Search

Invasive species present a serious peril to aquatic ecosystems worldwide, thus it is essential to have a comprehensive understanding of the reproductive dynamics, spreading characteristics, and biological properties of these species in order to effectively manage their population structure and mitigate both the ecological damage and economic loss they can cause. For this reason, we delved into the reproductive dynamics of Pseudorasbora parva, an invasive species of inland water fish found in Türkiye. We focused on three populations inhabiting Beyşehir (Konya, Isparta) and Eğirdir Lakes (Isparta) and Onaç Reservoir (Burdur). Sampling was carried out on a monthly basis from March 2021 to June 2022, utilizing a variety of tools such as multimesh nets, seine nets, and electrofishing. The developmental stages of gonads and reproductive cells were determined through morphological and microscopic examinations. A total of 1186 P. parva individuals were captured from all three lakes. Our results showed that the Beyşehir Lake population spawned from March to July, while the Eğirdir Lake population did so between May and October, and the Onaç Reservoir population laid their eggs from June to August. Female individuals in Beyşehir Lake, Eğirdir Lake, and Onaç Reservoir had initial breeding lengths of 3.49, 4.89, and 5.35 cm, respectively. In comparison, male individuals measured 5.56, 4.80, and 5.40 cm. Interestingly, the Beyşehir Lake population exhibited the highest egg fecundity, with each individual at 2 years producing a remarkable 2949 eggs. The present findings provide valuable information for us to further understand the reproductive biology and dynamics of P. parva, which could be useful in managing and preventing the spread of this invasive species in inland aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The objective of this study is to provide information on the reproductive biology of tomato hind grouper, Cephalopholis sonnerati (Valenciennes, 1828) for conservation and management purposes. Fish caught by artisanal fishermen from September 2019 to August 2021 were analysed. A total of 280 females, 31 males, and 4 transitional and 178 sex‐undetermined fish were analysed. The female to male sex proportion was 9:1, and the fish reached a maximum total body length of 38.5 and 54.5 cm for females and males, respectively. The following microscopic stages were identified: immature, developing, ripe, running ripe/releasing, and spent in both males and females. Several asynchronous development patterns were observed in the studied gonads, including multiple oocyte stages and early and advanced stages of sexual transition. High gonadosomatic index (GSI) for both males and females was recorded in March, May, and November. Running ripe and releasing stages in females were identified in the months from March to June, which indicates the spawning season. The absolute and relative fecundity of the species ranged from 162,723 ± 207,267 and 239 ± 285, respectively. An exponential relationship was found between fecundity and total body length (TL), fecundity and total body weight (TW), and fecundity and gonad weight (GW). [ABSTRACT FROM AUTHOR]

This study was the first to investigate the key reproductive traits of the electric lantern fish Electrona risso (Myctophidae, n = 918) and the bigscale fishes (Melamphaidae) Melamphaes polylepis (n = 260) and Scopelogadus mizolepis (n = 649). Specimens of these mesopelagic species were collected in March and April 2015 in the eastern Central Atlantic (0–24° N, 20–26° W). Sex ratio was not significantly different from 1:1 in E. risso and M. polylepis but significantly skewed toward female dominance in S. mizolepis. Reproductive phases were determined macroscopically and by histological analyses on selected individuals. Female length at 50% maturity (L50) was 55.1 mm standard length (LS) in E. risso, with an observed female maximum length (Lmax) of 81.2 mm LS. M. polylepis females had an L50 of 40.2 mm LS and an Lmax of 86.7 mm LS. S. mizolepis had an L50 of 46 mm LS and an Lmax of 97.9 mm LS. The three species show histological features of iteroparity, but the E. risso population appears to occur in two year‐classes and experience only one spawning season per lifetime in the study region. All three species are batch‐spawners. A batch fecundity of 2668 eggs was estimated from one E. risso individual, with a relative batch fecundity of 369 eggs g−1 gonad‐free body mass. M. polylepis had a batch fecundity of 1027 eggs and a relative batch fecundity of 149 eggs g−1 (n = 3). S. polylepis had a batch fecundity of 1545 eggs and a relative batch fecundity of 215 eggs g−1 (n = 21). The median gonado‐somatic index during the actively spawning phase of E. risso was 4.5, significantly lower than that of M. polylepis (7.5) and S. mizolepis (7.1). No regressing or regenerating phases were observed in this study. Batch‐spawning in all three species is suggested to be advantageous to cope with intra‐annual variability in food supply and other risks for offspring survival. With what appears to be in effect a (facultative) semelparous strategy in combination with a short life span in E. risso, interannual differences would have a great effect on population dynamics of this species. Knowledge is still lacking on temporal aspects of reproduction such as the duration of the spawning season and the frequency of spawning, as well as age and growth. [ABSTRACT FROM AUTHOR]

