Search

Reproduction is one of the most important biological aspects for the maintenance of viable populations, and understanding the spatial and seasonal patterns in the reproduction of Neotropical fish is a point that still needs considerable investigation. In this study, the main aim was to reduce knowledge gaps concerning fish eggs and larvae distribution patterns. Therefore, the River Araguaia basin, one of the main hydrographic basins of the Neotropical savanna, was used as the focal point of study. Samplings of fish eggs and larvae were carried across the hydrological regime during flooding and drought events between December 2018 and July 2020 at 15 sites distributed along a 350 km stretch of the River Araguaia basin. Fish eggs and larvae were found in all sampling sites, with the highest number of catches in the flood season. The fish larvae were represented by 5 orders, 22 families and 22 at the genus or species level. Both environments, tributary and main channel of the River Araguaia, are important for fish reproduction, and no difference was found in the use between the main channel and the tributaries. The results showed that spatial factors are important to explain the change in larval composition, which may have a wide or restricted distribution related to specific habitats. The main factors related to the reproductive activity of fish in this region are the physical and chemical changes in the water that occur in the flood season. These results indicate that the River Araguaia basin has environmental integrity and provides favourable conditions for the reproductive activity of fish, including long‐distance migratory species. Considering this, mitigate measures that guarantee the preservation of the natural flow are crucial for the maintenance of fish biodiversity. [ABSTRACT FROM AUTHOR]

Acceptance sampling is important for food safety and is a relevant tool at production and official control levels, as it helps decision-making processes and verifies quality and food safety management. Generally, sampling plans are hypothesis tests of products that have been submitted for official appraisal and subsequent acceptance or rejection. The sample size is related to the set level of risk, the acceptable precision, and the tolerable misstatement size; therefore, sample size determination has a crucial role in setting up the accepted level of non-compliance and level of error. Using a simple predictive model based on combinatorics, this study showcases how sample size management can change the probability of rejecting good lots and/or accepting bad lots when the acceptance number is 0 (c=0). We showed that when c=0, a very high level of significance of the test corresponds to the high probability of rejecting a lot with an acceptable prevalence of defective items (type II error). We produced tables about the minimum sample size at different significance levels, which can be useful in the field. A paradigmatic example of the role of sample size in the acceptance-sampling plan is represented by the visual inspection for the detection of Anisakid larvae in fishery products. This study investigated this aspect and mainly referred to studies on the prevalence of larvae in farmed fish. We showed that, for lots =1000 items, the sample size is not strictly related to the lot size, but to draw a consistent control plan and reduce the variability in the clinical judgment, control authorities require a standardized approach. Because of this, the results on the prevalence of Anisakid larvae in farmed fish, if only based on sampling control plans, do not support a negligible risk statement, despite the claims reported in the EFSA opinion and several other studies. [ABSTRACT FROM AUTHOR]

Mesocyclops leuckarti is a zooplankton that is potentially suitable as a live food for freshwater fish larvae. Aquaculture farmers often struggled to create nutritious live feed to maximize the production of larval fish. This study aimed to determine the effects of different enrichments on life-table parameters, protein, lipid and fatty acid content of M. leuckarti when enriched with different dietary enrichments. In this study, five treatments for raising the copepod were compared: rice bran, soybean meal, Chlorella sp., Spirulina sp., and unenriched (control). The results showed that M. leuckarti after 16 days of cultivation enriched with rice bran produced a higher population density (53.3 ind/ml) and survival rate (97.4%) than when cultivated with any of the other diets. In terms of nutritional value, protein content was higher in M. leuckarti enriched with rice bran (52% DW) and soybean meal (53% DW). However, lipid content was highest in M. leuckarti enriched with rice bran (14% DW). Fatty acids, such as α -linolenic acid ALA (7.21%) and docosahexaenoic acid DHA (6.26%) were higher in M. leuckarti enriched with rice bran. Eicosapentaenoic acid EPA (7.16%) and arachidonic acid ARA (7.74%) were higher in M. leuckarti enriched with Chlorella sp. This study suggests that organic by-products are better sources for strengthening and improving the growth performance and life history of this copepod, and possibly also of zooplankton organisms in general. [ABSTRACT FROM AUTHOR]

1. Intermittent streams are hydrologically dynamic within and among years, leading to episodic bouts of local extirpations and subsequent recolonisation of vertebrate groups such as fish and larval amphibians. As these aquatic habitats undergo drying and enter states of incomplete recovery, their ecosystem functionality is impacted. We investigated the legacy effects of drying and refilling of wetlands via mesocosms on growth and survival of recolonising aquatic vertebrates and their subsequent effects on ecological function. Specifically, we tested the effects of prior drying on anuran and fish growth and survival (using Gompertz growth curves), the joint effects of vertebrates and drying on periphyton biomass, and whole‐system gross primary productivity. 2. Using 64 1000‐L hard plastic cattle tanks to create replicate aquatic mesocosms, four trophic treatments (no vertebrate control, larval anurans, fish, larval anurans and fish) were crossed with two drying treatments (undried and dried–refilled) to simulate different outcomes of colonisation by two common vertebrate guilds and drying/refilling cycles. Mesocosms with anuran treatments received 50 Lithobates blairi tadpoles (1600 total) and mesocosms with fish treatments received one Lepomis cyanellus juvenile (32 total). We recorded anuran growth rates, survival and time/size at metamorphosis, fish growth, gross primary productivit, and periphyton biomass over 12 weeks from 9 May 2021 to 1 August 2021. 3. Prior drying strongly reduced L. blairi growth rate by 38.2% but increased survival from 48.5 to 75%, resulting in relatively equal emergent anuran biomass between the two drying treatments. No L. blairi survived to metamorphosis when co‐occurring with fish (i.e., larval anurans and fish treatment). On average, prior drying reduced the size at metamorphosis by 35.5%, delayed time to metamorphosis by 4 days, and increased the range of metamorphosis days by 10 days. Fish growth and survival were unaffected by trophic or drying treatments. Gross primary production and periphyton biomass decreased in response to prior drying and the presence of larval anurans, but these effects were non‐constant over time. 4. The effects of short‐term drying were not immediately reversed by refilling and were still perceivable across nearly all trophic levels several months post‐refill. However, for generalist colonisers such as L. cyanellus, optimal habitat is minimally impacted by drying history of the aquatic habitat and depends primarily on the presence of water and connection to source populations. Colonisation by fish removed an entire consumer guild (anuran larvae) and an aquatic–terrestrial flow of resources (anuran juveniles). 5. Climate change is increasing the frequency and severity of droughts and drying events around the world, and increasingly leaving ecosystems in an incomplete state of recovery. Intermittent streams are particularly well‐suited for studying dry–refill cycles as they are one of the most common global freshwater systems. While several studies have investigated the contemporary effects of drying on aquatic systems (i.e., what happens to organisms when a pool dries), this study addresses gaps in our understanding of legacy effects of prior drying on aquatic organisms and ecosystem processes after water returns. Here we clearly show that even short‐term drying has pervasive effects on aquatic ecosystem function following refill. [ABSTRACT FROM AUTHOR]

For the digestion of food, it is important for the gut to be differentiated regionally and to have proper motor control. However, the number of transcription factors that regulate its development is still limited. Meanwhile, the interstitial cells of the gastrointestinal (GI) tract are necessary for intestinal motility in addition to the enteric nervous system. There are anoctamine1 (Ano1)‐positive and platelet‐derived growth factor receptor α (Pdgfra)‐positive interstitial cells in mammal, but Pdgfra‐positive cells have not been reported in the zebrafish. To identify new transcription factors involved in GI tract development, we used RNA sequencing comparing between larval and adult gut. We isolated 40 transcription factors that were more highly expressed in the larval gut. We demonstrated expression patterns of the 13 genes, 7 of which were newly found to be expressed in the zebrafish larval gut. Six of the 13 genes encode nuclear receptors. The osr2 is expressed in the anterior part, while foxP4 in its distal part. Also, we reported the expression pattern of pdgfra for the first time in the larval zebrafish gut. Our data provide fundamental knowledge for studying vertebrate gut regionalization and motility by live imaging using zebrafish. [ABSTRACT FROM AUTHOR]

