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Nutritional Roles of Glutamate and Glutamine in the Growth of Juvenile Hybrid Striped Bass
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Both feeding and in vitro tissue studies were conducted to test the hypothesis that glutamate (Glu) and glutamine (Gln), consisting of >10% of dry weight in fishmeal (FM), may be nutritionally essential for maximal growth and survival of juvenile hybrid striped bass (HSB) (Morone chrysops × Morone saxatilis). The first in-vitro study, using radio-labeled tracers, determined oxidation rates of Glu, Gln, leucine, glucose, and palmitate in the liver, proximal intestine, kidney, and dorsal skeletal muscle tissue that were incubated in a Krebs-Henseleit bicarbonate buffer (pH 7.4, with 5 mM D-glucose and 1 nM insulin) containing 0, 2 mM Glu, 2 mM Gln, 2 mM leucine, 2 mM palmitate, or a mixture of those nutrients (2 mM each). 14CO2 was collected to calculate the rates of substrate oxidation. Using the same solutions, the tissues’ uptake rates of each of those nutrients were also measured by counting intracellular radioactivity. The activities of some key enzymes related to the metabolism of Glu, Gln, leucine, glucose, and palmitate were also determined in the HSB tissues. The second experiment was conducted to investigate the potential of replacement of FM in HSB diets by a mixture of poultry by-product meal (PBM) and soybean protein concentrate (SPC) that contained 37% more Glu and Gln than FM. In the in vitro study, Glu and Gln were more actively oxidized in the proximal intestine, liver, and kidney of fish than the oxidation of glucose and palmitate. Together, Glu,Gln, and leucine contributed to about 80% of ATP production in fish tissues. Fish tissues had high activities of glutamate dehydrogenase (GDH), glutamate oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT) as well as high rates of Glu uptake, which provided a biochemical basis for the extensive catabolism of Glu. In the FM replacement study, up to 75% FM in HSB diet could be replaced by a mixture of PBM, SPC, and AA supplements without any adverse effect on the HSB’s growth performance. Interestingly, HSB that were fed a diet with 25-50% FM replacement with poultry by-product meal and SPC exhibited better growth performance than HSB that were fed a 60% FM diet, possibly due to the bioavailability of Glu and Gln in SPC. Collectively, results from the present study indicate that Glu and Gln are conditionally essential for the growth and health of juvenile HSB. These findings not only advance our basic understanding of AA nutrition in fish, but will also have important implications for formulating economically and environmentally sustainable aquafeeds.
Jia, Sichao (2019). Nutritional Roles of Glutamate and Glutamine in the Growth of Juvenile Hybrid Striped Bass. Master's thesis, Texas A&M University. Available electronically from