Schizothorax plagiostomus, commonly known as snow trout, is a popular food fish found in parts of Central Asia and the Indo‐Himalayan region. Despite such a broad range of distribution and potential financial value, it is a highly neglected cold‐water ichthyofauna. Furthermore, an alarming decline in Schizothoracine population has been reported in the recent past due to climate change and uncontrolled anthropogenic interference. In this study, the seasonal variations in ovarian architecture and development were examined in adult S. plagiostomus from Garhwal Himalayan region, Uttarakhand, India. Ovarian‐somatic index ranged from 16.86 ± 0.29 to 0.31 ± 0.56, with a maximal value in September and a minimal value in April. Ovarian histology revealed the abundance of primary growth oocytes in resting and preparatory stages; primary/secondary vitellogenic oocytes with numerous cortical alveoli were predominant in the developing stage of pre‐spawning ovaries; secondary/tertiary vitellogenic oocytes were conspicuous in actively spawning ovaries; and atretic follicles/oocytes were discernible during the regressing stage of spent ovaries. Scanning electron microscopy of mature ova (mean diameter 2.003 ± 0.01 mm) prominently showed the structure micropyle (mean diameter 12.93 ± 3.38 μm). Fecundity analyses suggested that September was the principal breeding season, whereas residual spawning occurred with fresh rain in late winter during February–March. Collectively, this is the first comprehensive qualitative and quantitative report of the seasonal variations in the ovarian development and function for S. plagiostomus. These data may provide valuable information towards the captive breeding programme as well as conservation and management for Schizothoracine fishes in normal and altered climatic conditions. [ABSTRACT FROM AUTHOR]

Although oogonial proliferation continues in mature females in most teleosts, its dynamics and the transformation of oogonia to early meiotic oocytes during the reproductive cycle have received little attention. In the present study, early oogenesis was examined throughout the reproductive cycle in two Clupeiform fishes, the Mediterranean sardine, Sardina pilchardus, and the European anchovy, Engraulis encrasicolus. Observations using confocal laser scanning microscopy (CLSM) provided extensive information on markers of oogonial proliferation (mitotic divisions, oogonia nests) and meiotic prophase I divisions of oocyte nests (leptotene, zygotene, pachytene, diplotene) in ovaries of different reproductive phases. In sardine, oogonial proliferation persisted throughout the entire reproductive cycle, whereas in anchovy, it was more pronounced prior to (developing ovaries) and after (resting ovaries) the spawning period. Anchovy exhibited a higher rate of meiotic activity in developing ovaries, whereas sardine exhibited a higher rate in resting ovaries. The observed differences between the two species can potentially be attributed to different seasonal patterns of energy allocation to reproduction and the synchronization between feeding and the spawning season. [ABSTRACT FROM AUTHOR]

The reproductive fitness of female European eels (Anguilla anguilla L.) from the Warnow River, Germany, Baltic Sea region, was evaluated by estimating fecundity and applying a spawning model. Individual fecundity ranged from 1,440,000 to 7,455,000 oocytes and mean relative fecundity equalled 5,956,015 oocytes kg−1. Modelling suggests that 43% of eels hold insufficient energy storages or are within 10% of complete depletion. The fraction of eels with insufficient energy supply increases from 19% to 35% if the effect of parasitic infection is considered. [ABSTRACT FROM AUTHOR]

Empirical evidence for increases in the reproductive potential (egg output per unit area) of coral reef fish in no‐take marine reserves (NTMRs) is sparse. Here, we inferred the development of reproductive potential in two species of protogynous reef fishes, Chlorurus bleekeri (Labridae: Scarinae) and Cephalopholis argus (Epinephelidae), inside and outside of Philippine NTMRs. We estimated key reproductive parameters and applied these to species‐specific density and length data from 17 NTMRs (durations of protection 0–11 years) and paired fished sites (controls) in a space‐for‐time substitution approach. For C. argus, we also used density and length data collected almost annually over 29 years from a NTMR and an adjacent control at Apo Island. The results suggest that C. bleekeri can develop 6.0 times greater reproductive potential in NTMRs than controls after 11 years of protection, equivalent to approximately 582,000 more eggs produced 500 m−2 inside NTMRs. Enhancement of reproductive potential in C. argus was not evident after 11 years in the space‐for‐time substitution. At Apo Island NTMR, reproductive potential of C. argus increased approximately 6‐fold over 29 years but NTMR/control ratios in reproductive potential decreased through time (from 3.2 to 2.4), probably due to spillover of C. argus from the NTMR to the control. C. argus was estimated to produce approximately 113,000 more eggs 500 m−2 inside Apo Island NTMR at the 29th year of protection. Ratios of reproductive potential between NTMR and controls in C. bleekeri and C. argus were often greater than corresponding ratios in density or biomass. The study underscores the importance of species‐specific reproductive life history traits that drive variation in the development of larval fish subsidies that originate from NTMRs. [ABSTRACT FROM AUTHOR]

