THE EFFECTS OF EXPERIMENTAL STARTER DIETS WITH DIFFERENT LEVELS OF SOYBEAN OR MENHADEN OIL ON RED DRUM (SCIAENOPS-OCELLATUS)

Red drum reared from captive-spawned eggs were used in a 2 X 4 factori al experiment comparing eight diets with soybean oil (SBO) or menhaden oil (MHO) added to a basal diet (about 3.4% lipid from practical ingr edients) at 1.5, 5.2, 9.0, or 12.7%. Triplicate groups of 20 early juv eniles (mean 0.4 g) were stocked in 1000 litre fiberglass tanks suppli ed with filtered estuarine water (17-26 degrees C, mean 22 degrees C; 15-35 parts per thousand) and hand fed twice a day to apparent satiati on for 56 days. The fish (range 0.3-9.4 g) appeared to utilize up to 1 .5-5.2% dietary SBO (in 5.4-8.7% total lipid). With 0.67% EPA + DHA (e icosapentaenoic and docosahexaenoic acids) in the basal diet, no EFA-d eficiency signs were observed. Dietary MHO was utilized up to 12.7%, b ut fish fed diets with more than 1.5% SBO had lower growth rates and i ncreased feed conversion ratios (especially with 9.0 and 12.7% SBO). D iets containing 1.5% SBO or MHO produced the leanest fish (70.5-71.6% protein, 13.0-13.1% lipid, of whole body). Diets containing 9.0 and 12 .7% MHO produced the fattest fish (64.5-66.0% protein and 19.1-19.9% l ipid). Percent liver lipid (wet) was highest far fish fed diets contai ning 5.2% SBO (41.4%), 9.0% MHO (36.5%), and 12.7% MHO (35.4%), and lo west with 1.5% MHO (24.0%). Considering the good survival, absence of disease, and excellent general health, this fatty liver condition did not appear to have short-term adverse effects. All fish in the study h ad fatty livers to some degree, and their liver histological features differed from those of wild fish. Liver lipid reserves might confer so me survival advantage to fish released for stock enhancement if the re serves are used during their transition from cultured to wild status. However, if the hepatocyte changes we observed are not reversible, lon g-term detrimental effects on liver function are possible. (C) 1997 El sevier Science B.V.