Ichthyoplankton represent the first life stages of fish. The study of ichthyoplankton is crucial to understanding marine ecosystems and plays an important role in the management and durability of fisheries resources. During March and October of 2019, two oceanographic ichthyoplankton surveys were conducted in the Mediterranean Sea of Morocco from Tanger to Saadia by studying the horizontal structure of the ichthyoplankton species assemblage and its relation to environmental parameters. The average surface water temperature was (15.8°C in spring and 16.4°C in autumn). The fish eggs and larvae were more abundant in March than in October (21268 eggs/10m² and 14084 larvae/10m² in spring and 10094 eggs/10m² and 13796 larvae/10m²). In both seasons, fish eggs from the families Sternoptychidae and Sparidae were dominant (10101 eggs/10m² and 7527 eggs/10m² in spring and 4422 eggs/10m² and 3928 eggs/10m² in fall, respectively). However, Myctophidae larvae were the most abundant in the study area, reaching 7601 larvae/10m² in spring and 11021 larvae/10m² in autumn. The environmental parameters: temperature, salinity and chlorophyll-a (surface) seem to directly influence the spatial distribution of ichtyoplancton. On the other hand, it seems that predation by jellyfish (Pelagia noctiluca)was a very important factor that added to the factors that influenced the distribution of the species of fish eggs and larvae. This work represents the first survey conducted in the southwestern Alboran Sea, which studies the horizontal structure of the ichthyoplankton species assemblage and its relation to environmental factors in the spring and autumn of 2019. [ABSTRACT FROM AUTHOR]

Effective evaluation of technological and operational approaches to reduce entrainment of marine organisms at cooling water intake structures (CWIS) requires accurate organism-sensing systems. Current detection methods lead to large temporal data gaps, require tedious manual analysis, and are fatal to organisms. Here, we describe integrating deep learning with a non-lethal, non-intrusive imaging method—digital holography—to rapidly detect fish larvae. Laboratory experiments demonstrated that the instrument could successfully image fish larvae at flow rates exceeding ranges seen in CWIS. Holograms of two fish larvae species, in the presence of bubbles and detritus, were collected to build a large database for training a lightweight convolutional neural network. The model achieves 97% extraction accuracy in quantifying larvae, and distinguishing them from other particles, including detritus and bubbles, when applied to a dataset of manually classified images, exceeding previous metrics for non-lethal, accurate, and real-time detection. These results demonstrate the potential of in situ holographic imaging for monitoring endangered larval fish species at power plant intake structures, and for high-fidelity, real-time applications in monitoring aquatic ichthyoplankton. [ABSTRACT FROM AUTHOR]

The environmental heterogeneity of the biotopes that compound the mosaic of the rivers is essential for the development of the initial stages of fish life. In this sense, we evaluated the abundance and composition of ichthyoplankton community from different biotopes of the Ibicuí River and its relation with environmental variables, between October 2019 and January 2020. The ichthyoplankton sampling was performed in the Ibicuí River basin, in four biotopes: main river (Ibicuí River), tributary river (Ibirocá River), mouth and lake. Larvae from twenty-nine species were identified, including some threatened with extinction. Eggs and larvae were found in all biotopes, however eggs were more abundant in the main river and larvae in the lake. This last biotope was characterized by the greater presence of larvae in the post-flexion stage and sedentary species. The tributary river had a greater presence of larvae of migratory species. Eggs and yolk-sac larvae were positively correlated with the water speed and river width, while the most developed larvae were correlated with electrical conductivity and zooplankton. Our study revealed that the abundance and diversity of the ichthyoplankton were heterogeneously distributed among the biotopes, where hydrogeomorphological and limnological characteristics enable the emergence of distinct ichthyoplankton assemblages along the river gradient. [ABSTRACT FROM AUTHOR]

This present research characterized the proximate nutrient, fatty acids and amino acids compositions of the wild third instar blowfly larvae collected from fish and chicken wastes as well as its mixture, in view of aquaculture feeding for Asian sea bass (Lates calcarifer). Analyses of crude protein, crude lipids, crude fiber, ash, carbohydrates, amino as well as fatty acids were performed. Results revealed that the larvae that fed on the mixed substrates (chicken and fish, 50:50 ratio) had significantly the highest nutritional values (51.47 ± 0.32% of crude protein, 29.4 ± 1.47% of crude fat, 4.81 ± 0.83% of crude fiber, 4.85 ± 0.01% of ash and 12.71 ± 1.67% of carbohydrate) for formulating feeds for Asian sea bass when compared with that of chicken and fish wastes alone (P < 0.05). Similarly, significantly higher percentages of fatty acids (DHA and EPA) and amino acids (Arg, Lys, Met, Trp, His, Val, Ile, Leu and Phe) were observed in the larvae from mixed-substrates when compared with that of the remaining two substrates (P < 0.05). The findings supported the utilization of blowfly larvae harvested on mixed substrate as a possible candidate of nutrients for Asian sea bass feed formulations. [ABSTRACT FROM AUTHOR]

Being a biologically diversed hotspot in the global marine ecosystem, the Beibu Gulf is inhabited by a high diversity of fish and serves as a vital fishing ground in China. Due to continuous overfishing, the fishery resource has drastically declined in the Beibu Gulf. However, information about the ichthyoplankton assemblages in this area is still lacking. In this present study, ichthyoplankton diversity, spatial and temporal distribution patterns, and assemblage structures were examined using the specimens collected in the late summer–autumn and winter of 2022 in the Beibu Gulf, and the relationship between ichthyoplankton assemblage and environmental variables was studied. A total of 117 ichthyoplankton taxa, belonging to 13 orders and 42 families, were recorded. The most abundant families were Gerreidae, Leiognathidae, and Sillaginidae in late summer–autumn, accounting for 38.74%, 27.95%, and 9.94%, respectively. Sparidae, Platycephalidae, and Sillaginidae were the most abundant families in winter, accounting for 34.03%, 17.15%, and 8.20%, respectively. Cluster analysis identified five assemblages in late summer-autumn and four assemblages in winter. The most characteristic species in each cluster were Terapon jarbua, Sillago sihama, Leiognathus brevirostris, Mene maculate, and Scomberoides tol in late summer-autumn and Scomberomorus commerson, Acanthopagrus latus, Sillago sp., and Evynnis cardinalis in winter. The results of the canonical correspondence analysis indicated that pH, chlorophyll-a (Chl-a), depth, dissolved oxygen (DO), sea surface salinity (SSS), total nitrogen (TN), and total phosphorus (TP) were the major environmental variables affecting the ichthyoplankton assemblage structure in the Beibu Gulf. The finding of this study will provide valuable information in conserving fish spawning grounds and developing fishery management practices to protect fishery resources in the Beibu Gulf. [ABSTRACT FROM AUTHOR]

The Western Channel Observatory (WCO) comprises a series of pelagic, benthic and atmospheric sampling sites within 40 km of Plymouth UK, which have been sampled by the Plymouth Institutes on a regular basis since 1903. This longevity of recording and the high frequency of observations provide a unique combination of data; for example temperature data were first collected in 1903 and the reference station L4 has been sampled on a weekly basis since 1988 where nearly 400 planktonic taxa have been enumerated. While the component datasets have been archived, here we provide the first summary database bringing together a wide suite of the observations. This provides monthly average values of some of the key pelagic and benthic measurements for the inshore site L4 (50° 15.00' N, 4° 13.02' W approx depth 55 m), the offshore site E1 (50° 02.00' N, 4° 22.00' W approx depth 75 m) and the intermediate L5 site (50° 10.80' N 4° 18.00' W approx depth 58 m. In brief, the data include: water temperature (from 1903); macronutrients (from 1934); dissolved inorganic carbon and total alkalinity (from 2008); methane and nitrous oxide (from 2011); chlorophyll a (from 1992); HPLC-derived pigments (from 1999); <20 µm plankton by flow cytometry including bacteria (8 functional groups from 2007); phytoplankton by microscopy (6 functional groups from 1992); microplankton and mesozooplankton from FlowCam (6 groups from 2012), Noctiluca sp. dinoflagellate (from 1997); mesozooplankton by microscopy (8 groups from 1988); Calanus helgolandicus egg production rates (from 1992); fish larvae from Young Fish Trawl survey (4 groups from 1924); benthic macrofauna (4 groups from 2008); demersal fish (19 families from 2008); blue shark, Prionace glauca (from 1958); 16S alpha diversity for sediment and water column (from 2012). These data have varying coverage in time and depth resolution. The metadata tables describe each data set, provide pointers to the source data and other related Western Channel Observatory data sets and outputs not compiled here. We provide summaries of the main trends in seasonality and some major, climate related shifts that have been revealed over the last century. The data are available from Data Archive for Seabed Species and Habitats (DASSH) via the link http://doi.org/10.17031/645110fb81749 (McEvoy and Atkinson, 2023). Making the data fully accessible and including units of both abundance and biomass will stimulate a variety of uptakes. These may include uses as an educational resource for projects, for models and budgets or for analysis of seasonality and long-term change in a coupled benthic-pelagic system and for supporting UK and Northeast Atlantic policy and management. [ABSTRACT FROM AUTHOR]

