EVALUATION OF MICROALGAE CONCENTRATES AS FISHMEAL REPLACEMENTS FOR HYBRID STRIPED BASS Morone sp. INCLUDING EFFECTS ON NUTRIENT DIGESTIBILITY, GROWTH AND UTILIZATION OF FEED

The rapid growth of aquacultural production has resulted in an increasing demand for aquafeeds. Currently, the feed industry is progressively finding alternative ingredients especially to replace fishmeal [FM] due to its steadily increasing price due to heightened demand as aquaculture continues to grow. The use of processed microalgae concentrates in aquafeeds in recent years have been considered to be potentially viable alternatives to FM and fish oil. However, considering FM has an ideal amino acid profile for most cultured species, it is more feasible to partially replace FM with microalgae concentrates. The nutrient digestibility and utilization of microalgae ingredients have not been determined for hybrid striped bass. Therefore, the objectives of this study were to evaluate several microalgae concentrates in hybrid striped bass diets and their effects on weight gain, feed utilization and nutrient digestibility.

A comparative feeding trial was conducted to evaluate the replacement of FM with different types of microalgae in the diet of juvenile hybrid striped bass (average initial weight of 15.1 g/fish). The microalgae evaluated included dried products from monocultures of Phaeodactylum tricornutum and Nanochloropsis salina, as well as mixed cultures of those two species. In addition, several preparations of Chlorella sp. extracted by various means and bluegreen algae biomass were evaluated. All diets were kept isonitrogenous at 40% CP and isocaloric at 3.3 kcal digestible energy g^-1. The reference diet was formulated to contain an equal amount of protein from Special Select menhaden FM and soy protein concentrate. The various algae products were substituted to replace either 10 or 20% of the protein in the reference diet. The feeding trial was conducted in a recirculation system where 15 fish were stocked into 110- L glass aquaria. All treatments were triplicated and fish were fed twice daily at a rate approaching apparent satiation for 8 weeks.

No mortality was observed during the feeding trial, but growth performance of hybrid striped bass was affected by dietary treatments.  Fish fed the reference and bluegreen algae diets has similar weight gain which was significantly greater than that of fish fed diets in which the algae products were included. Substitution of the other algae meals tended to reduce weight gain by 10 to 17% compared to that of fish fed the reference diet. There are many other analysis currently underway such as protein and amino acid digestibility which will be presented.