THIAMIN SUPPLEMENTATION OF DIETS CONTAINING VARIED LIPID - CARBOHYDRATE RATIO GIVEN TO GILTHEAD SEABREAM (SPARUS-AURATA L)

On the basis of their respective metabolizable energy contents, supple mental marine oil was partially replaced with a maize starch/dextrin m ixture in diets containing approximately 500 g crude protein per kg fo od thus lowering tile total dietary lipid concentration from 141.6 to 100.9 g/kg. The basal diets were then supplemented with thiamin hydroc hloride at 0.5, 5.0 and 10.0 mg/kg food to produce six test diets in a ll. After 182 days of feeding, the fish given the diets containing the higher lipid content with a thiamin supplement of 10.0 mg/kg had show n significantly better growth and food utilization (food conversion ef ficiency and apparent net protein utilization) than the fish presented with the remaining five diets. Thiamin supplements of 5 mg/kg or less resulted in poorer performance amongst the fish given the high lipid diets. The fish given all three of the low oil diets performed poorly by comparison with those given the high lipid, high thiamin diet and p erformance was comparable with that of the fish given the high lipid d iets containing thiamin at 5 mg/kg or less. Proximate carcass composit ion in terms of moisture, protein and lipid was unaffected in response to diet. Glycogen accumulation in the liver was significantly elevate d amongst the fish given the low lipid diet where the thiamin suppleme nt was 5.0 mg/kg or more. The haematology of the fish was not signific antly altered in response to diet although elevated haematocrit was as sociated with decreasing thiamin supplementation. It would appear that for the seabream, lipid and carbohydrate ave not exchangeable on the basis of their metabolizable energy content. When given high lipid die ts the thiamin requirement of the seabream is in excess of 5.0 mg/kg a nd increasing the thiamin supplement to 10 mg/kg in high carbohydrate diets made no impact on performance.