OXIDATION OF ENERGY SUBSTRATES IN TISSUES OF WHITELEG SHRIMP

The whiteleg shrimp (Litopenaeus vannamei ) is the most widely cultivated penaeid shrimp in the world. The recommended dietary protein, lipid and starch levels for this animal are about 30-40%, 5-10% and 15-20%, respectively .  Our previous study has reported that amino acids are the primary energy substrates in major tissues of some fish species.  The present study was conducted to test the hypothesis that amino acids are  also oxidized at a higher rate than carbohydrates (e.g., glucose) and fatty acids (e.g., palmitate) to provide ATP for tissues of whiteleg shrimp . The hepatopancreas , intestine, gill , and muscle were isolated from juvenile shrimp (~3.0 g) and incubated at 26 °C for 2 h in 1 ml of  modified KHB buffer (pH 7.4, with 5 mM D-Glucose )  containing  2 mM glutamate, 2 mM glutamine, 2 mM aspartate, 2 mM alanine, 2 mM leucine, or 2 mM palmitate with their respective [U-¹⁴C ]-labeled tracers . In parallel experiments , a tissue was incubated in the presence of a tracer plus a  mixture of the unlabeled substrates ( i.e., 5 mM glucose, 2 mM each of amino acids and fatty acids). ¹⁴CO₂ was collected to calculate the rates of  substrate oxidation. In the intestine and hepatopancreas ,  the rate of glutamine or glutamate oxidation  was greater  than  that of any other substrate in KHB buffer with a single energy substrate; h owever,  the rate of oxidation of aspar tate  was greater than that of any other substrate  in the presence of a  mixture of energy substrates .  In gills,  the rate of oxidation of  glucose, glutamate, glutamine or aspartate  was greater than  that of any other substrate in the presence of a single substrate or a mixture of substrates.  In  skeletal muscle, glutamine and aspartate  were the most important energy substrate in the presence of a single substrate or a mixture of substrates, respectively. In all the tissues studied, amino acids provided the most ATP, and palmitate was a minor energy substrate.   Collectively, these results indicate that  amino acids were the  major metabolic fuels for  tissues of whiteleg shrimp, as recently reported for Largemouth bass and hybrid-striped bass .  

Key Words: Whiteleg shrimp (Litopenaeus vannamei ); Oxidation; Amino acids; Glucose.