The larval and post-larval forms of many marine organisms, such as oysters, crabs, lobster, coral, and fish, utilize ambient acoustic cues to orient, settle, or metamorphose. In this study, the effect of anthropogenic and ambient sounds on the orientation behavior of four larval estuarine fishes was examined in a controlled, laboratory experiment. Pre-settlement size red drum Sciaenops ocellatus, southern flounder Paralichthys lethostigma, spotted seatrout Cynoscion nebulosus, and Florida blenny Chasmodes saburrae larvae were exposed to four sound treatments—control, estuarine soundscape, seismic airguns, and large-ship passage—in a linear acoustic chamber. Initial significant (p < 0.05) avoidance of airguns was observed in three of the four species (all but the Florida blenny), but habituation to this sound occurred as the experiment progressed. All species avoided ship passage sounds; however, the avoidance behavior was not significant. Interestingly, none of the species studied were significantly attracted to the acoustic cues alone of the estuarine soundscape; in fact, three of the four species spent less time near the speaker when it was broadcast. These results suggest that larval fish can potentially habituate to anthropogenic noise relatively quickly (<10 min). Understanding how sounds affect larval behavior is necessary because successful recruitment ultimately affects a population's success. [ABSTRACT FROM AUTHOR]

The study of assemblages of fish in their early phases in estuaries is an essential approach to understanding the functioning of these types of ecosystems and their role as nursery grounds for some marine fish species. The main aim of this study was to analyze the ichthyoplankton assemblage in the Bons Sinais Estuary, specifically to clarify the use of this area by species of socio-economic interest. This study identified 22 fish larval taxa among families, genera, and species. Gobiidae (54%), a group of resident species, dominated the community. The larval taxa of socio-economic importance (Thryssa sp., Clupeidae, Sillago sihama, Johnius dussumieri, Pellona ditchela, Pomadasys kaakan, Cichlidae, and Mugilidae) accounted for 23% of the total abundance. Larval density (N°/100 m3) varied spatially and temporally, with higher density and diversity values both in the middle zone and in the wet season. Multivariate analyses revealed that salinity, temperature, and water transparency had a strong influence on larval abundance and density. While most fish larvae were in the post-flexion stage, there was a predominance of pre-flexion larvae in the lower estuary and in the post-flexion stage in the middle and upper zones, especially for marine fish resources, showing the role of this estuarine habitat as a nursery area. [ABSTRACT FROM AUTHOR]

Detection of invasive species is critical for management but is often limited by challenges associated with capture, processing and identification of early life stages. DNA metabarcoding facilitates large‐scale monitoring projects to detect establishment early. Here, we test the use of DNA metabarcoding to monitor invasive species by sequencing over 5000 fishes in bulk ichthyoplankton samples (larvae and eggs) from four rivers of ecological and cultural importance in southern Canada. We were successful in detecting species known from each river and three invasive species in two of the four rivers. This includes the first detection of early life‐stage rudd in the Credit River. We evaluated whether sampling gear affected the detection of invasive species and estimates of species richness, and found that light traps outperform bongo nets in both cases. We also found that the primers used for the amplification of target sequences and the number of sequencing reads generated per sample affect the consistency of species detections. However, these factors have less impact on detections and species richness estimates than the number of samples collected and analysed. Our analyses also show that incomplete reference databases can result in incorrectly attributing DNA sequences to invasive species. Overall, we conclude that DNA metabarcoding is an efficient tool for monitoring the early establishment of invasive species by detecting evidence of reproduction but requires careful consideration of sampling design and the primers used to amplify, sequence and classify the diversity of native and potentially invasive species. [ABSTRACT FROM AUTHOR]

The Pacific Arctic marine ecosystem has undergone rapid changes in recent years due to ocean warming, sea ice loss, and increased northward transport of Pacific‐origin waters into the Arctic. These climate‐mediated changes have been linked to range shifts of juvenile and adult subarctic (boreal) and Arctic fish populations, though it is unclear whether distributional changes are also occurring during the early life stages. We analyzed larval fish abundance and distribution data sampled in late summer from 2010 to 2019 in two interconnected Pacific Arctic ecosystems: the northern Bering Sea and Chukchi Sea, to determine whether recent warming and loss of sea ice has restricted habitat for Arctic species and altered larval fish assemblage composition from Arctic‐ to boreal‐associated taxa. Multivariate analyses revealed the presence of three distinct multi‐species assemblages across all years: (1) a boreal assemblage dominated by yellowfin sole (Limanda aspera), capelin (Mallotus catervarius), and walleye pollock (Gadus chalcogrammus); (2) an Arctic assemblage composed of Arctic cod (Boreogadus saida) and other common Arctic species; and (3) a mixed assemblage composed of the dominant species from the other two assemblages. We found that the wind‐ and current‐driven northward advection of warmer, subarctic waters and the unprecedented low‐ice conditions observed in the northern Bering and Chukchi seas beginning in 2017 and persisting into 2018 and 2019 have precipitated community‐wide shifts, with the boreal larval fish assemblage expanding northward and offshore and the Arctic assemblage retreating poleward. We conclude that Arctic warming is most significantly driving changes in abundance at the leading and trailing edges of the Chukchi Sea larval fish community as boreal species increase in abundance and Arctic species decline. Our analyses document how quickly larval fish assemblages respond to environmental change and reveal that the impacts of Arctic borealization on fish community composition spans multiple life stages over large spatial scales. [ABSTRACT FROM AUTHOR]

Recruitment success of marine fishes is generally considered to be highly dependent on larval growth and survival. In temperate ecosystems, fish larvae are sensitive to food limitation during the low productivity seasons, particularly if water temperatures and concomitant larval metabolic costs increase due to climate change. We combined 7 years of in situ sampling of larval fish, novel observations on zooplankton via automated image analyses, and larval physiological modeling to explore feeding conditions of Atlantic herring larvae (Clupea harengus) in the North Sea. The observed plankton size‐structure was close to the theoretical optimum for larval foraging, but not the biomass. Our results for autumn larvae supported Hjort's critical period hypothesis: small first‐feeding larvae were predicted to have a high probability of starvation, whereas larvae > 13 mm were able to reach their maximal growth capacity. In winter, the majority of herring larvae of all tested sizes (5–27 cm) experienced food‐limitation with over 35% probability of starvation. Sensitivity analysis suggested that young herring larvae improve their growth performance and probability of survival if feed not only on copepods and their life‐stages but include other microplankters in their diet. Given projected warming of the North Sea, our model predicts that herring larvae would require 28% (35%) more prey biomass in autumn (winter) to sustain their growth and survival in the future. This finding together with the ongoing low recruitment of North Sea herring underscore the importance of future micro‐ and mesoplankton monitoring within a scope of wintertime larval fish surveys. [ABSTRACT FROM AUTHOR]

Once hatched, convict surgeon fish larvae (Acanthurus triostegus) spend about two months in the ocean before crossing the coral reef to recruit in the lagoon, usually selecting a specific reef habitat already inhabited by conspecifics. To form groups, juveniles must be able to recognise their conspecifics, even when some have a slightly different morphotype. Here, a virtual reality platform was used that collects juveniles' behavioural reactions to fully immersive controlled visual stimuli. We tested which visual parameters influenced recognition when juveniles had to choose between two virtual shoals of adult convict surgeonfish presented on opposite sides of the aquarium, each with specifically manipulated colour patterns. The results showed that the shape of the adult fish was more important than the patterns and colours for the choice made by the juveniles. These results underline the importance of better understanding the mechanisms of visual recognition in coral reef fish. [ABSTRACT FROM AUTHOR]

The bacterial colonization of newly hatched fish is important for the larval development and health. Still, little is known about the ontogeny of the early microbiota of fish. Here, we conducted two independent experiments with yolk sac fry of Atlantic salmon that were (1) either reared conventionally, with the eggs as the only source for bacteria (egg-derived microbiota; EDM) or (2) hatched germ-free and re-colonized using lake water (lake-derived microbiota; LDM). First, we characterized the gut and skin microbiota at 6, 9, and 13 weeks post hatching based on extracted RNA. In the second experiment, we exposed fry to high doses of either a fish pathogen or a commensal bacterial isolate and sampled the microbiota based on extracted DNA. The fish microbiota differed strongly between EDM and LDM treatments. The phyla Proteobacteria, Bacteroidetes, and Actinobacteria dominated the fry microbiota, which was found temporarily dynamic. Interestingly, the microbiota of EDM fry was more stable, both between replicate rearing flasks, and over time. Although similar, the skin and gut microbiota started to differentiate during the yolk sac stage, several weeks before the yolk was consumed. Addition of high doses of bacterial isolates to fish flasks had only minor effects on the microbiota. [ABSTRACT FROM AUTHOR]

