in low illumination room. Seven spawning events were recorded between March and May and between July and August. On average, females spawned approximately 3.60 ± 0.83 × 10 7 oocytes (mean diameter: 78.4 ± 2.1 μm) and males spawned approximately 5.60 ± 1.10 × 10 7 spermatozoa respectively). A cohort of May 13, 2017 was followed for 250 days. Embryo and larval stages were completed within 48 h and 21 days, respectively, at 26.5 ± 0.5 °C. Larvae were fed a mixed diet of Tysochrisis lutea , Chaetoceros gracilis and Rhodomonas sp. at concentrations ranging from 2.5 × 10 3 to 2.0 × 10 4 cells /ml as they increased in size. Larvae were measured considering: Total Length (TL), Medium Base Line (MBL) and Base Width (BW). On day 2 after fertilization (AF): 311.7 ± 2.0 μm, 158.9 ± 1.0 and 270.7 ± 3.4 ( n  = 10), respectively. On AF 16 : 544.7 ± 4.0 μm, 273.6 ± 6.9 and 355 ± 3.5 (n = 10). On AF 21 , larval rudiment size was equal in size to that of the stomach and larvae were competent. Their body measurements, and specifically total length at that food concentration, showed no phenotypic plasticity. Thirty two days post spawning (DPS) all juveniles had open mouths and a functional gut for feeding (size: 0.40 ± 0.01 mm DT), and at DPS 98 three size categories were differentiated. Sea urchin sizes by categories at DPS 98 and DPS 152 were, respectively: small (2.20 ± 0.1 mm DT and 23.9 ± 0.45 mm TD), medium (4.90 ± 0.08 mm DT and 33.3 ± 0.3 mm TD); and large (7.20 ± 0.11 mm DT and 43.8 ± 0.5 mm DT) with zero mortality. T. depressus reach 4 cm diameter at 188 days after metamorphosis and can reproduce after six months of life, when it reach approximately 4.2 cm diameter), although the gonads are not yet commercial in size. This protocol is an initial perfectible protocol for sea urchin aquaculturing. However, we have made recommendations for consideration that include increasing survivorship and supplying post-larvae for juvenile production. [ABSTRACT FROM AUTHOR]

An understanding of the reproductive biology of a species is fundamental to successful management of fish stocks. Rockfish ( Sebastes spp.) have complex reproduction, being viviparous and generally late to mature, often with extended adolescent periods characterized by abortive maturation events. Furthermore, whereas the majority of Sebastes species in the California Current region produce one brood of larvae annually, several are known to produce more than one, though no stock assessments have yet considered the impact multiple brooding may have on population spawning potential for these species. We documented abortive maturation and examined the prevalence and size-dependent and regional patterns of multiple brooding using macroscopic evaluation and detailed histological analysis of ovaries from a model species, chilipepper ( S. goodei ), collected off Central and Southern California. We modeled the size-related maternal effect on the probability of multiple brooding, and quantified size-dependent fecundity relationships. Our results indicate that the most robust estimation of reproductive output, as a function of the fecundity-length relationship, is improved for chilipepper when multiple brooding is incorporated, due to the greater probability of additional broods, and thus greater spawning potential, in larger females. [ABSTRACT FROM AUTHOR]