The depletion and overexploitation of several fish stock demands for a valorisation of non‐target and discarded species. Nonetheless, such species are often poorly studied, and information on their biological parameters must be gathered for effective population management. For 1 year, the reproductive strategy of the piper gurnard Trigla lyra and the red gurnard Chelidonichthys cuculus was studied by monthly samples obtained from commercial boats operating on western Portuguese coast. Both species showed a biased sex ratio towards females, especially for larger length classes. Length at first maturity could be estimated only for red gurnard (22.1 and 19.9 cm for females and males, respectively) because all piper gurnard individuals caught were mature. Piper gurnard showed determinate fecundity and a short spawning season, from November to February with a peak in January, whereas red gurnard showed indeterminate fecundity and a wide spawning season, from late December to May. The relative annual fecundity estimated for red gurnard (1893 ± 728 oocytes × g−1 eviscerated weight [EW]) was higher than the one estimated for piper gurnard (1018 ± 250 oocytes×g−1 EW). Although important information for understanding the species dynamics is presented in this study, additional information on other life‐history parameters and of species landings is required. [ABSTRACT FROM AUTHOR]

The reproductive biology of Pacific hagfish Eptatretus stoutii (Lockington, 1878) and black hagfish Eptatretus deani (Evermann & Goldsborough, 1907) was assessed using current and historical data. Our results found that the reproductive characteristics of both hagfish species reflect those of K‐selected species, which tend to live long and exhibit slow growth rates, low fecundity (approximately 20 eggs per female) and late maturity. Additionally, females of both species commence maturation prior to males. This study provides a population profile for both species of hagfish, but further assessments are needed to effectively manage a sustainable hagfish fishery. [ABSTRACT FROM AUTHOR]

Hardhead catfish Ariopsis felis are a common marine catfish in the coastal waters of the Gulf of Mexico (GOM). The low economic value of this species has depressed interest and research, and although the species is known for its extremely low fecundity and large oocytes, little else is known about this catfish species. A total of 1230 samples across all months of the year from 2016 to 2018 resulted in 681 females, and analysis of gonado‐somatic index (IG) revealed 1% to be a clear cut‐off indicating maturity. Females are considered capable of spawning from April to June when IG averaged 4–8%. Both atresia and post‐ovulatory follicles were present in July, suggesting that spawning ends in July in the northern GOM. The 1% IG cut‐off was used to designate maturity, and from that an L50 of 253 mm was estimated. Batch fecundity from 41 females estimated a mean batch size of 36 oocytes. Perhaps the most interesting finding was the presence of secondary growth stage oocytes (e.g., cortical alveoli) from July through November, well outside the spawning capable period. Furthermore, 78% of females had some early vitellogenic oocytes present during the non‐spawning season, and the distribution of these relatively large (2–5 mm) oocytes did not change over time. The results here are not only important as reproductive biology information for a common and abundant species, but also present interesting and unusual patterns of non‐spawning season oocyte development that is not commonly seen in Western Hemisphere subtropical fish species. [ABSTRACT FROM AUTHOR]

The present study examined temporal changes in plasma sex hormone concentrations and the morphology and histology of reproductive organs in mature northwest Atlantic (NWA) bonnetheads Sphyrna tiburo L. to characterize reproductive cycle, breeding periodicity and fertility in this still poorly studied population. Progressive increases in testis width, epididymis head width, plasma testosterone (T) concentrations, and occurrence of mature spermatozoa were observed in male S. tiburo from June to September, demonstrating that spermatogenesis occurs during the summer. Nonetheless, increases in maximum follicle diameter, oviducal gland width, plasma 17β‐estradiol and T concentrations, and occurrence of vitellogenic follicles were not observed in mature females until between October and April, demonstrating non‐synchronous patterns of gametogenesis in males and females. Fresh copulatory wounds were observed in females collected during late September along with histological evidence for sperm presence in the oviducal gland between September and April, confirming a 6‐ to 7 month period of female sperm storage. Ovulation occurred between mid‐April and early May in concert with increases in female plasma progesterone concentrations. Gestation occurred during a 4.5‐ to 5 month period between May and early September, and 97% of mature females collected during this period were gravid, indicating a highly synchronized, annual reproductive periodicity. Brood size was significantly correlated with maternal size and ranged from 1 to 13 pups with a mean ± S.D. of 8.1 ± 2.2, which was significantly lower than reported in Gulf of Mexico (GOM) populations. The occurrence of non‐fertile offspring was observed in 17% of broods with a range of 1–7 non‐fertile eggs present in individual females. Thus, as previously reported in GOM S. tiburo, this unusual form of infertility also appears to be prevalent in the NWA population and requires further study. This study has demonstrated meaningful differences in reproductive biology of these populations, emphasizing the need for region‐specific approaches for population management. [ABSTRACT FROM AUTHOR]

