Feed intake, gastro-intestinal transit and haemolymph free amino acids in the shrimp Penaeus monodon are influenced by marine meal supplementation

Aquaculture production can be improved by understanding how ingredients can affect feed intake and digestion. This is an area poorly understood for many aquaculture species, including for the shrimp Penaeus monodon. To investigate these processes, we measured feed intake, the rate at which digesta moves through the gastro-intestinal tract, the change of free amino acids (FAA) circulating in the haemolymph following feeding, and how different test ingredients affect these processes in this species. Diets supplemented with microbial Novacq™ (NQ), krill meal (KM) or whole squid meal (SQ) and a control diet were used across two separate experiments. In the first, feed intake was measured in communally housed shrimp for 60, 120 and 360 min to examine the effects of diet on ingestion. Feed intake after 360 min was greater in shrimp offered the SQ diet while no effect was observed at earlier time points. In the second experiment, individually housed shrimp were used to measure feed intake, the rate at which digesta passed through the gut and the change of individual FAA in the haemolymph over a 30 min period. For this experiment, addition of SQ and NQ increased both the rate at which digesta travels through the gut and post-prandial concentration of FAA in haemolymph at 5 min. Krill meal had the highest haemolymph concentration of amino acids at 10 min and all dietary treatments showed a convergence of haemolymph FAA by 30 min. The different ingredients appear to affect the appearance of FAA in haemolymph through different mechanisms. For SQ, the FAA content of the diet was high, being 2.8 times that of the others (27.6 vs. 10.0 g kg−1), and it is hypothesized that the availability of these FAA resulted in the rapid increase in haemolymph observed for this treatment. In contrast, two other ingredients also led to rapid increases in haemolymph FAA. However, for these diets the amount of FAA present was similar to the control indicating that other characteristics of the meals may be causal. Our data indicate that specific ingredients can increase both the rate at which digesta travels through the gut and the rate of absorption of amino acids and that these mechanisms could explain increases in both feed duration and intake.