We studied the abundance, size and growth rates of Engraulis anchoita larvae during the end of the species’ spawning season in relation to environmental variables. Two sampling transects, one in Península Valdés (northern transect: NT) and the other in Isla Escondida (southern transect: ST), with four stations each, were established in late summer. Both locations are characterized by high concentrations of E. anchoita larvae in spring, strongly associated with the presence of frontal waters, at the beginning of the species’ spawning season. Zooplankton and ichthyoplankton were sampled, and temperature profiles and chlorophyll- a satellite images were analyzed for each sampling station. Zooplankton samples were divided in size fractions, and composition and abundances were estimated. Standard length (SL), ontogenetic stages, and abundance (including eggs) were estimated. Additionally, age and growth rates were determined by otolith analysis. Two different scenarios were observed in both transects. In the NT, a frontal structure was found, while at the ST, the water column was completely homogeneous. Total zooplankton abundance was maximum at frontal waters, with 22,195 ind. m −3 , being the small size fraction (<200 μm) the most abundant, mainly composed of nauplii (9000 ind. m −3 ) and cyclopoid copepodites (4000 ind. m −3 ). The NT showed higher abundance (mean of 126.5 ind. m −2 per station in NT; 29.75 ind. m −2 in ST), faster growth rates of E. anchoita larvae (NT: 0.45 ± 0.04 mm day −1 ; ST: 0.34 ± 0.09 mm day −1 ; n = 90), and higher mean SL at frontal waters (7.57 ± 1.52 mm SL) than the ST. In the NT, E. anchoita growth rates were constant in time, whereas in the ST, they decreased with age. Our results support the classical theory, which states that frontal waters provide advantageous environmental conditions for fish larvae feeding, growth and, thus, survival. [ABSTRACT FROM AUTHOR]

Abstract: Swordfish Xiphias gladius (Linnaeus, 1758) are a circumglobal pelagic fish targeted by multiple lucrative fisheries. Determining the distribution of swordfish larvae is important for indicating reproductive activity and understanding the early life history of swordfish. We identify and characterize larval swordfish distributions during peak swordfish spawning throughout the Gulf of Mexico and western Caribbean Sea with generalized additive models (GAMs) using catches of swordfish larvae during ichthyoplankton surveys in April and May of 2010, 2011, and 2012. The best fit GAM, as determined by stepwise, backward Akaike Information Criterion selection, included both physiochemical (temperature at 5 m, sea surface height anomaly (SSHA), eddy kinetic energy (EKE)), temporal (lunar illumination, hour of sampling) and spatial (location) variables, while near surface chlorophyll a concentration residuals remained as a random effect. The highest probability of larval swordfish catch occurred at sub‐surface temperatures, SSHA, and EKE values indicative of boundary currents. Standard lengths of larvae were larger further downstream in the boundary currents, despite high variability in length with location due to multiple spawning locations of swordfish near these currents. Probability of larval swordfish catch also peaked during the crescent and gibbous moons, indicating a lunar periodicity to swordfish spawning. These results suggest that swordfish may spawn during select moon phases near boundary currents that transport their larvae to larval and juvenile habitat including the northern Gulf of Mexico and coastal waters of the southeast United States. [ABSTRACT FROM AUTHOR]

Tunas show a wide variety of life history strategies, spatial distributions and migratory behaviors, yet they share a common trait of spawning only in tropical and sub-tropical regions. The warm-water tuna species generally show significant overlap between spawning and feeding grounds, and longer spawning seasons of several months to near year-round. In contrast, the cool-water bluefin tunas migrate long distances between feeding and spawning grounds, and may spawn over periods as short as 2 months. Here, we examine the spatial distributions of tuna larvae in the world's oceans, and examine interspecific differences in the light of adult behaviors and larval ecology. We discuss the links between larval tuna and their oceanographic environments and relate these to current knowledge of larval growth, feeding and trophodynamics, with a focus on the better-studied bluefin tunas. We show that larval tunas have moderate to fast growth rates and selective feeding habits, and thus appear to be adapted for survival in warm, oligotrophic seas. We also examine the challenges of sustainably managing species which migrate across multiple management boundaries to reach spatio-temporally restricted spawning grounds and discuss the previous and future anthropogenic impacts on tuna spawning areas. [ABSTRACT FROM AUTHOR]

