Isochrysis sp. microalgae in diets for different farmed stages of the greater amberjack (Seriola dumerili)

Abstract

Aquaculture is, so far, the faster growing farming sector in the world during last decades, being sustainability and species diversification among its key development challenges. The greater amberjack, Serio/a dumeri/i, has the second longest history as a farmed Seriola species, behind the Japanese yellowtail, Serio/a quinqueradiata. The greater amberjack is an epipelagic and ephibenthic species globally distributed in warm waters, which increased farming interest due to its high growth rates compared with other marine fish cultured species. 1ts culture started in the Mediterranean region in the second half of the 1980s. Nowadays nutrition knowledge and feed improvement, from its larval stage to its full development as an adult, plays a determining role in the development of the greater amberjack culture. 1n the present study, the potential use of the microalgae lsochrysis sp. and its by- product were evaluated as novel feed ingredient in diets for different greater amberjack life cycle in order to study the most appropriate level of the microalgae in diet life stages and the effect on the fish tissues biochemical composition. Three experiments were designed based on the growth stage of the fish, and seven different diets were tested for 30, 30 and 28 days, respectively. For the M1 trial; 3%, 5% and 10% of microalgae lsochrysis sp. (1S0}; For the M2 trial; 3%, 6% and 12% of by-product (C0-1S0} and 3% of microalgae lsochrysis sp. ; and for the M3 trial; 3%, 6% of by-product (C0-1S0}, 3% of microalgae lsochrysis sp. and 3% of agro-industrial residue from red wine (C0-WG}. Fry amberjack biochemical composition reflects a relation between 1S0-3% and 1S0-5% showing a lipid reduction in whole body and gut and a similarity in liver fatty acids and biochemical composition instead. Larvae stage diet had an impact on the composition of fatty acids and therefore on the digestion process due to the wider accessibility of the by-product compared to the raw microalgae showing an inverse relationship between SFA, MUFA and omega-3 fatty acids, and besides, a skin pigmentation was generated due to the incorporation of 1S0. 0n-growing amberjack did not show different between diets but although higher MUFA content and a reduction of n-3 polyunsaturated fatty acids were reflected. This study confirms that 1sochrysis biomass can be used up to a maximum level of 5% as dietary ingredient in feeds for fry amberjack (Trial M1} and the C0-1S0 by-product up to a level of 6% in larval stages (Trial M2} as in fattening stages (Trial M3}.