Characterization of methionine uptake and clearance in the hemolymph of Pacific white shrimp Litopenaeus vannamei

Abstract

A series of feeding trials were conducted to investigate the absorption rate of amino acids and compare the absorption of different methionine (Met) sources in the hemolymph of Pacific White shrimp, Litopenaeus vannamei. In trial 1, a basal diet was supplemented with three alpha amino acids including DL-Met, lysine and arginine and the beta amino acid taurine. Shrimp were fed with test diets for 30 mins and then the leftover feeds were withdrawn. The hemolymph samples were taken every 30 mins over 5 h after feeding to determine amino acid (AA) concentrations in the hemolymph. Results indicated that total AA, Met and Lys were near their peak after feeding 30 mins and the level declined within 60 mins to near fasting levels. No secondary peaks were observed for any AA. The diet supplemented with AA exhibited higher peaks than the basal diet. The second and third trials focused on the identification of different patterns that would indicate asynchronous absorption and comparison of the absorption of different Met sources. Four experimental diets were produced, including a basal diet (soy protein-based), a DL-Met-supplemented, a dipeptide Met (Met-Met)-supplemented, and a high fishmeal diet (high-Met intact protein) in trial 2. Fasted shrimp were offered diets for 15 mins and then the leftover feeds were removed. The hemolymph samples were taken every 15 mins over a 1 h period after feeding. The results generally confirmed the fast absorption and clearance of AA in shrimp and indicated that the diets containing different Met sources resulted in higher Met levels in the hemolymph as compared to the basal diet. To better define the absorption process and confirm if there may be a synchronous peak during absorption, the third trial simply looked at the uptake of AA over a 1 h period with basal diet and dipeptide Met diet. The shrimp were offered diets for a total of 60 mins during this timeframe intermittent samples were taken at 0, 5, 10, 15, 20, 30, and 60 mins. Results demonstrated the pattern for AA uptake is similar with a clear upswing in AA levels in 10–15 mins after the initiation of feeding. Based on both absorption and clearance patterns of the amino acids, we demonstrated that there were no indications of asynchronous absorption of supplemented amino acids; hence, supplemented amino acids are available for metabolism. In addition, the data also demonstrated higher peak of Met over time in the hemolymph of L. vannamei with the Met-Met supplemented diet versus the DL-Met supplemented diet.