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.

Background In the animal kingdom, mollusca is an important phylum of the Lophotrochozoa. However, few studies have investigated the molecular cascade of sex determination/early gonadal differentiation within this phylum. The oyster Crassostrea gigas is a sequential irregular hermaphrodite mollusc of economic, physiological and phylogenetic importance. Although some studies identified genes of its sex-determining/−differentiating pathway, this particular topic remains to be further deepened, in particular with regard to the expression patterns. Indeed, these patterns need to cover the entire period of sex lability and have to be associated to future sex phenotypes, usually impossible to establish in this sequential hermaphrodite. This is why we performed a gonadal RNA-Seq analysis of diploid male and female oysters that have not changed sex for 4 years, sampled during the entire time-window of sex determination/early sex differentiation (stages 0 and 3 of the gametogenetic cycle). This individual long-term monitoring gave us the opportunity to explain the molecular expression patterns in the light of the most statistically likely future sex of each oyster. Results The differential gene expression analysis of gonadal transcriptomes revealed that 9723 genes were differentially expressed between gametogenetic stages, and 141 between sexes (98 and 43 genes highly expressed in females and males, respectively). Eighty-four genes were both stage- and sex-specific, 57 of them being highly expressed at the time of sex determination/early sex differentiation. These 4 novel genes including Trophoblast glycoprotein-like, Protein PML-like, Protein singed-like and PREDICTED: paramyosin, while being supported by RT-qPCR, displayed sexually dimorphic gene expression patterns. Conclusions This gonadal transcriptome analysis, the first one associated with sex phenotypes in C. gigas, revealed 57 genes highly expressed in stage 0 or 3 of gametogenesis and which could be linked to the future sex of the individuals. While further study will be needed to suggest a role for these factors, some could certainly be original potential actors involved in sex determination/early sex differentiation, like paramyosin and could be used to predict the future sex of oysters.