Larval growth from three putative populations was estimated by microstructure analysis of otoliths of four year classes of adult herring sampled over a wide spawning season (February-June) in and around an inland brackish water lake (Landvikvannet) in southern Norway during the years 2012–2015. Mean width of daily increments at distances between 20 and 170 μm from the otolith core were significantly higher in Landvik herring (peak spawning in May) compared with the two other populations, Coastal Skagerrak spring spawners (peak spawning in March-April) and Norwegian spring spawning herring (peak spawning in February-March). These population differences were observed for all studied year classes and years and highly consistent with expected temperature dependent larval growth based on timing of successive spawning events. The observed patterns imply that timing of spawning was population specific with a tendency of adult herring to spawn at the same time and under the same conditions as they hatched themselves. This was also supported by vertebral counts, which are negatively correlated with temperatures during the embryonic stage. Firstly, Landvik herring which experienced higher ambient temperature during the embryonic stage were characterised by significantly lower counts than herring from the two other populations. Secondly, daily otolith growth also tended to decrease with increasing vertebral counts within the populations. The present study signifies the importance of otolith growth history for population discrimination in herring, even within the same spawning season, and further supports the use of vertebral counts in the continuous discussion on herring population structure, assessment and management. [ABSTRACT FROM AUTHOR]

Patterns in larval transport of coastal species have important implications for species connectivity, conservation, and fisheries, especially in the vicinity of a strengthening boundary current. An Ocean General Circulation Model for the Earth Simulator particle tracking model was used to assess the potential dispersal of Eastern King Prawn ( EKP) larvae Melicertus (Penaeus) plebejus, an important commercial and recreational species in Eastern Australia. Particles were exposed to a constant natural mortality rate, and temperature-dependent growth (degree-days) was used to determine the time of settlement. Forward and backward simulations were used to identify the extent of larval dispersal from key source locations, and to determine the putative spawning regions for four settlement sites. The mean dispersal distance for larvae was extensive (~750-1,000 km before settlement), yet the northern spawning locations were unlikely to contribute larvae to the most southern extent of the EKP range. There was generally great offshore dispersal of larvae, with only 2%-5% of larvae on the continental shelf at the time of settlement. Our particle tracking results were combined with existing site-specific reproductive potentials to identify the relative contributions of larvae from key source locations. Although mid-latitude sites had only moderate reproductive potential, they delivered the most particles to the southern coast and are probably the most important sources of larval EKP for the two southern estuaries. Our modelling suggests that mesoscale oceanography is a strong determinant of recruitment success of the EKP, and highlights the importance of both larval dispersal and reproductive potential for understanding connectivity across a species' range. [ABSTRACT FROM AUTHOR]

In this study the drift of eastern Baltic cod larvae and juveniles spawned within the historical eastern Baltic cod spawning grounds was investigated by detailed drift model simulations for the years 1971–2010, to examine the spatio-temporal dynamics of environmental suitability in the nursery areas of juvenile cod settlement. The results of the long-term model scenario runs, where juvenile cod were treated as simulated passively drifting particles, enabled us to find strong indications for long-term variations of settlement and potentially the reproduction success of the historically important eastern Baltic cod nursery grounds. Only low proportions of juveniles hatched in the Arkona Basin and in the Gotland Basin were able to settle in their respective spawning ground. Ocean currents were either unfavorable for the juveniles to reach suitable habitats or transported the juveniles to nursery grounds of neighboring subdivisions. Juveniles which hatched in the Bornholm Basin were most widely dispersed and showed the highest settlement probability, while the second highest settlement probability and horizontal dispersal was observed for juveniles originating from the Gdansk Deep. In a long-term perspective, wind-driven transport of larvae/juveniles positively affected the settlement success predominately in the Bornholm Basin and in the Bay of Gdansk. The Bornholm Basin has the potential to contribute on average 54% and the Bay of Gdansk 11% to the production of juveniles in the Baltic Sea. Furthermore, transport of juveniles surviving to the age of settlement with origin in the Bornholm Basin contributed on average 13 and 11% to the total settlement in the Arkona Basin and in the Gdansk Deep, respectively. The time-series of the simulated occupied juvenile cod habitat in the Bornholm Basin and in the Gdansk Deep showed a similar declining trend as the Fulton’s K condition factor of demersal 1-group cod, which may confirm the importance of oxygen-dependent habitat availability and its effect on density dependence as a process relevant for recruitment success. [ABSTRACT FROM AUTHOR]

