BROODSTOCK AND LARVAE NUTRITION IN GILTHEAD SEABREAM SPARUS-AURATA - NEW FINDINGS ON ITS MODE OF INVOLVEMENT IN IMPROVING GROWTH, SURVIVAL AND SWIMBLADDER INFLATION

Larvae growth and survival of gilthead seabream (Sparus aurata) can be improved through better understanding of their nutritional requiremen ts. In the last decade or so, we dwelled mainly on the fatty acid requ irements of seabream larvae. The n-3 highly unsaturated fatty acid (HU FA) requirements are age dependent, being 4 mg per g (DW) rotifer (Bra chionus plicatilis) at stages up to 250 mu g DW (22 days of age). Beyo nd this size, the requirements increase dramatically to 29.8 mg per g (DW) Artemia nauplii, possibly because of the tripling of the Artemia lipid content. Supply of this level of n-3 HUFA in early larvae was as sociated with a growth acceleration of 250% as compared with a low die tary supply of 0.8 mg n-3 HUFA per g (DW) rotifer. Moreover, like othe r marine fish, seabream has a preference for docosahexaenoic acid (DHA ) over eicosapentaenoic acid (EPA) for both growth and survival. Our s tudies on seabream eggs and larvae show that these essential fatty aci ds (EPA+DHA) are incorporated preferentially into polar lipids and par ticularly into phosphatidyl choline and phosphatidyl ethanolamine as p art of the biomembrane. In addition to optimizing larvae growth and su rvival via the larvae diet, these factors were further improved throug h broodstock nutrition. Larvae growth, survival and swimbladder inflat ion are directly affected by the composition of the diet of the broods tock. We found that both protein and lipid fractions in squid meal pla y an important role in improving the fecundity and egg quality. A diet ary inclusion of 5 mg n-3 HUFA per g diet was associated with over 80% of the larvae having a functional swimbladder as compared with 55% in broodstock fed soy oil. A further increase to 15 mg n-3 HUFA per g di et was associated with a 30% increase in daily larvae growth. For the best response of seabream broodstock, a 49% balanced protein diet with 15 mg n-3 HUFA per g is required. Being a daily spawner, it takes no more than 15 days for seabream to fully respond to the dietary change in terms of egg composition and viability. The protein fraction of squ id meal has a significant effect on the egg quality of gilthead seabre am. This is because the amino acid composition of squid is similar to that of the seabream egg. The presence of a balanced composition of es sential amino acids expressed itself in vitellogenin synthesis and sel ective uptake through receptor mediated endocytosis. In conclusion, gr owth and survival of larvae are the key to future mass production of f ish in mariculture. Only a combination of basic and practical research in both phases, of oocyte buildup and a larvae development, will insu re it.