Dietary Lecithin Source Affects Growth Potential and Gene Expression in Sparus aurata Larvae

13 páginas, 5 figuras, 7 páginas.Soybean lecithin (SBL), used as a phospholipid source in larval fish diets, may compromise growth and survival in marine species, and affect gene expression, due to differences in fatty acid composition relative to marine lecithins (ML). The potential of SBL as a phospholipid source in gilthead seabream microdiets as compared to ML was evaluated. Two stocking densities were tested in order to exacerbate possible dietary effects: 5 and 20 larvae L−1. Larvae reflected dietary fatty acid profiles: linoleic acid was higher, whereas eicosapentaenoic and arachidonic acids were lower in SBL fed groups than in ML fed larvae. Highest stocking density decreased survival, and led to elevated saturates and lower docosahexaenoic acid levels in polar lipid. Muscle histology observations showed hindered growth potential in SBL fed larvae. Despite similar cortisol levels between treatments, higher glucocorticoid receptor (GR), as well as hormone-sensitive lipase (HSL) mRNA levels in SBL fed groups revealed a role for fatty acids in gene regulation. Further analysed genes suggested these effects were independent from the hypothalamus-pituitary-interrenal axis control and the endocannabinoid system. Cyclooxygenase-2 and gluconeogenesis seemed unaffected. For the first time in fish, a link between dietary lecithin nature and HSL gene transcription, perhaps regulated through GR fatty acid-induced activation, is suggested. Enhanced lipolytic activity could partly explain lower growth in marine fish larvae when dietary ML is not provided.This study was funded by Consejería Innovación, Ciencia y Empresa, Junta de Andalucía (Spain) which is co-financed by FEDER (project P06-AGR-01697 to M. Yúfera). Publication benefits from participation in LARVANET COST action FA0801.Peer reviewe

Effects of partial or total fish meal replacement by agricultural by-product diets on gonad maturation, sex steroids and vitellogenin dynamics of African catfish (Clarias gariepinus)

The establishment of the first sexual maturation was characterized in African catfish (Clarias gariepinus) in order to study the efficiency of replacement of fish meal (FM) by diets composed of local vegetable ingredients. Four diets were formulated containing decreasing levels of FM (50-0% for diet 1 to diet 4) and increasing proportions of vegetable ingredients (50-100%). Gonadosomatic index (GSI), diameter and percentages of developmental stages of oocytes, plasma sex steroids and vitellogenin dynamics were investigated from February to June using one-year-old fish. Fish were individually tagged, and 12 individuals from each diet were investigated monthly. Replacement of FM with plant ingredients did not affect the GSI neither in males, nor in females. All males were spermiating, and no abnormal gonads were found. In females, GSI and percentages of advanced stages of oocytes decreased during the dry season, indicating seasonal changes in gonad development. Moreover, oocytes were in late exogenous vitellogenesis, but no final maturation stages were observed, whatever the diet. Higher plasma levels of E2 in females and of androgens (T and 11-KT) in both sexes were observed in fish fed diet 4 than in those receiving diet 1 depending on the season. Levels of plasma E2 and ALP (indicator for vitellogenin) in males did not differ among treatments and seasons suggesting no phytoestrogenic activity. The results showed that total replacement of FM by vegetable diets composed of groundnut oilcakes, bean and sunflower meals has no deleterious effect on the onset of sexual maturation in African catfish but, may stimulate the sex steroid production and in turns may potentially exert some positive actions on reproductive success