Sylvie Bolla

Combined effects of temperature and salinity on development and survival of Atlantic halibut larvae

The effects of different combinations of temperature and salinity on development and survival of Atlantic halibut, Hippoglossus hippoglossus (L.), larvae were studied in two experiments. In the period from 57 to 120 d° post hatching, approximately 38% of the larvae died: in both experiments, mortality was significantly related to temperature, but there was no relationship to salinity.Cumulative, chronic mortality during the yolk-sac stage (until 210 d°) was related to salinity. High mortality was observed in both experiments when high salinity (>34%) was combined with incubation at either high (9 °C) or low (3 °C) temperature. The development of head lesions was significantly related to temperature, and for larvae kept at high salinity, increased mortality may have been a result of salinity stress in the injured larvae.Abnormal development of the caudal notochord, sometimes resulting in a 90-degree bend of the tail, occurred during incubation of early yolk-sac larvae in high-salinity water. The occurrence of larvae with locked jaws, and larvae with oedema in the yolk-sac sinus and pericardium, was significantly related to temperature.

Maternal gene expression in Atlantic halibut (Hippoglossus hippoglossus L.) and its relation to egg quality

BackgroundThe commercial production of Atlantic halibut (Hippoglossus hippoglossus L.) suffers from a major bottleneck due to the low success of producing juveniles for on-growing. Atlantic halibut females are routinely hand-stripped and incorrect timing of stripping can result in low quality eggs due to post-ovulatory aging. Post-ovulatory aging leads to compositional changes in eggs that include maternally provided proteins and RNAs. There have been few studies of the maternally provided mRNA transcripts that control early development in commercially important fish species. The present study aimed to study maternal gene expression in Atlantic halibut and its relation to egg quality parameters including blastomere symmetry and hatching success.ResultsA maternal EST library containing 2341 sequences was constructed by suppressive subtractive hybridisation. Thirty genes were selected for expression studies; 23 novel genes and 7 genes with documented roles in early development. The expressions of twenty-one selected genes were measured by qPCR from fertilization to the 10-somite stage. Three genes were identified as strictly maternal genes that were expressed until the start of gastrulation; askopos (kop), si:dkey-30j22.9 (Tudor family member), and Tudor 5 protein (Tdrd5). The expressions of 18 genes at the 8-cell stage were correlated with egg quality parameters. The majority of genes showed either no or very minor correlations with egg quality parameter. However, two genes correlated positively with hatching success (r> 0.50, HHC00353: r = 0.58, p < 0.01; HHC01517: r = 0.56, p < 0.01) and one gene (HHC00255) was negatively correlated with the percentage of normal blastomeres (r = -0.62, p < 0.05).ConclusionsDuring this study we have related maternal levels of gene expression to hatching success in fish. Poor hatching success was not correlated with a general decrease in transcript abundance but with low transcript levels of some specific genes. Thus, the molecular mechanisms leading to low Atlantic halibut egg quality cannot be entirely explained by post-ovulatory aging.

Induction of meiotic gynogenesis in Atlantic cod (Gadus morhua L.) through pressure shock

The Atlantic cod, Gadus morhua, is one of the most important species for commercial fisheries and a promising candidate for aquaculture. Precocious sexual maturation of males is one of the major issues compromising large scale production. The potential approaches to this problem include production of all female populations. Consequently, the objective of this study was to develop an effective protocol to induce meiotic gynogenesis in the Atlantic cod by using hydrostatic pressure shock. Our first experiment tested the relevance of gamete quality on achievement of chromosome manipulation and identified the best time interval between fertilization and pressure shock. Our second experiment was designed to determine the optimal pressure value and duration of the pressure shock. Eight combinations of pressure values and durations were tested. Among them, the 34.47 MPa/6 min combination gave the best survival rate (23.6 ± 3.9%), the highest percentage of normal larvae (15.7 ± 3.6%), and the highest percentage of meiotic diploids (88.89%). In both experiments, haploid controls served as an indirect reference for paternal DNA inactivation. Chromosome counting confirmed the restoration of diploidy in gynogenetic fish. The present study optimizes a procedure for the induction of meiotic gynogenesis in the Atlantic cod, thus laying the basis for further applications towards producing monosex and defining the sex determination system.