To provide updated information on life history for improved fishery management, the reproductive cycle of the finetooth shark Carcharhinus isodon from Northwest Atlantic (NWA) populations was investigated by examining temporal changes in morphology and histology of reproductive organs. Changes in plasma concentrations of gonadal sex hormones in relation to reproductive stage were also examined. Increases in testis width, epididymis head width, plasma testosterone concentrations and occurrence of mature spermatozoa were observed in male sharks between December and April, suggesting a seasonal pattern in reproduction that culminates with copulatory activity in May. Increases in maximum follicular diameter, oviducal gland width, plasma 17β‐estradiol concentrations and occurrence of vitellogenic follicles were observed in non‐pregnant female sharks during the same time period along with the occurrence of newly pregnant females in May, demonstrating strong synchronicity between male and female reproductive cycles. Pregnant females bearing full‐term embryos were also observed in May, indicating that parturition occurs between mid‐May and early June and gestation requires 12 months. Only transient temporal changes in follicle size and oviducal gland width were observed in pregnant females, indicating that reproductive periodicity is biennial; nonetheless, a single female exhibiting signs of concurrent vitellogenesis and pregnancy was observed. Mean brood size ± S.D. was 3.9 ± 0.9 offspring/female. Fecundity was not significantly correlated with female size, in part due to an unexpectedly high rate of early embryo mortality, which occurred in 11% of pregnant females, and was more common in larger individuals. Changes in ovarian activity during mid‐pregnancy were observed, suggesting possible roles for the ovary in regulating some aspects of early to mid‐gestation. This study confirms that earlier characterizations of the reproductive cycle and fecundity in NWA finetooth sharks remain valid for use in fishery management. This study also highlights unusual features of finetooth shark pregnancy (e.g., early embryo death, mid‐pregnancy changes in ovarian function) that may have broader relevance to understanding elasmobranch reproduction. [ABSTRACT FROM AUTHOR]

Ambient temperature modulates reproductive processes, especially in poikilotherms such as teleosts. Consequently, global warming is expected to impact the reproductive function of fish, which has implications for wild population dynamics, fisheries and aquaculture. In this extensive review spanning tropical and cold‐water environments, we examine the impact of higher‐than‐optimal temperatures on teleost reproductive development and physiology across reproductive stages, species, generations and sexes. In doing so, we demonstrate that warmer‐than‐optimal temperatures can affect every stage of reproductive development from puberty through to the act of spawning, and these responses are mediated by age at spawning and are associated with changes in physiology at multiple levels of the brain–pituitary–gonad axis. Response to temperature is often species‐specific and changes with environmental history/transgenerational conditioning, and the amplitude, timing and duration of thermal exposure within a generation. Thermally driven changes to physiology, gamete development and maturation typically culminate in poor sperm and oocyte quality, and/or advancement/delay/inhibition of ovulation/spermiation and spawning. Although the field of teleost reproduction and temperature is advanced in many respects, we identify areas where research is lacking, especially for males and egg quality from "omics" perspectives. Climate‐driven warming will continue to disturb teleost reproductive performance and therefore guide future research, especially in the emerging areas of transgenerational acclimation and epigenetic studies, which will help to understand and project climate change impacts on wild populations and could also have implications for aquaculture. [ABSTRACT FROM AUTHOR]

To investigate the variability in the reproductive tactics of Acıgöl killifish (Aphanius transgrediens), one of the most seriously threatened freshwater teleost species, this study compared its reproductive ecology in two contrasting habitats that differ substantially in terms of stability of environmental parameters, particularly salinity regime (stable vs. unstable). Fish were sampled monthly from October 2013 to September 2014 with the aim of testing whether the reproductive life‐history response of fish to stable and unstable conditions differed. The reproductive effort (gonad weight) of both sexes did not differ significantly between the two habitats, but females in the unstable habitat had significantly lower fecundity and larger eggs. The relationship between fecundity and fish size was stronger in the stable habitat, whereas the relationship was quite variable and uncertain in the unstable habitat. Fish born in the unstable habitat reached their first maturity at a smaller size than those in the stable habitat. The gonado‐somatic index and the duration of hydrated eggs showed that reproduction continued from February to May in both habitats; nonetheless, a second spawning event occurred during July and August in the unstable habitat, which included the reproductive contributions of YOY individuals and older generations. This study's results suggest that A. transgrediens employs varying reproductive strategies against environmental instability in its restricted unique range. This may have further implications for the ways in which habitat‐specific conservation methods are used. [ABSTRACT FROM AUTHOR]

Downstream‐migrating (n = 64) and non‐migrating (n = 21) female Celebes eels Anguilla celebesensis were captured from the Poso Lake–River system on Sulawesi Island, Indonesia, and their reproductive physiological characteristics were examined. A histological observation of the ovaries revealed that most non‐migrating eels were at the perinucleolus (43%) or oil‐droplet (48%) stage, whereas most migrating eels were at the early vitellogenic (36%) or midvitellogenic (61%) stage. Transcript levels of gonadotropin genes (fshb, lhb) in the pituitary gland and concentrations of sex steroids [11‐ketotestosterone (11‐KT), testosterone, 17β‐oestradiol (E2)] in blood plasma of migrating eels were significantly higher than those of non‐migrating eels. The fshb messenger (m)RNA levels were lower in perinucleolus and oil‐droplet stages and then significantly increased in the early vitellogenic stage. The lhb mRNA levels in vitellogenic‐stage eels were significantly higher than those in perinucleolus‐ and oil‐droplet‐stage eels. The 11‐KT levels of eels at the oil‐droplet and vitellogenic stages were significantly higher than those of eels at the perinucleolus stage. The E2 levels at the vitellogenic stage were significantly higher than those at the perinucleolus and oil‐droplet stages. These dynamics of the reproductive hormones represented the physiological background of oogenesis in A. celebesensis that has remarkably well‐developed oocytes just before downstream migration. [ABSTRACT FROM AUTHOR]

