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.

Impacts of climate change on ocean productivity sustaining world fisheries are predominantly negative but vary greatly among regions. We assessed how 39 fisheries resources-ranging from data-poor to data-rich stocks-in the North East Atlantic are most likely affected under the intermediate climate emission scenario RCP4.5 towards 2050. This region is one of the most productive waters in the world but subjected to pronounced climate change, especially in the northernmost part. In this climate impact assessment, we applied a hybrid solution combining expert opinions (scorings)-supported by an extensive literature review-with mechanistic approaches, considering stocks in three different large marine ecosystems, the North, Norwegian and Barents Seas. This approach enabled calculation of the directional effect as a function of climate exposure and sensitivity attributes (life-history schedules), focusing on local stocks (conspecifics) across latitudes rather than the species in general. The resulting synopsis (50-82°N) contributes substantially to global assessments of major fisheries (FAO, The State of World Fisheries and Aquaculture, 2020), complementing related studies off northeast United States (35-45°N) (Hare et al.,

BackgroundFish correspond to the most diversified phylum among vertebrates with a large variety of species. Even if general features are distinguishable during the embryogenesis, several differences in term of timing, organ implementation or step progression always occur between species. Moreover, the developmental timing of wild non-model fish often presents variability within a species. In that context, it is necessary to define a model of developmental table flexible enough to describe fish development by integrating this variability and allow intra- and inter-specific comparisons. The elaboration of a model passes by the definition of new stages that could be easily observable on individuals. The present study aims at proposing such a model and describing accurately the Eurasian perch (Perca fluviatilis) embryogenesis using microscopic techniques among which time lapse video and histological studies. The Eurasian perch belongs to the Percidae family that includes 235 species classified in 11 genera. It is a member of the Perca gender and inhabits the Northern part of Europe and Asia.ResultsAt 13 °C, P. fluviatilis development elapses for 15 days from the fertilization to the first oral feeding. The staging division first took into account the cellular status to define periods, then the acquisition of new abilities by the embryo to further define stages. It allowed distinguishing two main stages during the cell cleavage period depending on the synchronization of the cell divisions, two stages during the gastrulation period depending on the cell speed migration and five stages during the organogenesis according to the acquisition of key abilities as proposed in the saltatory theory. During each stage, organs implementation was carefully followed with a particular attention for the visual and digestive systems. In addition, our study shows that embryos hatch at various developmental stages while they all begin to feed at a fixed date, 15 days after the fertilization whatever the spawn and the hatching date. These data give arguments to propose the first oral feeding as the best definition of the embryonic-to-larval transition.ConclusionsThe present model of developmental table combines flexibility and accuracy allowing detailed description of non-model fish species and intra- and inter-specific comparisons.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-015-0033-3) contains supplementary material, which is available to authorized users.

Improving reproductive protocols is one crucial step towards aquaculture expansion of pikeperch (Sander lucioperca), which is still characterised by variable and/or low spawning effectiveness. One of the main challenges is to synchronise ovulation at a precisely planned time with a consistently satisfactory reproductive outcome. To this end, the present study examined the effect of different spawning agents (human chorionic gonadotropin [hCG] and salmon gonadotropin-releasing hormone analogue [sGnRHa]) with different doses and application modes (including double injection). The study covered three consecutive spawning seasons, which corresponded to three distinct experiments, where domesticated pikeperch broodstock, commercially grown in a recirculating aquaculture system, was used. In the first year of the study, the effect of different doses of sGnRHa (10, 25 and 50 μg kg -1 ) and hCG (250, 500 and 1000 IU kg -1 ) on the reproductive performance of the domesticated broodstock was evaluated. The results were also compared with literature data for wild fish. During the second and third years, typical indicators of spawning performance (ovulation rate, latency time and egg quality) were followed when a double sGnRHa injection was compared to a single 50 µg kg -1 or 500 IU kg -1 injection of sGnRHa or hCG, respectively; the best results were 2 obtained in the first and second experiments. The results of the present study clearly indicate that various hormonal treatments effectively induced domesticated pikeperch ovulation, although highly variable egg quality was observed throughout the three spawning seasons (maximum hatching rates were 60.6 ± 11.5, 37.7 ± 28.9 and 49.1 ± 24.7% in the first, second and third years of the study, respectively). However, additional analysis of the data from the entire study revealed for the first time that a significant proportion of the lower-quality eggs came from fish that responded 'early' to hormonal treatment (<120 h after injection) regardless of the hormone used. This group represented approximately 40% of the population each year.Further, most of the fish that responded to hormone treatment early exhibited this trait during all three consecutive spawning seasons. This finding indicates that early hormone response is a potential selection trait. The present study showed that controlled domesticated pikeperch broodstock reproduction may involve application of either hCG or sGnRHa, with no clear difference in their effectiveness, although the recommended doses are 500 IU kg -1 and 50 µg kg -1 , respectively.