Growing microalgae on vegetable waste (rotten potatoes) media is not only a plausible technique to replace expensive commercial media but also a way of reducing feed costs for rearing zooplankton and fish larvae in aquaculture. As a way of starting an inevitable step up, Monoraphidium littorale was grown in 25% (T1), 50% (T2), and 75% (T3) of digested rotten potato supernatant (DRPS) and at the same time in Bold Basal Medium (BBM) as a control (T4) for 16 days. The highest cell density of M. littorale was recorded in T1, followed by T4, T2, and T3. A similar increasing trend of chlorophyll-a and optical density was also observed during the experimental period. The study also ascertained T1 as a potential growth medium where M. littorale showed superior biomass production which was significantly higher (P < 0.05) than other treatments. It was also worth mentioning that the highest (P < 0.05) protein content was determined in T1 at the end of the cultivation time. Similarly, a highly significant difference (P < 0.05) was also found in the lipid content of the microalgae grown in T1 and T4. Furthermore, the morphology of the cells of M. littorale was found to be strongly affected by the DRPS concentrations and BBM. Thus, the lower concentration of the DRPS served as the best medium for enhancing the growth and biomass of M. littorale. Consequently, to expedite the sustainable progression of microalgal production, cost-effective culture techniques by using different wastes may be adopted. [ABSTRACT FROM AUTHOR]

Simple Summary: The present study analyzed growth priorities during early development in four riverine cyprinid species. The allometric growth of the species studied is in line with the growth pattern typical of many fish species, where high allometric (rapid) growth of head and tail sections is observed at the beginning of the larval period and a clear tendency towards isometric (more balanced) growth at the end of the larval period. It was also observed that a lower level of ontogenetic development of fish after hatching was associated with higher growth rates during the first days after hatching. Specific to the species studied was the absence of abrupt changes in body proportions and the persistence of positive allometric growth in body size throughout the larval and juvenile periods, most likely related to a gradual change in behavior and habitat. Growth patterns during early development of four species of riverine cyprinids, common dace (Leuciscus leuciscus L.), ide (Leuciscus idus L.), chub (Squalius cephalus L.) and common barbel (Barbus barbus L.), over 30 days of rearing, were analyzed. The study period covered three successive phases of larval development (preflexion, flexion, postflexion) and part of the juvenile development. The growth analysis carried out in the present study shows that significant allometric growth occurred mainly in preferentially localized body parts (head and tail) and was also associated with an increase in body height. The replacement of temporary structures (e.g., fin fold absorption) and the appearance of definitive structures around 21 mm TL (beginning of the juvenile period) corresponds to a stabilization of the relative growth of most parts of the body. This is probably due to the fact that the studied species had completed the most important part of the remodeling process (metamorphosis) and had achieved a body shape that allows juveniles to colonize faster water habitats. The results also indicate that individuals of species that are less developmentally advanced at the time of hatching (common barbel, chub) show greater initial dynamics of change in growth rate than individuals of species whose individuals are more advanced in ontogeny (common dace, ide). In addition, the small differences observed in growth parameters between successive periods analyzed, supported by the results of previous studies on these species, probably reflect the lack of abrupt changes in the behavior and habitat of the species studied. [ABSTRACT FROM AUTHOR]

Simple Summary: Microplastics (MPs) contamination is a worldwide problem. Studies have also demonstrated their presence in fish feed, posing serious issues for the aquaculture sector. The present study investigated, for the first time through a comparative approach, the effects of different-sized fluorescent MPs included in a diet intended for zebrafish (Danio rerio). A comparison based on fish developmental stage (larval vs. juvenile), exposure time, and dietary MPs' size and concentration was performed, applying a set of laboratory analyses to elucidate MPs' possible effects on fish growth and welfare, translocation among tissues and organs, and the presence of biological barriers capable of trapping MPs. Results showed that smaller MPs and longer dietary exposure are responsible for translocation of MPs from the gut to other tissues and organs. However, the biological barriers of zebrafish are able to limit MPs' translocation to the muscle. Results obtained in this experimental model are important for possible application to other farmed finfish species. One of the main sources of MPs contamination in fish farms is aquafeed. The present study investigated, for the first time through a comparative approach, the effects of different-sized fluorescent MPs included in a diet intended for zebrafish (Danio rerio). A comparison based on fish developmental stage (larval vs. juvenile), exposure time, and dietary MPs' size and concentration was performed. Four experimental diets were formulated, starting from the control, by adding fluorescent polymer A (size range 1–5 µm) and B (size range 40–47 µm) at two different concentrations (50 and 500 mg/kg). Zebrafish were sampled at 20 (larval phase) and 60 dpf (juvenile stage). Whole larvae, intestine, liver and muscles of juveniles were collected for the analyses. Polymer A was absorbed at the intestinal level in both larvae and juveniles, while it was evidenced at the hepatic and muscular levels only in juveniles. Hepatic accumulation caused an increase in oxidative stress markers in juveniles, but at the same time significantly reduced the number of MPs able to reach the muscle, representing an efficient barrier against the spread of MPs. Polymer B simply transited through the gut, causing an abrasive effect and an increase in goblet cell abundance in both stages. [ABSTRACT FROM AUTHOR]

Amazonian blackwaters are extremely biodiverse systems containing some of Earth's most naturally acidic, dissolved organic carbon -rich and ion‐poor waters. Physiological adaptations of fish facing these ionoregulatory challenges are unresolved but could involve microbially-mediated processes. Here, we characterize the physiological response of 964 fish-microbe systems from four blackwater Teleost species along a natural hydrochemical gradient, using dual RNA-Seq and 16 S rRNA of gill samples. We find that host transcriptional responses to blackwaters are species-specific, but occasionally include the overexpression of Toll-receptors and integrins associated to interkingdom communication. Blackwater gill microbiomes are characterized by a transcriptionally-active betaproteobacterial cluster potentially interfering with epithelial permeability. We explore further blackwater fish-microbe interactions by analyzing transcriptomes of axenic zebrafish larvae exposed to sterile, non-sterile and inverted (non-native bacterioplankton) blackwater. We find that axenic zebrafish survive poorly when exposed to sterile/inverted blackwater. Overall, our results suggest a critical role for endogenous symbionts in blackwater fish physiology. Amazonian blackwaters are acidic and physiologically-challenging, but are one of Earth's most diversified ecosystems. This study revealed that fish survival in these hostile habitats depends on the colonization of their gills by endogenous blackwater Betaproteobacteria, with the potential to regulate host ionoregulatory processes. [ABSTRACT FROM AUTHOR]

Here, I review thermal influences on metabolic rates and aerobic scope; growth; adult body size; and reproductive and behavioural traits, such as tendency and timing of the migration of salmonid fishes. A thermal window bounded by the upper and lower incipient lethal temperatures (UILT and LILT) determines where salmonids can survive. For most salmonids, LILT is close to 0 and UILT is between 20 and 30 °C. UILT and LILT are influenced by the acclimation temperature. Thermal tolerance is affected by fish size and ambient oxygen content, which decreases with increasing temperature. Standard metabolic rate (SMR), the energy required to maintain essential functions, increases with temperature, whereas maximum metabolic rate (MMR) increases with temperature until reaching a peak (pejus). Then, it decreases gradually to zero, i.e., the upper critical limit (TCrit). Aerobic scope (AS = MMR-SMR) reaches its maximum at the pejus temperature. Metabolic rates and aerobic scope can be modified by temperatures that the fish experiences during embryogenesis and possibly also as larvae and young fry. At maximum feeding, maximum growth increases to a point at or below the pejus temperature. The optimum temperature for growth decreases with reduced food intake and increased body size. As for metabolic rate, the growth rate is influenced by the temperature during embryonic development. In a warmer climate, adult body size is expected to decrease chiefly because of a younger age at maturity. Parental fish retained at a higher temperature during maturation produce larger eggs, and this change in egg size may also be transferred to next-generation offspring. Furthermore, embryogenesis in warmer water leads to larger gonad and egg sizes at maturity. Water temperature influences locomotion, foraging and migratory activity. In a warmer climate, juveniles migrate to the sea earlier in spring. In addition, higher embryo temperature leads to delayed return of adult salmon from the ocean. Thus, temperature affects life history traits of salmonid fishes, partly as a direct effect on metabolic rates and food consumption and partly induced as a phenotypically plastic effect. The phenotypically plastic response may preadapt offspring to perform better in the expected future thermal environment. [ABSTRACT FROM AUTHOR]