Using data from wild Atlantic salmon Salmo salar returning to spawn in seven Scottish rivers, we developed a model of fecundity based on individual body size and key developmental traits. We used a novel approach to model selection which maximises predictive accuracy for application to target river stocks to select the best from a suite of Bayesian hierarchical models. This approach aims to ensure the optimal model within the candidate set includes covariates that best predict out‐of‐sample data to estimate fecundity in areas where no direct observations are available. In addition to body size, the final model included the developmental characteristics of age at smolting and years spent at sea. Using two independent long‐term monitoring datasets, the consequences of ignoring these characteristics was revealed by comparing predictions from the best model with models that omitted them. [ABSTRACT FROM AUTHOR]

We analysed the ovarian dynamics of the anadromous semelparous allis shad Alosa alosa for which our working hypothesis was that mature pre‐spawning females would have very low or even exhausted primary growth (PG) oocyte reserves; semelparity has been linked with the depletion of the pool of PG oocytes. To test this hypothesis, the PG oocytes were enumerated, their recruitment pattern to the secondary growth (SG) phase was analysed and their potential replenishment from the pool of oogonia was examined in females caught very close to the Mondego River mouth, in central Portugal and along the river. The development of the SG oocytes was also analysed, the fecundity (batch, total and annual) values were estimated and the intensity of atresia was quantified. Ovarian samples and histological sections were investigated in parallel. A dynamic recruitment pattern of PG oocytes to the SG phase was revealed, where all PG oocytes were recruited and were not replenished by oogonia. Annual fecundity was subject to down‐regulation due to atresia prior to spawning and its size was multiple times higher than the size of batch fecundity. Lack of population synchronicity in ovarian development and spawning migration was also observed. This multifaceted analysis of the ovarian dynamics of this species will contribute to management efforts for this critically endangered and economically important fish throughout its geographical distribution. The results reported in this study will also assist in unravelling the complexity of the early processes of oogenesis in fish. [ABSTRACT FROM AUTHOR]

The California butterfly ray Gymnura marmorata is frequently caught by artisanal fisheries in north‐western Mexico (Baja California Sur; BCS). The aim of this study was to estimate reproductive characteristics and describe the micro and macroscopic reproductive structures of female and male G. marmorata. Sampling was carried out at two fisheries landing sites located on the west coast BCS, from 2008 to 2012. The largest disc width (WD) ever recorded for this species was 131.0 cm and females were larger than males. The male sample was composed exclusively of adult specimens, with a median size at 50% maturity (WD50) estimated at 44.9 cm WD. For females, size at onset of maturity was estimated at 63.0 cm WD; WD50, at 64.7 cm WD; and size at pregnancy at 80.1 cm WD. Gonadal asymmetry was observed for the first time in this species. Indeed, in males only the left testis was functional (testicular asymmetry), while in females, only the left ovary was functional (ovarian asymmetry). [ABSTRACT FROM AUTHOR]

A combination of traditional and emerging methodologies was used to assess the trade‐offs between several life‐history traits (linked to reproduction and condition) and parasitism in a commercially‐exploited cold‐water species, blue whiting Micromesistius poutassou, in the Mediterranean Sea. The use of histological and gravimetric methods revealed conflicting evidence as to the fecundity type (indeterminate or determinate) of this species. Moreover, there seem to be condition‐mediated compensations between egg quality and egg quantity. The effects of parasitism on reproduction and condition are species‐specific and occur mainly at high intensities of infection; they include a lower batch fecundity (affecting reproductive potential), a higher hepatosomatic index and a higher spleen‐somatic index. Considering the fact that larger fish spawn more eggs and that the minimum landing size is lower than the size at maturity, these results may have implications for the future management of M. poutassou stocks in the Mediterranean Sea. Local environmental conditions may account for geographical differences regarding infection in M. poutassou. Altogether, the results support the idea that the complex trade‐offs between parasitism, reproduction and condition need to be considered in order to understand the status of cold‐water species such as M. poutassou. [ABSTRACT FROM AUTHOR]

This study examined the usefulness of portable ultrasonography in accurately predicting pregnancy and fecundity in the bonnethead shark Sphyrna tiburo by comparing ultrasound‐obtained data with those obtained from animal dissection, the gold standard for elasmobranch reproduction studies. Mature female S. tiburo (n = 66) were collected throughout the period of reproduction and examined via portable ultrasonography using two different ultrasound transducers (8–5 MHz linear array transducer and a 5.0–2.5 MHz curvilinear array transducer) to determine pregnancy status and fecundity. Ultrasound‐derived data were compared with validated assessments of pregnancy and litter size obtained using animal dissection to determine the level of agreement between the two approaches. Overall, there was strong agreement (90.9%) between pregnancy determinations obtained using ultrasonography and dissection. However, the effectiveness of portable ultrasonography in accurately determining specific stages of maturity and pregnancy differed slightly between transducer types (linear = 61.3%; curvilinear = 88.9%). Measurements of fecundity also agreed well between ultrasonography and dissection and there were no significant differences between mean fecundity estimates obtained using the two methods. In general, portable ultrasonography was found to be a good alternative to lethal sampling and animal dissection in obtaining reproductive data critical for the management and conservation of elasmobranchs. Special attention should be given to factors that can influence the reliability of ultrasound‐derived data such as transducer type, embryo size and sound wave interference due to gut contents. [ABSTRACT FROM AUTHOR]

