INTERACTIVE DIETARY EFFECTS OF CARBOHYDRTATE AND LIPID LEVELS IN THE PRESENCE OR ABSENCE OF BILE ACID ON LARGEMOUTH BASS Micropterus salmonides PERFORMANCE

Fish oil is the preferred source of oil in fish feeds as it is high in ω -3 fatty acids like EPA and DHA. However, fish oil is a finite resource that needs to be reduced or replaced in fish feeds by using sustainable alternatives. Carnivorous species like largemouth bass (Micropterus salmonides) are metabolically adapted to low dietary carbohydrate (CHO) utilization, thus, diets containing more CHO can reduce their growth performance. Therefore, the goal of this study was to induce higher CHO utilization in largemouth bass by reducing lipid inclusion in the diets and assessing whether dietary bile acid (BA) supplementation could enhance lipid utilization. Hence, three variables were the subject of study: lipid and CHO inclusion level and bile acid supplementation. A total of 8 isonitrogenous (40% crude protein) diets were formulated: 4 diets containing  9% lipid (low, L) and the other 4 diets having 12% lipid (high, H); both 9% and 12% combined each of the following diets: 1- low CHO (20%) + 0% BA; 2- low CHO (20%) + 1.5% BA; 3- high CHO (30%) + 0% BA; 4- high CHO (30%) + 1.5% BA. A total of 480 fish initially weighing 6.0 g average were randomly distributed into 24 tanks (20 fish per tank) and fed each respective diet for 8 weeks.

Results show that performance of fish was highest in diet 7 (H-CHO + L-lipid + BA), which was statistically similar to diet 1 (control) (Fig 2). Feed conversion ratio was unaffected by dietary treatments, whereas feed intake was significantly affected.

Liver histopathology showed that the combination of H-CHO (30%) and H-lipid (12%) (diet 2) led to extensive vacuolization and granulomas. However, H-CHO (30%) and L-lipid (9%) supplemented with BA mitigated these adverse effects. Genes expression profile related to carbohydrate and lipid metabolisms are being analyzed in the liver and muscle, which will be presented. Overall results indicate that lipid can be reduced by increasing the inclusion of CHO in the presence of BA supplementation for largemouth bass diet.