This study revealed the spatial variation in abundance and body size of larval fishes in the Seto Inland Sea, Japan, in January 2014 and 2015. Fish larvae were collected by a 1.3-m-diameter ring net towed at the surface and at 10-m depth at 21 stations. The most dominant species was the sandlance Ammodytes japonicus, constituting 82% of total larval fish caught. The body size of A. japonicus was greater [ca. 9 mm total length (TL) in 2014] in eastern areas than in western areas (ca. 5 mm TL in 2014). This trend was also observed in rockfishes ( Sebastiscus marmoratus and Sebastes inermis species complex), suggesting a common phenomenon in this region. Because the water temperature was lower in eastern areas, it is likely that the longitudinal differences in larval body size are attributable to earlier spawning in eastern areas caused by different temperature conditions. [ABSTRACT FROM AUTHOR]

Phenology of fish spawning in lotic ecosystems depends on interactions between species life history strategies and patterns of environmental variation related to hydrology and seasonality. To further study these relationships, we examined patterns of larval fish abundance in relation to discharge and other environmental variables in the Brazos and Trinity rivers, Texas. From March 2013 to March 2014, environmental data and larval fishes were collected twice each month using drift nets. Multivariate analyses indicated that, at both study sites, water temperature was the primary mechanism driving temporal and taxonomic variation in larval fish assemblage structure at the family level. However, in the Trinity River, assemblage structure was significantly associated with discharge, albeit to a lesser degree than with water temperature. Cyprinid protolarvae dominated catches in both rivers and did not seem to be constrained by any aspect of the flow regime, as evidenced by their high abundance throughout the reproductive season (April–September). Analysis of larval fish abundance at the family level compromised our ability to infer spawning dynamics of species classified as fluvial specialists. Further research enabling identification of larvae to species-level is needed to elucidate how flow regime components influence reproduction and recruitment of fluvial specialists. [ABSTRACT FROM PUBLISHER]

Effective and sustainable management depends on knowledge of spawning locations and their relative contributions to marine fish populations. Pacific cod ( Gadus macrocephalus ) in the southeastern Bering Sea aggregate at discrete spawning locations but there is little information on patterns of larval dispersal and the relative contribution of specific spawning areas to nursery habitats. Age-0 Pacific cod from two cohorts (2006 and 2008) were examined to address the following questions: (1) does size, age, and otolith chemistry vary among known capture locations; (2) can variation in elemental composition of the otolith cores (early larval signatures) be used to infer the number of chemically distinct sources contributing to juvenile recruits in the Bering Sea; and (3) to what extent are juvenile collection locations represented by groups of fish with similar chemical histories throughout their early life history? Hierarchical cluster (HCA) and discriminant function analyses (DFA) were used to examine variation in otolith chemistry at discrete periods throughout the early life history. HCA identified five chemically distinct groups of larvae in the 2006 cohort and three groups in 2008; however, three sources accounted for 80–100% of the juveniles in each year. DFA of early larval signatures indicated that there were non-random spatial distributions of early larvae in both years, which may reflect interannual variation in regional oceanography. There was also a detectable and substantial level of coherence in chemical signatures within groups of fish throughout the early life history. The variation in elemental signatures throughout the early life history (hatch to capture) indicates that otolith chemical analysis could be an effective tool to further clarify larval sources and dispersal, identify juvenile nursery habitats, and estimate the contributions of juvenile nursery habitats to the adult population within the southeastern Bering Sea. [ABSTRACT FROM AUTHOR]