Age, growth and reproductive characteristics of six westslope cutthroat trout Oncorhynchus clarkii lewisi populations were studied in the south‐western Rocky Mountains in Alberta, Canada. Sagittal otoliths were collected from 605 fish ranging in size from 36 to 250 mm (fork length). The maximum detected age (13 years for females and 12 for males) was higher than has been reported previously in published literature; but no significant differences in age distributions between males and females were found. Length growth rates, estimated using the von Bertalanffy growth function, showed that males and females had similar growth rates. Sex ratios varied between 0.3 to 2.0 females per male. Age and size at 50% maturity were greater for females than males (4.9 years and 139 mm v. 3.7 years and 125 mm). Mature females were yearly spawners with highly variable fecundities (mean ± S.D. = 223 ± 94) and their ovaries contained both developed and undeveloped eggs. Across all populations, mean instantaneous mortality rate (Z) was estimated as 0.555, annual survival rates for 0–1 year‐old fish were 3.2 and 57.4% for older fish. An altitudinal distribution gradient was observed, with older fish occupying upper stream reaches. This study provides a comprehensive evaluation of biological characteristics and structure of O. c. lewisi populations inhabiting small, mountain streams and should provide useful basic information for management policies of this threatened species in eastern drainage of the Canadian Rocky Mountains. [ABSTRACT FROM AUTHOR]

Length and mass data for 1260 (536 females, 683 males, 41 sex unknown) striped marlin Kajikia audax were collected at the fish markets of Tungkang, Singkang and Nanfangao from July 2004 to September 2010. Of these samples, 534 gonads (236 females and 298 males) ranging from 95 to 206 cm in eye-to-fork length ( LEF) and 8 to 88 kg in round mass ( MR), were collected. Chi-square tests indicated sex ratios were homogeneous among months in 2004 and 2006-2008, but not in 2005, 2009 and 2010; and there were significant differences in sex ratio by size. The overall sex ratio ( RS) differed significantly from the expected 0·5. Kajikia audax are sexually dimorphic and the proportions of females increased with size between 140 and 210 cm LEF. Reproductive activity was assessed using a gonado-somatic index ( IG), external appearance of the gonads and histological examination and results indicated that the spawning season occurred from April to August with a peak in June to July. Based on histological observations and the distribution of oocyte diameters, K. audax are multiple spawners and their oocytes develop asynchronously. The estimated length-at-50% maturity ( LEF50) was c. 181 cm ( c. 4·8 years of age) for females. The proportion of reproductively active females in the spawning season with ovaries containing postovulatory follicles (0·27) indicated that they spawned every 3·7 days on average. The hydrated oocyte method estimated mean ± S.D. batch fecundity ( FB) to be 4·4 ± 2·02 million eggs; average relative fecundity was 53·6 ± 13·9 oocytes g−1 MR; and the average annual fecundity was 181·3 ± 48·3 million eggs. The parameters estimated in this study are key information for stock assessments of K. audax in the north-western and central Pacific and will contribute to the conservation, management and sustainable yield of this species. [ABSTRACT FROM AUTHOR]

Spawning performance of pinfish Lagodon rhomboides without use of hormonal aids was monitored over an extended season. Nearly three million eggs were obtained from 75 spawns collected over a 90-day consecutive period from a single population of four brood fish (1M:1F). A mean ± s.d. batch fecundity of 30·27 ± 22·64 eggs g−1 female was estimated with 98·0 ± 0·06% of the batch composed of floating eggs which were 1·04 ± 0·04 mm in diameter and 85·71 ± 27·59% fertile. Floating eggs successfully hatched 54·65 ± 29·13% of the time which yielded larvae that were 2·59 ± 0·24 mm in length. Fatty acids within floating eggs were largely represented by polyunsaturated fatty acids (45·30 ± 2·14% of total fatty acids) of which linoleic acid [(c18:2 n-6cis) 3·49 ± 1·69% trifluoroacetic acid (TFA)] and docosahexaenoic acid (DHA) [(c22:6 n-3) 28·47 ± 1·48% TFA] represented the majority of fatty acids for n-6 and n-3 polyunsaturated fatty acids, respectively. The strongest correlations between fatty acids and hatching success and larval survival to first feeding were observed for the DHA:EPA (eicosapentaenoic acid; c20:5 n-3) ratio and total n-6 polyunsaturated fatty-acids levels, respectively. These data demonstrate potential for producers to rely on natural spawns for extensive egg production and provide a baseline for future development of natural spawning protocols of captive L. rhomboides. [ABSTRACT FROM AUTHOR]