Eastern boundary systems support major fisheries of species whose early stages depend on upwelling production. However, upwelling can be highly variable at the regional scale, leading to complex patterns of feeding, growth, and survival for taxa that are broadly distributed in space and time. The northern California Current (NCC) is characterized by latitudinal variability in the seasonality and intensity of coastal upwelling. We examined the diet and larval growth of a dominant myctophid (Stenobrachius leucopsarus) in the context of their prey and predators in distinct NCC upwelling regimes. Larvae exhibited significant differences in diet and growth, with greater seasonal than latitudinal variability. In winter, during reduced upwelling, growth was substantially slower, guts less full, and diets dominated by copepod nauplii. During summer upwelling, faster-growing larvae had guts that were more full from feeding on calanoid copepods and relying less heavily on lower trophic level prey. Yet, our findings revealed a dome-shaped relationship with the fastest growth occurring at moderate upwelling intensity. High zooplanktivorous predation pressure led to above average growth, which may indicate the selective loss of slower-growing larvae. Our results suggest that species whose spatio-temporal distributions encompass multiple regional upwelling regimes experience unique feeding and predation environments throughout their range with implications for larval survivorship. [ABSTRACT FROM AUTHOR]

Bacterial populations communicate using quorum‐sensing (QS) molecules and switch on QS regulation to engage in coordinated behaviour such as biofilm formation or virulence. The marine fish pathogen Vibrio anguillarum harbours several QS systems, and our understanding of its QS regulation is still fragmentary. Here, we identify the VanT‐QS regulon and explore the diversity and trajectory of traits under QS regulation in Vibrio anguillarum through comparative transcriptomics of two wildtype strains and their corresponding mutants artificially locked in QS‐on (ΔvanO) or QS‐off (ΔvanT) states. Intriguingly, the two wildtype populations showed different QS responses to cell density changes and operated primarily in the QS‐on and QS‐off spectrum, respectively. Examining 27 V. anguillarum strains revealed that ~11% were QS‐negative, and GFP‐reporter measurements of nine QS‐positive strains revealed a highly strain‐specific nature of the QS responses. We showed that QS controls a plethora of genes involved in processes such as central metabolism, biofilm formation, competence, T6SS, and virulence properties in V. anguillarum, with large strain‐specific differences. Moreover, we demonstrated that the QS state is an important driver of virulence towards fish larvae in one of two V. anguillarum strains. We speculate that infections by mixed‐strain communities spanning diverse QS strategies optimize the infection efficiency of the pathogen. [ABSTRACT FROM AUTHOR]

The freshwater angelfish (Pterophyllum scalare) is a quite popular freshwater ornamental fish in Indonesia due to its distinguished body shape and pattern. However, its growth tends to be slow due to low nutrients in its main diet, namely Daphnia magna. The most feasible solution is to enrich D. magna to increase its nutritional content with Viterna (livestock vitamins). The purpose of this study was to determine the effectiveness of D. magna enriched with Viterna to increase the growth of freshwater angelfish. This study used a Completely Randomized Design to compare three enrichment dosages (10, 20, and 30 ml/L) with a non-enriched control in three replications. This study showed that 3 hours-enrichment can result in an increase in fat (0.6%) and protein (1.25%) profiles in D. magna. Absolute Weight Growth (AWG), Absolute Length Growth (ALG), and Specific Growth Rates (SGR) showed significant differences (P=0.05) between all treatments. The best result was obtained at a Viterna dosage of 30 ml/L which resulted in an Absolute Weight Growth value of 207.14 mg, an Absolute Length Growth of 14.19 mm, and an SGR of 2.58%/day. Survival rates during the larvae culture were not statistically different (P=0.05) among the treatments. Enrichment of D. magna with Viterna has been proven to optimize its potential as live food for fish larvae cultivation. [ABSTRACT FROM AUTHOR]

This study assessed the phenology and functional structure of parental stocks of fish larvae, and evaluated how the species modulate their reproductive activities as a function of natural hydrological regimes in the lower Amazon River, Brazil.Larvae were collected using conical plankton nets monthly over two hydrological cycles between January and December 2013, and between May 2017 and April 2018. The collections were conducted around an alluvial island located near the municipality of Santarém, Pará, Brazil. After identification, individuals were classified into four functional groups (e.g., life‐history strategy, feeding habits, type of migration, and swimming‐performance/microhabitat‐use in the water column) based on species traits. The relationships between seasonal hydrology, environmental variables and larval assemblage structure were evaluated using multivariate analyses.A total of 31,347 fish larvae were collected, from nine taxonomic orders, 26 families, 40 genera and 53 species. The larval assemblages showed highly variable taxonomic and functional composition between different phases of the hydrological cycle (rising water, high water, receding water and low water) and were strongly influenced by environmental variables. Fish reproductive phenology in the lower Amazon is complex and distributed among the hydrological phases. The different ecological characteristics allow the species to withstand specific environmental conditions during each phase.Changes in the structure of larval assemblages indicate that hydrological variability is a key ecological factor influencing the reproductive dynamics of fish and reflects adaptive strategies used to reduce interspecific competition for space and food, maximising recruitment. The variation of fish reproduction across the hydrological cycle that we observed is a result of different ecological characteristics enabling species and functional groups to adapt to environmental conditions of each phase. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are emergent pollutants in freshwater environments and may impact aquatic organisms, including those of nutritional value. The specific activities of digestive and antioxidant enzymes can be used as good bioindicators of the potential effects of MPs on fish in case of waterborne MP contamination. In this study, we used fluorescent polystyrene microplastics (PS-MPs) to analyze the alterations in enzyme activities in larvae of Coregonus peled Gmelin (peled or Northern whitefish), one of the most valuable commercial fish species of Siberia. Our results indicate that peled larvae can ingest 2 µm PS microspheres in a waterborne exposure model. A positive correlation (rs = 0.956; p < 0.01) was found between MP concentration in water and the number of PS microspheres in fish guts, with no significant differences between 24 h and 6-day exposure groups. The ingestion of MPs caused alterations in digestive enzyme activity and antioxidant responses at the whole-body level. The presence of PS-MPs significantly stimulated (p < 0.05) the specific activity of α-Amylase and non-specific esterases in peled larvae after 24 h. However, a pronounced positive effect (p < 0.05) of MPs on the activity of pancreatic trypsine and bile salt-activated lipase was only found after 6 days of exposure compared to after 24 h. Intestinal membrane enzyme aminopeptidase N was also stimulated in the presence of PS-MPs after 6-day exposure. We also observed a significant increase in the specific activity of catalase in peled larvae after 6 days of exposure, which indicates the MP-induced modulation of oxidative stress. Taken together, these results highlight the potential impact of environmental MPs on northern commercial fish, their importance for estimating fish stocks, and the sustainability of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

In order to investigate the species composition and diversity of larvae and juvenile fish in Chongming Dongtan and its surrounding waters, 14 stations were set up in Chongming Dongtan and its surrounding waters from November 2020 to August 2021, and surface horizontal trawling surveys were conducted quarterly with large larvae and juvenile fish nets (diameter 1.3 m, mesh 0.5 mm) for four voyages at each station. A total of 4 556 larvae and juveniles were collected, belonging to 8 orders, 14 families and 48 species. The species composition of dominant species is obvious, of which Coilia mystus (25.09%) was the dominant fish. This was followed by Stolephorus commersonnii (20.12%) and Salanx ariakensis (17.11%). The results showed that the species number and density of larvae and juvenile fishes in spring and summer were significantly higher than those in autumn and winter, and the highest density was 0.658 ind./m³ in summer. The number of species in spring was 28, and the number of species in winter was the least. The species richness index, diversity index and evenness index showed the same trend between seasons, with the highest in spring and the lowest in winter. The density of larvae and juveniles was higher in the north branch than in the south branch in spring and summer, and higher in the south branch than in the north branch in autumn and winter. The results of cluster analysis showed that larvae and juvenile fishes can be divided into freshwater group, estuarine group I and estuarine group II in spring. Summer can be divided into estuarine group and marine group, the larvae and juveniles in Chongming Dongtan of Yangtze River estuary in autumn could be divided into freshwater group, estuarine group and marine group. The species and number of fish larvae and juveniles in winter are very small. Pearson correlation index analysis showed that the richness index, diversity index and evenness index in summer were correlated with salinity, but not with water temperature. The temporal and spatial distribution characteristics of dominant species and communities of larvae and juvenile fish in Chongming Dongtan and the environmental factors affecting their distribution were also discussed. The results will provide important analysis data for the sustainable development and protection of fishery ecological resources in Chongming Dongtan, Yangtze River Estuary. [ABSTRACT FROM AUTHOR]

