The objective of the present study was to determine the effect of Se inclusion in high-DHA and vitamin E microdiets (5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight; 5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight supplemented with Se) in comparison with a control diet (1 g DHA/100 g dry weight and 150 mg vitamin E/100 g dry weight) on sea bass larval growth, survival, biochemical composition, malonaldehyde (MDA) content, muscle morphology and antioxidant enzymes (AOE), insulin-like growth factors (IGF) and myosin expression. For a given DHA and vitamin E dietary content, Se inclusion favoured larval total length and specific growth rate, and reduced the incidence of muscular lesions, MDA contents and AOE gene expression. In contrast, IGF gene expression was elevated in the 5/300 larvae, suggesting an increased muscle mitogenesis that was corroborated by the increase in mRNA copies of myosin heavy chain. The results of the present study denoted the beneficial effect of Se not only in preventing oxidative stress, as a glutathione peroxidase cofactor, but probably due to other as yet unknown physiological functions.

The effect of the feeding period on larval development was investigated in European sea bass larvae by considering the expression level of some genes involved in morphogenesis. Larvae were fed a control diet except during three different periods (period A: from 8 to 13d post-hatching (dph); period B: from 13 to 18dph; period C: from 18 to 23dph) with two compound diets containing high levels of vitamin A or PUFA. European sea bass morphogenesis was affected by these two dietary nutrients during the early stages of development. The genes involved in morphogenesis could be modulated between 8 and 13dph, and our results indicated that retinoids and fatty acids influenced two different molecular pathways that in turn implicated two different gene cascades, resulting in two different kinds of malformation. Hypervitaminosis A delayed development, reducing the number of vertebral segments and disturbing bone formation in the cephalic region. These malformations were correlated to an upregulation of retinoic acid receptor γ, retinoid X receptor (RXR) α and bone morphogenetic protein (BMP)4. An excess of PUFA accelerated the osteoblast differentiation process through the upregulation of RXRα and BMP4, leading to a supernumerary vertebra. These results suggest that the composition of diets devoted to marine fish larvae has a particularly determining effect before 13dph on the subsequent development of larvae and juvenile fish.

This paper describes the suitability of a closed recirculation system to study the development of fish larvae in a strictly controlled environment, where only feeding was varied (fed, starved, delayed and late fast treatments). The system served both as an incubator and hatchery. The time variation of physical and chemical parameters together with survival and growth of reared sea bass larvae (Dicentrarchus labrax) were studied over the first month of life. The recirculation design allowed for the maintenance of levels of ammonia, nitrite and nitrate below those cited as responsible for mortality or decreased feeding ability in other marine fish larvae. Almost no larval mortality occurred in the fed larvae from day 9 after hatching. The starved group of larvae showed a sharp decline in survival after 16 days of food deprivation. Larvae for which feeding was delayed until day 13 ceased dying 4 days after food was supplied. Fast feeding on days 24 and 25 had no effect on larval survival. Growth in length was similar during the first 2 weeks of larval life regardless of feeding treatment. Two days of late fast had no effect on larval growth. Growth patterns of fed larvae in this study were similar to those reported for larvae reared in flow through systems. We believe that survival and growth of the reared larvae was a direct function of diet, and that the type of rearing system did not adversely affect these parameters. The rearing design and the results obtained suggest that future nutritional studies of field-collected larvae will benefit from this kind of rearing experiment.