This study presents information on the reproductive biology of Psammobatis rutrum based on 55 males and 53 females obtained as by-catch from bottom trawlers off southern Brazil during July 2013 and September 2014 and includes a detailed description of the egg capsule. Total lengths ( LT) ranged from 22·3 to 31·6 cm and most of the sample comprised larger individuals, although there were no sexual differences in length-frequency distributions. Significant sexual differences were found for total length-disc width, LT-body mass and LT-eviscerated body mass relationships, with females being heavier and larger. Males started to mature at 25·5 cm LT and females, at 25·9 cm LT, while LT at maturity was calculated in 26·67 and 26·81 cm, respectively. Attaining larger sizes and mass may represent a reproductive investment for females, as observed in other rajoid species. Egg bearing females were first observed over 27·1 cm LT and ovarian fecundity was 1-12 vitellogenic follicles. The egg capsules were 2·22-2·62 cm length and had attaching fibrils on both lateral sides. Microscopically, the ventral face of the egg capsule was rougher than the dorsal face. [ABSTRACT FROM AUTHOR]

Macrhybopsis reproduction and propagule traits were studied in the laboratory using two temperature regimes and three hormone treatments to determine which methods produced the most spawns. Only sicklefin chub Macrhybopsis meeki spawned successfully although sturgeon chub Macrhybopsis gelida released unfertilized eggs. All temperature and hormone treatments produced M. meeki spawns, but two treatments had similar success rates at 44 and 43%, consisting of a constant daily temperature with no hormone added, or daily temperature fluctuations with hormone added to the water. Spawns consisted of multiple successful demersal circular swimming spawning embraces interspersed with circular swims without embraces. The most spawns observed for one female was four and on average, 327 eggs were collected after each spawn. The water-hardened eggs were semi-buoyant and non-adhesive, the first confirmation of this type of reproductive guild in the Missouri River Macrhybopsis sp. From spawn, larvae swam vertically until 123 accumulated degree days ( ° D) and 167° D for consumption of first food. Using average water speed and laboratory development time, the predicted drift distance for eggs and larvae could be 468-592 km in the lower Missouri River. Results from this study determined the reproductive biology and early life history of Macrhybopsis spp. and provided insight into their population dynamics in the Missouri River. [ABSTRACT FROM AUTHOR]

This study describes the spawning of the fatheads Psychrolutes marmoratus and Cottunculus granulosus, two psychrolutid species that inhabit the shelf edge and continental slope of the south-west Atlantic. Females lay large eggs of c. 2·5 mm ( P. marmoratus) and 4·5-5·0 mm ( C. granulosus); fecundity is from the hundreds ( C. granulosus) to a few thousand eggs ( P. marmoratus). Egg maturation is synchronous in P. marmoratus with an autumn-winter peak of spawning and group-synchronous in C. granulosus, which reproduces all year round. In the fishery, females predominate among adult fish in both species, possibly indicating male nest guarding on hard grounds inaccessible to fishing vessels. The reproductive strategy of representatives of the Psychrolutidae is similar to that of other sculpins of the superfamily Cottoidea. [ABSTRACT FROM AUTHOR]

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre-spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October-early November, at a leading cohort size ( CL) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre-spawning, but atretic re-absorption of remnant oocytes containing yolk granules was found in all females immediately post-spawning. As expected, concentrations of sex steroids, oestradiol-17β (females), testosterone (both sexes) and 11-ketotestosterone (both sexes), increased pre-spawning before dropping post-spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post-ovulatory follicles were visible in histological sections from female gonads 9-11 months post-spawning, but then disappeared. Spawning commenced around a CL of c. 750 µm (700-800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, LT = 60 cm). Spawning lasted from 13 February to 29 March. [ABSTRACT FROM AUTHOR]

Theory and empirical estimates agree that the ratio of effective size ( Ne) to census size ( N) falls roughly in the range 0·1-0·5 for most populations. In a number of marine species, however, genetic estimates of contemporary Ne/ N are as much as 5-6 orders of magnitude lower. Although some mechanisms that could produce such tiny Ne/ N ratios have been proposed, the subject remains controversial. This issue is important to resolve: if Ne/ N can be 10−3 or smaller, marine fish populations that are quite large could be at genetic risk. Based on a recently-improved understanding of factors that influence Ne and Ne/ N in species with overlapping generations, this paper evaluates conditions necessary to produce tiny Ne/ N ratios in actual populations. These analyses show that although increased longevity, fecundity and variance in reproductive success that increase with age, and increased egg quality with age [the big old fat fecund female fish ( BOFFFF) hypothesis] all reduce Ne/ N, extreme scenarios are required to reduce Ne/ N below about 0·01. Therefore, tiny Ne/ N ratios require some version of Hedgecock's 'sweepstakes' hypothesis, whereby only a few families reproduce successfully. Simulations using common genetically-based estimators show that, when true Ne is very large (≥106), a substantial fraction of point estimates of Ne/ N can be 10−3 or smaller. These results mean that tiny, genetically-based point estimates of Ne/ N in large marine populations are expected to be quite common, even when the true Ne/ N ratio is 'normal' (∼0·1 or higher). Very large samples of individuals can reduce, but not eliminate, this problem. The simulation results also emphasize the importance of considering deviations from model assumptions ( e.g. non-random sampling; weak selection or migration) that may be relatively small (and hence can generally be ignored when the signal is strong) but can lead to substantial biases when the drift signal is weak, as is likely for large marine populations. Empirical studies of this topic need to be able to distinguish between episodes of sweepstakes reproductive success that are ephemeral and lead to chaotic genetic patchiness, and those that are consistent enough across space and time to produce persistent evolutionary consequences. [ABSTRACT FROM AUTHOR]

