| dc.description.abstract | A series of in vitro and in vivo studies were conducted to determine: (1) the relative importance of amino acids (AAs), fatty acids and glucose as metabolic fuels for tissues of largemouth bass (LMB, a carnivorous fish); and (2) the optimal requirements of LMB for dietary protein, lipids and starch; and (3) the feasibility of replacing dietary fishmeal with alternative animal- and plant-source protein feedstuffs. Results of the first study (Chapter II) indicated that glutamate, glutamine and aspartate were oxidized at higher rates than glucose and palmitate for ATP production in the proximal intestine, liver, kidneys, and skeletal muscle of LMB. All the tissues had high activities of phosphate-activated glutaminase, glutamate dehydrogenase, and glutamate transaminases. Glutamine, glutamate and aspartate together generated 60-70% of ATP in LMB tissues and supported most of their oxygen consumption. Findings from the second study (Chapter III) demonstrated that the rates of glutamate and glutamine oxidation in these tissues were regulated by dietary protein intake in a tissue-specific manner to meet their metabolic needs. The fish had particularly high requirements for dietary protein to primarily satisfy their needs for glutamate, glutamine and aspartate as energy sources and minimize the hepatic accumulation of glycogen. Feeding experiments revealed that increasing the dietary crude protein content from 40% to 50% improved the growth performance and liver morphology of LMB (Chapter VI) and that excess dietary levels of starch (≥ 10%) resulted in hepatic glycogenosis (Chapter V). This metabolic disorder was due to the limited utilization of glucose by tissues and prolonged elevations of blood glucose for glycogen synthesis in the liver. Based on growth, metabolic and histologic data, we recommend dietary crude protein (CP), lipids and starch levels to be 45%, 10% and < 10%, respectively, for juvenile LMB. Data from Chapter VI showed that 15% fishmeal protein (dry matter basis) in the diet could be replaced by low-cost poultry by-product meal plus soybean meal without affecting growth rates and feed efficiency of LMB. However, this practice resulted in inadequate provision of methionine and taurine, and black skin syndrome characterized by not only black spots in the skin but also damage in the eye, intestine and liver. In the final experiment (Chapter VI), supplementation with 0.5% methionine to low fishmeal diets improved the growth performance, feed efficiency, and health of LMB, while reducing the incidence of black skin syndrome in the fish from 38% to 10%. Collectively, findings from the current study not only advance basic knowledge on the nutrition, metabolism and functions of AAs in fish species, but also provide data for developing next generation of practical feeds for LMB to improve the efficiency of their growth and sustain their global production. | |