The addition of juveniles to marine populations (termed “recruitment”) is highly variable due to variability in the survival of fish through larval and juvenile stages. Recruitment estimates are often large or small for several years in a row (termed “autocorrelated” recruitment). Autocorrelated recruitment can be due to numerous factors, but typically is attributed to multi-year environmental drivers affecting early life survival rates. Estimating the magnitude of recruitment autocorrelation within a stock assessment model and examinations on its effect on the quality of forecasts of spawning biomass within stock assessments is uncommon. We used a simulation experiment to evaluate the estimability of autocorrelation within a stock assessment model over a range of levels of autocorrelation in recruitment deviations. The precision and accuracy of estimated autocorrelation, and the ability of an integrated age-structured stock assessment framework to forecast the dynamics of the system, were compared for scenarios where the autocorrelation parameter within the assessment was fixed at zero, fixed at its true value, internally estimated within the integrated model, or input as a fixed value determined using an external estimation procedure that computed the sample autocorrelation of estimated recruitment deviations. Internal estimates of autocorrelation were biased toward extreme values (i.e., towards 1.0 when true autocorrelation was positive and −1.0 when true autocorrelation was negative). Estimates of autocorrelation obtained from the external estimation procedure were nearly unbiased. Forecast performance was poor (i.e., true biomass outside the predictive interval for the forecasted biomass) when autocorrelation was ignored, but was non-zero in the simulation. Applying the external estimation procedure generally improved forecast performance by decreasing forecast error and improving forecast interval coverage. However, estimates of autocorrelation were shown to degrade when fewer than 40 years of recruitment estimates were available. [ABSTRACT FROM AUTHOR]

Understanding lunar periodicity in spawning is necessary for guiding studies on reproduction in fishes, but is unknown for the abundant and economically important white grunt, Haemulon plumierii (Lacepede, 1801). We sampled mature white grunts in the eastern Gulf of Mexico during each of the four lunar periods of April 2016, coinciding with the seasonal peak of their spawning activity. Spawning-capable white grunts were macroscopically distinguishable from actively spawning fish, which we further confirmed microscopically. There was a clear lunar pattern with peak oocyte hydration and presence of flowing milt (i.e., actively spawning fish) during the full moon. A full moon spawn may be advantageous to juveniles settling during the following new moon after a short pelagic larval duration previously determined to be approximately 14 d. These findings can guide future research seeking to quantify either batch fecundity or production of white grunts by identifying the lunar period during which sampling should occur. [ABSTRACT FROM AUTHOR]

The East China Sea (ECS) is one of the most important fish spawning and nursery grounds in the north Pacific. Even though summer is an important spawning season for many fishes in the region, large-scale molecular identification studies on ichthyoplankton during this season are few. In this study, we sampled 8,933 fish eggs and 12,161 fish larvae from 25 stations during the summer of 2009. Using DNA barcoding, a number of the fish eggs and larvae were identified and classified into 45 and 124 taxa, respectively. Principal component analysis (PCA) categorized the inshore stations of the Changjiang Diluted Water area as having the hydrographic features of low sea surface temperature (SST), salinity (SSS) and high chlorophyll a (SSC) contents, whereas the continental shelf and offshore stations under the influence of the Kuroshio Current displayed the opposite results. Ichthyoplankton was more abundant at the inshore stations than the offshore stations, but species diversity was lower at the former locations. Species compositions of both fish eggs and fish larvae at the 25 stations were categorized into three different assemblages based on a non-metric multidimensional scaling analysis. Combining the assemblage patterns of ichthyoplankton with the results of the PCA and satellite images of SST and SSC showed that the assemblage patterns of fish eggs were correlated with water mass, while those of the fish larvae were not. [ABSTRACT FROM AUTHOR]

This study was undertaken to determine the spawning season of the nurseryfish, a species with a unique method of parental care found only in northern Australia and southern New Guinea. Monthly samplings with an ichthyoplankton net at the same locality in the Adelaide River over multiple years yielded no larval nurseryfish in February, March, April and May. Larvae first appeared in June and were collected each month until January. From this we conclude that the nurseryfish spawning season in the Adelaide River is June-January. Twelve other larval fish species from 10 families were collected in the plankton tows with nurseryfish. Larval nurseryfish are readily identified and separated from other larval fishes by their peculiar rib anatomy, an important diagnostic character of Kurtus. The development of the unusual rib anatomy is examined with three-dimensional micro-computerised tomography scans of 12-21-mm standard length (SL) specimens. The bony protection of the swim bladder formed by the ribs is visible in the smallest postflexion specimens examined and is essentially complete by 19mm SL. These ecological and anatomical observations add another pixel to the big picture of nurseryfish life history. [ABSTRACT FROM AUTHOR]