EVALUATION OF PARTIAL REPLACEMENT OF FISHMEAL AND FISH OIL BY MICROALGAE EXTARCTS IN DIETS FOR HYBRID STRIPED BASS Morone chrysops × Morone saxatilis

Aquaculture production has intensify in recent years resulting in increased demand for ingredients of marine origin in aquafeeds. This has caused steadily increasing aquafeed prices ranging from 20-40%. Many strategies have been implemented to reduce costs of aquafeeds including replacement of fishmeal (FM) and fish oil (FO) with alternative ingredients. Thus, two comparative feeding trials of 6 weeks duration were conducted to investigate the effects of FM and FO replacement with different types of microalgae in the diet of juvenile hybrid striped bass (HSB) (average initial weight of 10.6 g/fish). A control diet was formulated to contain 40% crude protein (CP), with equal contributions from FM and SPC as the protein sources, and 10% crude fat, using FO as the main lipid source. The microalgae evaluated in feeding trial 1 (F1) to partially replace FM and soy protein concentrate (SPC) included lysed extracted Nanochloropsis salina (LENS) meal and mixed culture of Phaeodactylum tricornutum and Nanochloropsis salina (PTNS) meal. In feeding trial 2 (F2), the heterotrophic algae Arthrospira sp. and Schizochytrium limacinum was used to partially replace FM, SPC and FO. The algae products were substituted to replace either 25% or 50% of the total CP % in F1. In F2, combinations of meals from Arthrospira and Schizochytrium limacinum was used to replace 10, 20, 30, 40 and 50% of FM and SPC in the control diet.

Results showed that replacing CP in the control diet with LENS and PTNS in F1 had a significant effect within the treatment groups on weight gain (WG) of the fish (P< 0.05) (Fig 1). Similarly, substitution of FM, SPC and FO with Arthrospira sp. and Schizochytrium limacinum had significant effects on WG (P<0.05) (Fig 2); however, no significant differences in feed efficiency ratio (FER) were evident. No significant differences was observed in whole-body proximate composition and fish had 100% survival in both trials. In conclusion, LENS was able to substitute 25% of protein from FM and SPC without adversely affecting WG in F1, and in F2, substitution of Arthrospira sp. and Schizochytrium limacinum up to 50% of the FM and SPC improved WG of the fish.