Ontogenic effects of early feeding of sea bass (Dicentrarchus labrax) larvae with a range of dietary n-3 HUFA levels on the functioning of PUFA desaturation pathways

Four replicated groups of sea bass (Dicentrarchus labrax) larvae were fed diets containing an extra-high level of highly unsaturated fatty acids (HUFA) (XH; 3·7% EPA + DHA), a high level of HUFA (HH; 1·7 %), a low level of HUFA (LH; 0·7%) or an extra-low level of HUFA (XLH; 0·5%) from day 6 to day 45 (experiment 1; XH1, HH1, LH1, XLH1). After a subsequent 1-month period feeding a commercial diet (2·7% EPA + DHA), the capacity of the four initial groups to adapt to an n-3 HUFA-restricted diet (0·3% EPA + DHA; R-groups: XH2R, HH2R, LH2R, XLH2R) was tested for 35 d. Larval dietary treatments had no effect on larval and juvenile survival rates. The wet weight of day 45 larvae was higher in XH1 and HH1 (P < 0·001), but the R-juvenile mass gains were similar in all treatments. D-6-desaturase (D6D) mRNA level was higher in LH1 and XLH1 at day 45 (

Smaller herring larval size-at-stage in response to environmental changes is associated with ontogenic processes and stress response

Global change puts coastal systems under pressure, affecting the ecology and physiology of marine organisms. In particular, fish larvae are sensitive to environmental conditions, and their fitness is an important determinant of fish stock recruitment and fluctuations. To assess the combined effects of warming, acidification and change in food quality, herring larvae were reared in a control scenario (11°C*pH 8.0) and a scenario predicted for 2100 (14°C*pH 7.6) crossed with two feeding treatments (enriched in phosphorus and docosahexaenoic acid or not). The experiment lasted from hatching to the beginning of the post-flexion stage (i.e. all fins present) corresponding to 47 days post-hatch (dph) at 14°C and 60 dph at 11°C. Length and stage development were monitored throughout the experiment and the expression of genes involved in growth, metabolic pathways and stress responses were analysed for stage 3 larvae (flexion of the notochord). Although the growth rate was unaffected by acidification and temperature changes, the development was accelerated in the 2100 scenario, where larvae reached the last developmental stage at a smaller size (−8%). We observed no mortality related to treatments and no effect of food quality on the development of herring larvae. However, gene expression analyses revealed that heat shock transcripts expression was higher in the warmer and more acidic treatment. Our findings suggest that the predicted warming and acidification environment are stressful for herring larvae, inducing a decrease in size-at-stage at a precise period of ontogeny. This could either negatively affect survival and recruitment via the extension of the predation window or positively increase the survival by reducing the larval stage duration

The effects of dietary marine protein hydrolysates on the development of sea bass larvae, Dicentrarchus labrax, and associated microbiota

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