Fjords play an important role in biological productivity worldwide but are vulnerable to climate/anthropogenic effects. Chilean Patagonia (41°S–55°S) is one of the largest fjord ecosystems in the world, characterized by a complex geography with highly heterogeneous hydrographic conditions and a permanent input from oceanic water mass, both of which influence the ichthyoplankton distributional patterns. In this study, we analysed the distributional patterns of ichthyoplankton and its diversity during austral spring from 1996, 2009 and 2019 in the southern Chilean fjords (47°S–54°S). The area shows important latitudinal gradients of sea surface temperature (from 15°C to 5°C), fjord‐ocean variability in salinity (from 23 to 33) and water column temperature (3°C to 9°C). Spatial (but not temporal) variations in the composition and abundance of ichthyoplankton were recorded, caused mainly by differences in the abundance of larval Sprattus fuegensis, Maurolicus australis and Sebastes oculatus. Richness was higher on continental shelf and the lowest nearby fjord's head and ice fields. At the spatial scale, β‐diversity showed an increased species replacement (turnover) across areas, suggesting an important role of environmental conditions (e.g., salinity and water stratification) on the larval fish structure in this region. Ordination analysis indicates that changes in salinity and temperature, caused by ice melting, is the main environmental factor influencing the abundance of larval Thysanopsetta naresi (1996), Cataetyx messieri (2009) and Bathylagichthys parini (2019). Finally, this study highlights the importance of the conservation and protection of the Chilean Patagonia and monitoring ichthyoplankton communities, which are vital biomarkers of ecosystem health. [ABSTRACT FROM AUTHOR]

Coral reef ecosystems are expected to undergo significant declines over the coming decades as oceans become warmer and more acidic. We investigate the environmental tolerances of over 650 Scleractinian coral species based on the conditions found within their present‐day ranges and in areas where they are currently absent but could potentially reach via larval dispersal. These "environmental envelopes" and connectivity constraints are then used to develop global forecasts for potential coral species richness under two emission scenarios, representing the Paris Agreement target ("SSP1‐2.6") and high levels of emissions ("SSP5‐8.5"). Although we do not directly predict coral mortality or adaptation, the projected changes to environmental suitability suggest considerable declines in coral species richness for the majority of the world's tropical coral reefs, with a net loss in average local richness of 73% (Paris Agreement) to 91% (High Emissions) by 2080–2090 and particularly large declines across sites in the Great Barrier Reef, Coral Sea, Western Indian Ocean, and Caribbean. However, at the regional scale, we find that environmental suitability for the majority of coral species can be largely maintained under the Paris Agreement target, with 0%–30% potential net species lost in most regions (increasing to 50% for the Great Barrier Reef) as opposed to 80%–90% losses under High Emissions. Projections for subtropical areas suggest that range expansion will give rise to coral reefs with low species richness (typically 10–20 coral species per region) and will not meaningfully offset declines in the tropics. This work represents the first global projection of coral species richness under oceanic warming and acidification. Our results highlight the critical importance of mitigating climate change to avoid potentially massive extinctions of coral species. [ABSTRACT FROM AUTHOR]

Copyright of Boletín Científico Centro de Museos de Historia Natural is the property of Universidad de Caldas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The intracohort cannibalism present in tropical gar larvae (A. tropicus) generates great problems in its culture, as in other fish species around the world. The addition of tryptophan (Trp) (10, 20, and 30 g/kg) and a control diet (CD) without Trp were evaluated in A. tropicus larvae regarding growth, survival, cannibalism, behavior, digestive enzymatic activity, and genes related to aggressiveness and/or cannibalism in two stages: 0–13 days after hatching (DAH); and only cannibals (14–24 DAH). In the first stage, no differences were observed in growth parameters; cannibalism was lower with the use of Trp, with the lowest percentage being the 10 g/kg Trp treatment (56.75 ± 2.47%) compared to CD (64.75 ± 1.76%). In the second stage, survival was greater in 10 g/kg Trp (75.00 ± 7.07%) than in CD (23.33 ± 5.77%). Thus, cannibalism was lower with 10 g/kg Trp (20.0 ± 10.0%) compared to CD (76.66 ± 5.77%). Cannibal larvae fed with 10 g/kg Trp had a greater enzymatic activity in acid and alkaline proteases and leucine aminopeptidase, as well as the overexpression of avpi1, crh, and htr1a and the subexpression of tph1, th, sstr1, and hdc (p < 0.05). No aggressive behaviors were recorded in the larvae fed with the 10 g/kg Trp treatment, unlike those fed with CD. The use of 10 g/kg Trp improves survival and reduces cannibalism in A. tropicus larvae.

ABSTRACT: This study evaluated the effect of the co-feeding (C) period on the growth and survival of larvae of the yo-yo loach Botia lohachata ornamental species during the weaning period from live food (LF) to inert food (IF). The breeders were subjected to induced spawning using crude pituitary homogenate. A total of 2,400 larvae were used with an average initial weight of 0.39 ± 0.09 mg and an average total length of 4.08 ± 0.21 mm, from a single breeding pair. The live food was newly hatched nauplii of Artemia franciscana, and the inert diet was a commercial ration with 55% crude protein and two particle sizes (142-350 µm and 350-500 µm). As the first food, all larvae received A. franciscana during the first six days, except for the fasting (NC) and inert food (IF) groups. The following co-feeding strategies were employed: C4 = 4 days of co-feeding, C8 = 8 days of co-feeding, C12 = 12 days of co-feeding, and LF = Artemia during the entire experimental period. The longest period with live food promoted better larval growth rates. The specific growth rate of larvae fed live food during the entire period (LF) was higher than that of the other groups, followed by the co-feeding strategies. There was no effect (P > 0.01) on larval survival in the LF, C12, C8, and C4 groups, which ranged from 41% to 53% after 30 days. Treatment R resulted in high mortality and low growth, suggesting that live food should be the first food source for B. lohachata larvae.

Omnipresent microplastics (MPs) in marine ecosystems are ingested at all trophic levels and may be a vector for the transfer of persistent organic pollutants (POPs) through the food web. We fed rotifers polyethylene MPs (1–4 µm) spiked with seven congeners of polychlorinated biphenyls (PCBs) and two congeners of polybrominated diphenyl ethers (PBDEs). In turn, these rotifers were fed to cod larvae from 2–30 days post-hatching (dph), while the control groups were fed rotifers without MPs. After 30 dph, all the groups were fed the same feed without MPs. Whole-body larvae were sampled at 30 and 60 dph, and four months later the skin of 10 g juveniles was sampled. The PCBs and PBDEs concentrations were significantly higher in MP larvae compared to the control larvae at 30 dph, but the significance dissipated at 60 dph. Expression of stress-related genes in cod larvae at 30 and 60 dph showed inconclusive minor random effects. The skin of MP juveniles showed disrupted epithelial integrity, fewer club cells and downregulation of a suite of genes involved in immunity, metabolism and the development of skin. Our study showed that POPs were transferred through the food web and accumulated in the larvae, but that the level of pollutants decreased once the exposure was ceased, possibly related to growth dilution. Considering the transcriptomic and histological findings, POPs spiked to MPs and/or MPs themselves may have long-term effects in the skin barrier defense system, immune response and epithelium integrity, which may potentially reduce the robustness and overall fitness of the fish. [ABSTRACT FROM AUTHOR]

The genus Thunnus (family Scombridae) comprises eight species of tunas of which all but one are targeted by industrialized fisheries. Although intact individuals of these species can be distinguished by morphological characteristics, researchers and managers often rely on dressed, frozen, juvenile or larval fish samples, which often necessitates the identification of molecular species. Here the authors investigate short amplicon (SA) and unlabelled probe high‐resolution melting analysis (UP‐HRMA) as a low‐cost, high‐throughput molecular genotyping assay capable of distinguishing between albacore tuna (Thunnus alalunga), blackfin tuna (Thunnus atlanticus), bigeye tuna (Thunnus obesus), Atlantic bluefin tuna (Thunnus thynnus) and yellowfin tuna (Thunnus albacares) in the Gulf of Mexico. Although SA‐HRMA of variable regions in the NADH dehydrogenase subunit 4 (ND4) and subunit 5 (ND5), and subunit 6 (ND6) of the mtDNA genome did yield some species‐specific diagnostic melting curves (e.g., ND4 assay can reliably distinguish Atlantic bluefin tuna), genotype masking produced excessive variation in melting curves for reliable multi‐species identification. To minimize the genotyping masking of SA‐HRMA a 26 base pair long UP containing four SNPs was developed within a 133 bp segment of ND4. The UP‐HRMA is able to reliably distinguish Gulf of Mexico species T. thynnus, T. obesus, T. albacares and T. atlanticus by UP melting temperature at 67, 62, 59 and 57°C, respectively. The developed UP‐HRMA assay is a lower‐cost, higher‐throughput, alternative to previously published molecular assays for tuna identification that can be easily automated for large data sets, including ichthyological larval surveys, fisheries specimens lacking distinguishing morphological characteristics or detection of fraudulent trading of tuna species. [ABSTRACT FROM AUTHOR]

