Partial sustitution of fish oil for microalgae in strater diets for gilthead seabream "Sparus aurata"

Abstract

Fish oil is a limited source and will not be able to cover the required quantity needed for the aquaculture developmen1. In this context, two types of microalgae Crypthecodinium cohnii and Phaeodactylum tricornutum were used to partially substitute the fish oil content in starter diets for gilthead sea bream one of the marine fish highly produced in different countries of Europe. Five experimental diets with different sources of lipid were used: diet EPAX (where 2% of fish oil was substituted by EPAX); diet Fa (control diet containing only fish oil); diet 2 % C. c (where 2% of C. cohnii was added as a partial alternative of fish oil); diet 4 % C. c (where 4% of C. cohnii was added as a partial alternative of fish oil) and diet Ph. t (where Up to 5% of P. tricornutum was added as a partial alternative of fish oil). These diets were tested in rearing of the gilthead seabream Sparus aurata (initial weight 73 mg) in order to evaluate survival, growth, specific growth rate, body chemical composition, body fatty acid composition and morphological changes in lipid liver content and intestinal lipid absorption. The experiment was divided in two sub-periods according to feeding size and fish weigh1. Results were showed after 27 days of feeding (the first period) that those fish fed 4 % C. and 2 % C. c diets did not demonstrate difference in growth with the fish fed control die1. Different growth were observed between the first and the second period (57 days of feeding) in which the fish fed Ph. t diet did not demonstrate difference in growth with the fish fed 2 % C. c, 4 % C. c and Fa diets. There is no difference among treatment in the biomass; In the end of the experiment the fish fed 2 % C. c , 4 % C. c and EPAX diets observed the high survival rate with significant difference ( P< 0.05%) with fish fed diet Fa and diet Ph. 1. In the end of the experiment also the fish fed microalgae diets increases its content of DHA, EPA, AA and n-3HUFA and reach the similar level ofthe fish fed control diet after two months. Anterior intestine of the fish fed Ph. t diet observed epithelial degeneration, thus pathological studies should be needed to clarify degeneration causes, the same treatment observed the highest hepatocytes lipid content among aH treatments. The degeneration observed in the epithelial of anterior intestine in fish fed Ph. t diet may be affect negatively the survival rates and more studies should be needed to clarify this effect. Determination of the adequate absolute quantity and different ratio of the different fatty acids is the most important criteria to choose the adequate type of microalgae to obtain good results. In conclusion partial substitution of fish oil by microalgae Crypthecodinium cohnii and Phaeodactylum tricornutum may be adequate for gilthead seabream aquaculture.