The aim of this study was the evaluation of microalga Isochrysis sp. T-Iso in partial substitution of fish meal and the study of the effects on gilthead sea bream (Sparus aurata) performances and chemical composition of fillets. The results show that the microalga T-Iso nutrients support growth better than control diets, and the chemical composition of sea bream fillets also meets the needs of consumers for healthy diets. T-Iso resulted highly digestible, and support the best performances of fish fed on 70% alga diet probably due to its high protein efficiency in comparison to other diets. The presence of a high quantity of cyclic isoprenoid could explain this high efficiency of T-Iso.
Gilthead sea bream fed on 70% T-Iso showed fillets with a low level of protein and a high level of fat; moreover, their somatic indexes were higher than those of fish fed other diets. Highest percentage TIso diet showed the highest amount of the sum of saturated fatty acids, mainly due to myristate and palmitate. On the contrary, the sum of polyunsaturated decreases, mainly because of the reduction of EPA and DHA amounts. If the mass production economical problems are solved, T-Iso will represent a good solution in partial substitution of fish meal.
The current trend in fish farming is towards increased use of plant protein in commercial fish diets. In the last decade, much more attention has been paid to plant source of protein (Palmegiano et al., 2006). Microalgae are increasingly being used as feed in aquaculture for many marine organisms, because they constitute a source not only for energy, but also of many essential compounds such as the polyunsaturated fatty acids (Belay et al., 1996). The possible use of microalgae has been investigated as a nutrient for fish larvae as well as for juveniles and adults (Lu and Takeuchi 2004; Palmegiano et al., 2008). Among those algae, Isochrysis sp. showed to have high quality of nutrients (CP: 43.0; EE: 18.7; Ash: 10.1; Crude fiber: 0.9; Total starch: 10.4 (99% gelatinized) and to be a good source of polyunsaturated fatty acids and in particular docosahaesenoic acid (DHA) (Trotta,1998). The aim of this study was to evaluate a microalga (Isochrysis sp. T-Iso) as source of plant protein and ether extract in partial substitution of fish meal and fish oil, studing its effects on gilthead sea bream (Sparus aurata L.) performances and chemical composition of fillets.