Simple Summary: Reports of invasive species have increased dramatically in recent decades, raising public awareness. While human activities favor their spread, global warming is believed to promote the establishment of alien species and pose a major threat to native ecosystems. The freshwater jellyfish Craspedacusta is an example of a globally successful spread, attracting public attention with its short-lived, eye-catching medusa blooms. Two life stages of this jellyfish are predators: the benthic polyps and the planktonic medusae. Both must meet the requirements in their new food webs to become established. We compared their niches with those of presumed native competitors and found a strong overlap for the medusa stage, suggesting high competition with native zooplanktonic predators and young fish. In contrast, the polyps of invasive Craspedacusta and native Hydra differed in their niches, possibly favoring a long-term invasion success of Craspedacusta. When species spread into new regions, competition with native species and predatory–prey relationships play a major role in whether the new species can successfully establish itself in the recipient food web and become invasive. In aquatic habitats, species with a metagenetic life cycle, such as the freshwater jellyfish Craspedacusta with benthic polyps and planktonic medusae, have to meet the requirements of two distinct life stages occurring in two habitats with different food webs. Here, we examined the trophic position of both life stages, known to be predatory, and compared their niches with those of putative native competitors using stable isotope analysis. We found that δ13C and δ15N signatures of medusae overlapped with those of co-occurring Chaoborus larvae and juvenile fish (Rutilus rutilus) in a well-studied lake, implying high competition with these native predators. The comparison of δ15N signatures of Hydra and Craspedacusta polyps in four additional lakes revealed their similar trophic position, matching their predatory lifestyle. However, their δ13C signatures differed not only across all four of the lakes studied but also within one lake over time, suggesting a preference for pelagic or benthic food sources. We conclude that invasive and native polyps differ in their niches due to different food spectra, which favors the invasion success of Craspedacusta. [ABSTRACT FROM AUTHOR]

First feeding of many fish larvae depends on live feed. A comparative investigation on the effectiveness of different types of live feed is not available to our knowledge. Hence, we conducted a study to examine the effect of different types and combinations of live feed on the performance (survival rate, total length, body width, body mass, malformation rate) of pikeperch, Sander lucioperca, larvae. From day 0 (onset of exogenous feeding) to day 10, the saltwater rotifer Brachionus plicatilis, the freshwater rotifer Brachionus calyciflorus, the ciliate Paramecium bursaria, copepods (nauplii and copepodites) from a lake population, and Artemia nauplii were tested. Feeding with B. plicatilis, B. calyciflorus, and P. bursaria resulted in high survival rates of 80% and a homogenous and significant growth (increase in total length of 50% and in body width of 20%). As follow-up feed, copepod nauplii and Artemia nauplii were tested from day 11 to day 20. Copepod nauplii were superior to Artemia nauplii, as larvae fed with copepods showed higher survival rates (67–70% versus 38–47%) and a more homogeneous growth. A switch from seawater live feed to freshwater live feed or vice versa resulted in decreased survival rates. Therefore, a feeding regime consisting of B. calyciflorus or P. bursaria followed by copepods is considered optimal as first feed of pikeperch. The malformation rate was not affected by the tested feeding regimes. To investigate the wider applicability and transferability of these findings, complementary investigations were performed on burbot, Lota lota, and the freshwater whitefish Coregonus atterensis. The feeding regimes used for S. lucioperca larvae were also suitable for Lota lota. Moreover, L. lota could be fed with lake copepods from the onset of exogenous feeding. For C. atterensis, initial feeding with B. plicatilis, B. calyciflorus, or P. bursaria had no positive effects. Feeding with copepods from the onset of exogenous feeding was optimal considering survival rate and growth. Therefore, optimal first feeding regimes are very species specific and should be established for each new species. [ABSTRACT FROM AUTHOR]

The Ohio River Ecological Research Program (ORERP), sponsored by multiple power plants along the river's main stem, was in existence for 50 years. Its goals were to collect fish community data to evaluate possible impacts to Ohio River fish communities because of either power plant discharges (i.e., thermal effects) or cooling water intakes. Studies by the ORERP have shown that thermal avoidance of discharge areas often occurs during the summer, but this avoidance is temporary and reversible, and long‐term disruptions of the fish communities have not been detected. Impingement studies conducted at 13 plants from 2005 to 2007 showed that impingement was highly episodic and dominated by clupeids and Freshwater Drum Aplodinotus grunniens. Impinged fish were mainly (>90%) young of the year; as a result, impingement numbers strongly reflected year‐class strength. Entrainment of ichthyoplankton was conducted under the ORERP at seven plants in 2015 and 2016. Annual entrainment estimates ranged from 43 million to 3.5 billion (i.e., 3.5 × 109) ichthyoplankton depending on the plant. The principal benefit of this collaborative effort was that these data allowed the sponsoring facilities and others to access an extensive database upon which fact‐based regulatory, resource management, and plant operating decisions could be based. Most importantly, the ORERP is a collaborative model for private and public organizations to collect, share, and analyze data and make resource management decisions for a large, multi‐use aquatic resource. [ABSTRACT FROM AUTHOR]

Invasive species constitute a threat not only to native populations but also to the structure and functioning of entire food webs. Despite being considered as a global problem, only a small number of studies have quantitatively predicted the food web‐level consequences of invasions. Here, we use an allometric trophic network model parameterized using empirical data on species body masses and feeding interactions to predict the effects of a possible invasion of Amur sleeper (Perccottus glenii), on a well‐studied lake ecosystem. We show that the modeled establishment of Amur sleeper decreased the biomasses of top predator fishes by about 10%–19%. These reductions were largely explained by increased larval competition for food and Amur sleeper predation on fish larvae. In contrast, biomasses of less valued fish of lower trophic positions increased by about 0.4%–9% owing to reduced predation pressure by top piscivores. The predicted impact of Amur sleeper establishment on the biomasses of native fish species vastly exceeded the impacts of current‐day fishing pressures. [ABSTRACT FROM AUTHOR]

Fish skeletal development has long been correlated with nutritional factors. Lack of zebrafish nutritional standardization, especially during the early stages, decreases the reproducibility of the conducted research. The present study represents an evaluation of four commercial (A, D, zebrafish specific; B, generic for freshwater larvae; C, specific for marine fish larvae) and one experimental (Ctrl) early diets on zebrafish skeletal development. Skeletal abnormalities rates in the different experimental groups were assessed at the end of the larval period (20 days post‐fertilization, dpf) and after a swimming challenge test (SCT, 20–24 dpf). At 20 dpf, results revealed a significant effect of diet on the rate of caudal‐peduncle scoliosis and gill‐cover abnormalities, which were relatively elevated in B and C groups. SCT results focused on swimming‐induced lordosis, which was comparatively elevated in diets C and D (83% ± 7% and 75% ± 10%, respectively, vs. 52% ± 18% in diet A). No significant effects of dry diets were observed on the survival and growth rate of zebrafish. Results are discussed with respect to the deferential diet composition between the groups and the species requirements. A potential nutritional control of haemal lordosis in finfish aquaculture is suggested. [ABSTRACT FROM AUTHOR]

Objective: Regulatory legislation in both the United States and Canada requires water users with medium to high intake volumes to monitor entrainment losses to determine effects and to assess potential mitigation strategies to reduce harm to fish. Recent studies have recommended the use of both increased sampling frequency and sampling volume to characterize fish entrainment for large power plants on the Great Lakes. There is little doubt that increasing the flow rate and volume of water collected for sampling reduces the uncertainty in estimates of annual entrainment. Depending on the type of pump and the pumping flow rate used for entrainment sampling, considerable damage to fish larvae can occur. A screw‐type centrifugal pump has many qualities that make it ideal for entrainment sampling, but it has not yet been used as a sampling device for fish entrainment applications at power plants or other large industrial water users. The objective of this study was to determine mortality of entrainable fish eggs and larvae due to passage through a screw‐type centrifugal pump. Methods: In a laboratory setting, Lake Trout Salvelinus namaycush eggs and larvae, Lake Whitefish Coregonus clupeaformis eggs, and Rainbow Trout Oncorhynchus mykiss juveniles were passed through a screw‐type centrifugal pump at three treatment flow rates: 39.5, 47.3, and 59.1 m3/h. Fish and eggs were monitored for mortality posttreatment and again at 24 and 48 h. Result: Across treatments, very few mortalities were observed. Species specific moralities were four larval Lake Trout, one Lake Whitefish egg, and one juvenile Rainbow Trout. No mortality was observed for Lake Trout eggs. Conclusion: The present study identified high egg and larval survival (≥99%) after passage through a screw‐type centrifugal pump. High survival reduces error associated with identification and counting of entrained organisms, which provides more accurate estimates of annual entrainment losses. Impact statementA screw‐type centrifugal impeller pump results in high survival of entrainable fish (eggs and larvae), which reduces error associated with estimating fish mortality due to entrainment. Reduced error improves entrainment mortality estimates that may be used to develop compensation strategies to mitigate loss of fish from aquatic systems. [ABSTRACT FROM AUTHOR]

