Following the disappearance of the St. Lawrence population of striped bass Morone saxatilis, the Government of Quebec has undertaken in 2002 a major program to reintroduce the species in former habitats. However, to meet the challenges posed by the restocking efforts, a better knowledge of the biology of this species is required, particularly their physiology related to development. We focussed on the effects of diet content in polyunsaturated fatty acids (PUFA) considering their fundamental role in early development. PUFA are almost exclusively synthesized by plants, and although animals can move from one form of PUFA to another using elongation and desaturation processes, very few species can synthesize PUFA de novo. PUFAs play an important role in regulating the properties of the cell membrane, serve as precursors for important animal hormones and are therefore essential to maintain animals healthy.
We tested the hypothesis that variable salinity and food source (estuarine vs marine sources) would markedly impact the physiology of striped bass juveniles. Juveniles were raised in winter conditions at two salinities (0 and 14) and fed with a reference diet used as a proxy of an estuarine trophic network (0.73% n-3 PUFA), and a higher n-3 PUFA diet (1.65%) used as a proxy of a marine trophic network. Preliminary results showed that salinity effects were less pronounced compared to those of dietary regimes on total liver and muscle neutral fatty acid (FA) profiles, white muscle polar FA were slightly affected. Also, nutritional essential FA (EPA and DHA respectively) needs were higher when fish were growth in fresh water (FW). These results suggest that FW represented a stressful condition for juvenile striped bass, and this was corroborated by the higher hematocrit value and the lower survival observed in FW. Further work is in progress to investigate how the fatty acid regulation is achieved through the study of the expression of some genes used as a proxy of the fatty acid synthesis (fatty acid synthetase complex fas and delta 6-desaturase gene fads2), lipid homeostatic processes (peroxisome proliferative activated receptors ppars), elongases and desaturases activity (sterol regulatory element binding protein-1 srebp-1), and the stress response (molecular chaperones heat shock proteins hsp70, hsp90 and hsf1 interacting with members of several signal transduction pathways).