This study describes the reproductive strategy of the stream-dwelling catfish Hatcheria macraei in the Pichileufu River, Argentina. Gonad maturity phases, classified on the basis of histological analysis, stages of gamete development and the frequency distribution of oocyte size, were correlated with macroscopic features of the gonads. Hatcheria macraei has a cystovarian ovary, asynchronous oocyte development and lobular testes. Five oocyte and four spermatogenic stages were identified and related to macroscopic gonad characteristics, making it possible to divide gonad development into five phases for females and males. Mature oocyte diameter ranged from 922 to 1935 µm. Absolute fecundity in mature females varied from 115 to 480 oocytes. Hatcheria macraei has multiple spawning during a protracted reproductive season that extends from December to April. This, together with its small size, is characteristic of an opportunistic reproductive strategy, commonly found in species that inhabit adverse and unpredictable environments, such as the low-order rivers of Patagonia. [ABSTRACT FROM AUTHOR]

The reproductive biology of Urotrygon microphthalmum was studied based on specimens caught as by-catch in shrimp ( Litopenaeus schmitti, Xiphopenaeus kroyeri, Farfantepenaeus subtilis and Farfantepenaeus brasiliensis) fishing operations between March 2010 and March 2012 on the coast of Pernambuco, Brazil. Females reached a larger total length ( LT) and total body mass ( MT) (298 mm and 148 g) than males (250 mm and 90 g). Length at maturity was estimated to be 188 and 199 mm LT for males and females. Uterine fecundity ranged from one to four embryos (mean ± s.d.: 1·85 ± 0·45). Size at birth was estimated to be 105 mm LT. Gestation lasted between 4 and 5 months. The reproductive cycle of U. microphthalmum is hypothesized to be asynchronous and biannual. [ABSTRACT FROM AUTHOR]

The reproductive biology of two inseminating Glandulocaudini species, Mimagoniates microlepis and Mimagoniates rheocharis, was investigated and compared with reproductive patterns described for other inseminating and non-inseminating characids, hypothesizing the evolutionary history of these reproductive traits. The long reproductive period, with higher activity in colder months, distinguishes the reproductive strategy of these species when compared with most characiforms. The M. rheocharis population was structured in two groups of males throughout the year, mature males with high gonado-somatic index ( IG = 2·0 and 4·4) and immature and maturing males with low IG values (0·0 and 1·2). Mimagoniates rheocharis and M. microlepis showed the lowest absolute mean fecundities known for characids, indicating that inseminating species allocate less energy to oocyte production and reinforcing the hypothesis that insemination has an adaptive advantage, which provides a higher chance of fertilization. [ABSTRACT FROM AUTHOR]

The reproductive biology and other life-history parameters were investigated for Mustelus asterias in British waters, with specimens caught from both commercial fisheries and research-vessel surveys. In total, 504 specimens [238 males, 24-99 cm total length ( LT) and 266 females, 28-124 cm LT] were examined, with further information collected from 238 uterine pups. The lengths at 50% maturity were estimated as 70·4 and 81·9 cm LT for males and females, respectively. Ovarian fecundity ranged from one to 28, and uterine fecundity from four to 20. The number, mass and LT of pups were positively correlated with maternal LT. Full-term pups ranged from 205 to 329 mm LT, and the smallest free-living fish caught was 24 cm LT. Parturition occurred in February in the western English Channel and during June to July in the eastern English Channel and southern North Sea, indicating either protracted spawning or asynchronous parturition for the stock as a whole. The reproductive cycle is thought to extend beyond 1 year. Developmental abnormalities observed included atresia in oocytes, uterine eggs that failed to develop, a partly developed pup and an abnormal male with a single aberrant clasper. Data relating to conversion factors, oocyte numbers and diameter and gonado-somatic and hepato-somatic indices are presented, and the seasonality of the reproductive cycle is discussed. [ABSTRACT FROM AUTHOR]

This study investigated demographic structure and reproductive characteristics of the Atlantic mackerel Scomber scombrus, in relation to landing trends in the northern-central Adriatic Sea. Results highlighted the occurrence of only small-sized and young-age individuals, and a marked decline from the 1990s to the present in maximum age (from 8 to 3 years) and total length ( LT; from 420 to 360 mm). Fecundity ranged between 40 000 and 190 000 eggs, and was related to female LT. High levels of atresia implied lower values of actual fecundity. Sexual maturity was attained by 72·8% of individuals in their first year of life at 200 mm. The reduction in maximum LT resulted in a marked decline in the population egg production, while the reduction in maximum age implied that females participated in fewer spawning events. [ABSTRACT FROM AUTHOR]