The estimated biomass of mesopelagic fishes has been revised recently, indicating the importance of their roles in oceanic ecosystems and global biogeochemical cycling. This study clarified the occurrence patterns of larval mesopelagic fish species in the surface layers of the highly eutrophic Tokyo Bay. Oceanographic observations and larval fish sampling were conducted across four seasons in 2003 and 2005–06 from the inner area to the mouth of the bay. The number of mesopelagic fishes sampled was 2,276 individuals of 78 species (14 families), accounting for 0.4% of total specimens and 25.4% of the total species number. Myctophidae comprised the largest number of species, with 43 species/morphotypes, followed by Gonostomatidae (seven species). Most larvae in Tokyo Bay were found to belong to tropical/subtropical species. The number of mesopelagic species was negatively correlated with the distance from the Kuroshio Current axis to the mouth of the bay, suggesting that these species were transported by the Kuroshio Current. A thermohaline front likely functions as a barrier preventing mesopelagic fish larvae from entering the inner bay area. Species in the outer bay and mouth of the bay clearly differed, likely due to the differing vertical distributions innate to each species. On the other hand, some species occurred in surface layers penetrated by inner bay water. In addition, the abundances of a myctophid species and copepods, which are potential food items for larvae, were positively correlated, suggesting that some mesopelagic larvae actively approach productive coastal waters due to the advantage of food availability. [ABSTRACT FROM AUTHOR]

Inshore habitats play a crucial role in the downstream drift of larval fish in large rivers. Natural inshore habitats of most of the world's large rivers have been heavily degraded by shoreline stabilization measures, but the knowledge about consequences for the condition and distribution of larval fishes is extremely limited. Investigations during the peak season of larval drift into species composition as well as into feeding intensity and body injuries of representative taxa were conducted at different inshore mesohabitats along semi‐natural and stabilized shores in a free‐flowing section in the middle Yangtze River. Species were unambiguously identified by a combination of DNA barcoding and morphological analyses. Overall, 37 taxa from seven families were detected from a total of 9,915 fish larvae caught. Earlier developmental stages greatly outnumbered the later stages in diversity and abundance in each investigated mesohabitat. Abundance and assemblage structure as well as the body injury rate differed significantly between mesohabitats. Generally, overall species richness and abundance tended to be lower, and divergence of the assemblage and body injury rates tended to be higher at heavily hardened shores, which could be contributed to the poor riparian vegetation and restricted suitable hydraulic conditions there. Our results may reflect the underestimated impact of inshore habitat degradation on larval fishes and highlight the demand for creating adequate areas of shallow and slow‐flow habitats with good riparian vegetation conditions along the shores. These measures will foster an appropriate connectivity between spawning areas and high‐quality nurseries for larval fishes. [ABSTRACT FROM AUTHOR]

In recent decades, there has been a growing interest in modeling spatial–temporal data, which can be found in many fields including geoscience, meteorology and ecology, among many others. The spatial–temporal dependence structure modeling, using a random field approach, is an indispensable tool to estimate the parameters that define this structure. However, this estimation may be greatly affected by the presence of atypical observations in the sampled data. Our proposal is to extend the results of Uribe-Opazo et al. (J Appl Stat 39:615–630, 2012) and De Bastiani et al. (Test 24:322–340, 2015) in the studies of diagnostic techniques to assess the sensitivity of the maximum likelihood estimators to small perturbations in the response variable for the spatial–temporal linear models with separable covariance. The method's viability is illustrated in a simulation study, and in an application to eggs anchovy (Engraulis ringens) abundance data in ichthyoplankton surveys from the northern zone of Chile. The results show that the proposed methodology allows to detect influential observations in a spatial-temporal data set when their covariances are separable. [ABSTRACT FROM AUTHOR]

The northern coast of the Iberian Peninsula is an important spawning and nursery area for several marine fish species, some of which are economically exploited by fisheries and under management plans. Larval stages of fish are highly sensitive to environmental change and anthropogenic pressures, and Marine Protected Areas (MPA) can help mitigate the impacts on fish populations. This study investigated the environmental drivers of the temporal and spatial patterns of the larval fish assemblages inhabiting a small coastal MPA along the NW Portuguese Iberian Coast. Seasonal surveys were conducted over two years at nine sampling stations distributed throughout the MPA to collect larval fish samples and water parameters. Results showed that a total of 39 different fish taxa were identified. In terms of abundance, reef-associated species, such as Parablennius gattorugine (54.6%), and marine species that use estuaries as nursery areas, such as Ammodytes tobianus (15.7%) and Clupeidae n.i. (8.8%) dominated the larval fish assemblages. The larval fish assemblages were characterized by a strong temporal pattern that, according to CCA analyses, was related to the temporal variability of water temperature, pH, chlorophyll α, TPM, and also the river flow of an adjacent river. This study showed that 47% of the fish larvae belonged to commercially exploited species, highlighting the importance of this MPA as a nursery area for the early life stages of the fish population. Overall, these new findings emphasize the role of MPAs in ensuring the connectivity of fish species between marine-estuarine habitats and enhancing the conservation of fish populations. [ABSTRACT FROM AUTHOR]

Striped catfish Pangasianodon hypopthalmus (Sauvage, 1878) is a flagship catfish species of the Mekong River region, a commercially valuable food fish that is important in freshwater fisheries, and a popular aquaculture species in many Asian countries. The species was assessed as "Endangered" by the International Union for Conservation of Nature (IUCN) due to range contraction and declining abundance, though the status of the species' wild population in Cambodia, a critical habitat for the species, is not well understood. Here, we assess the population status of the striped catfish in Cambodia using multiple sources, including time-series catch data and length frequency distribution data from a commercial fishery (stationary trawl bagnet or dai) operated in the Tonle Sap River from 1998/99 to 2017/18 and larval drift data monitored in the Mekong River in Phnom Penh from 2004 to 2018. We found that there was a significant decline (R2 = 0.54, p = 0.0002) in the catch (metric tonnes) of the striped catfish from the commercial dai fishery over the last two decades. Similarly, length-based indicator analysis indicates that striped catfish mean length and abundance have both declined over the study period, raising concerns about the sustainability of river catfish fisheries. Moreover, long-term larval drift monitoring in Mekong River shows that there was a marginally significant decline in the quantity of striped catfish larvae/juvenile drifting downstream to the lower floodplain over the last decade. Changes in flood index (extent and duration of flood) in the Tonle Sap floodplain affected by the Mekong's flow are likely key factors driving the decline of the wild populations of the striped catfish. Both larval fish abundance and floodplain fish harvests have a significant positive relationship with Mekong flow and flood extent. Indiscriminate fishing exacerbates pressures on striped catfish stocks. Therefore, actions such as maintaining natural seasonal flows (flood timing, extent, and duration) to the Tonle Sap floodplain and protecting migratory fish stocks from overharvest and habitat fragmentation are essential to the persistence of stocks of striped catfish and other large-bodied migratory fishes that utilize both the Cambodian Mekong and Tonle Sap floodplains. [ABSTRACT FROM AUTHOR]

Thiamine is a crucial nutrient in larval stage of fish, and thus, the present study aimed at evaluating the effects of dietary thiamine supplementation on survival, growth performance, and biochemical parameters of beluga, Huso huso, larvae. The fish larvae (50 ± 4.5 mg) were fed diets containing 0 (control), 5, 10, and 20 mg/kg thiamine for 26 days from 18 days after hatching to 44 days after hatching. Thiamine significantly increased the larvae survival, growth rate, digestive enzymes activity, and whole body protein and ash but decreased the whole body lipid and moisture P < 0.001 ). Also, alanine amino transferase (ALT) and alkaline phosphatase (ALP) were decreased significantly in thiamine-treated groups (P < 0.05). The highest survival and whole body ash were observed in 20 mg/kg thiamine treatment; the highest whole body protein and lipase activity were observed in 10 mg/kg thiamine treatment. The highest growth rate, amylase, and lowest whole body lipid, alanine amino transferase (ALT), and alkaline phosphatase (ALP) were observed in 10 and 20 mg/kg thiamine treatments. All thiamine-treated fish exhibited similar pepsin and chymotrypsin activities, all above the control fish. There were no significant effects of dietary thiamine supplementation on trypsin, whole body lysozyme, alternative complement (ACH50), lactate dehydrogenase (LDH) activities, and IgM levels. According to the results, 10–20 mg/kg dietary thiamine supplementation can increase the performance of beluga larvae by improving the health of liver and the activity of digestive system. [ABSTRACT FROM AUTHOR]