The collection and presentation of accurate reproductive data from wild fish has historically been somewhat problematic, especially for serially spawning species. Therefore, the aim of the current study was to develop a novel method of assessing female spawning status that is robust to variation in oocyte dynamics between specimens. Atlantic cod (Barents Sea stock) were used to develop the new 'ultrametric' method, that is based on the progressive depletion of the vitellogenic oocyte pool relative to the rather constant previtellogenic oocyte (PVO) pool. Fish were subsequently partitioned into one of four categories that accurately reflected changes in their oocyte size frequency distribution characteristics and gonadosomatic index throughout spawning. the ultrametric method overcomes difficulties associated with presence of bimodal oocyte distributions, oocyte tails, lack of clear hiatus region, and presence of free ova, and can be implemented at a single sampling point. Much of the workflow is fully automated, and the technique may circumvent the need for histological analysis depending on the desired outcome. The ultrametric method differs from the traditional autodiametric method in that PVOs can be separated by ultrasonication and then enumerated, and ovarian homogeneity is not a mandatory requirement per se. The method is designed for determinate spawners but might be extended to include indeterminate spawners.

The domestication process is accompanied with adaptation of the animals to captive conditions. It induces changes at different levels thereby affecting a variety of biological functions. While there is abundant literature on the domestication effects on growth and stress response in teleosts, the effects on reproduction have received limited attention. In this work, we investigated the domestication effect on reproductive ability of Eurasian perch (Perca fluviatilis L.), a promising candidate for the development of European aquaculture and whose reproductive physiological processes through the domestication history has not been questioned yet.To address this question, two populations of F1 and "domesticated" females were submitted to a photothermal program allowing the control of gonadogenesis advancement. Gonadosomatic index, 17 β-estradiol levels and oocyte diameter were significantly higher in domesticated population than in F1 one. In contrast, testosterone, 11-ketotestosterone, and vitellogenin levels were found to be higher in F1 females than in their domesticated counterparts. Lower reproductive performance were observed in the domesticated population compared to the F1 one in terms of survival rate, hatching rate, percentage of eyed stage larvae and percentage of malformations. In conclusion, this study shows that, in this example of domestication process, despite a positive effect on the precocious gonadogenesis advancement and vitellogenesis progress this domestication route negatively affected the reproductive performance.

During the teleost ontogenesis, biotic and abiotic factors influence organs deformations. Despite of an important literature, the potential causes of deformities in fish are still poorly understood. Cultured fish in artificial conditions exhibit higher incidence of developmental impairments compared to wild ones. This study aims at describing exhaustively the deformity categories of newly hatched embryos of Eurasian perch and investigating at once all biotic and abiotic factors of two extremely different rearing systems [recirculating aquaculture system (RAS) vs. ponds] on their occurrence. The description and clustering of deformities according to the organs involved allowed not only to show that skeletal, cardiac and yolk anomalies are the most common ones, but also to highlight new functions undergoing developmental failure (locomotive, digestive and excretory systems). In total, 10 categories of abnormalities have been described. In addition, our data show a relationship between the cardiac and yolk deformities suggesting common causes. In a second part, we compared the incidence of deformities in the progeny of two distinct populations of fish, reared under extremely various conditions (RAS vs. pond). The total deformity rates did not differ between the groups but the nature of deformities was surprisingly different as the RAS reared fish (RRF) originating from fisheries presented a higher variety of deformity categories than the fish originating from Lorraine ponds (LPRF). Indeed, cardiac, yolk and skeletal axis deformities were more frequent in RRF embryos, whereas mouth abnormalities were preferentially represented in LPRF embryos. These findings may help understanding the potential causes of these developmental impairments in cultured animals and may lead to the improvement of husbandry conditions.

Domestication is an evolutionary process during which we expect populations to progressively adapt to an environment controlled by humans. It is accompanied by genetic and presumably epigenetic changes potentially leading to modifications in the transcriptomic profile in various tissues. Reproduction is a key function often affected by this process in numerous species, regardless of the mechanism. The maternal mRNA in fish eggs is crucial for the proper embryogenesis. Our working hypothesis is that modifications of maternal mRNAs may reflect potential genetic and/or epigenetic modifications occurring during domestication and could have consequences during embryogenesis. Consequently, we investigated the trancriptomic profile of unfertilized eggs from two populations of Eurasian perch. These two populations differed by their domestication histories (F1 vs. F7+–at least seven generations of reproduction in captivity) and were genetically differentiated (FST = 0.1055, p<0.05). A broad follow up of the oogenesis progression failed to show significant differences during oogenesis between populations. However, the F1 population spawned earlier with embryos presenting an overall higher survivorship than those from the F7+ population. The transcriptomic profile of unfertilized eggs showed 358 differentially expressed genes between populations. In conclusion, our data suggests that the domestication process may influence the regulation of the maternal transcripts in fish eggs, which could in turn explain differences of developmental success.