BEHAVIORAL ASSAYS DEMONSTRATE HOW KRILL MEAL ENHANCES ATTRACTABILITY & PALATABILITY OF FEED PELLETS FOR PACIFIC WHITE SHRIMP Litopenaeus vannamei  

Charles Derby1,*, Farida Elsayed1, Samantha Williams1, Christian González1,
MiNa Choe1, Anant Bharadwaj2, and George Chamberlain2
 
1Neuroscience Institute & Dept Biology, Georgia State University, Atlanta, cderby@gsu.edu  2Integrated Aquaculture International, St. Louis, MO, USA

Pacific white shrimp, Litopenaeus vannamei, is a major species in world-wide aquaculture. L. vannamei is commercially grown on feed that often contains plant protein as a nutritional source, which is advantageous over marine protein in cost and sustainability. However, compared to marine protein, plant protein is less attractive and palatable to shrimp. Thus, maintaining an acceptable growth rate for shrimp without marine protein requires using more feed, resulting in feed waste and lower profitability.  The goal of our research program is to identify feed additives that increase the attractability and palatability of feed pellets, and to characterize underlying mechanisms. The focus of the study reported here is krill meal. In our first experiment, we used an 'attractability assay' to show that an aqueous extract of krill meal induced group-housed shrimp to move toward, probe, and grab its release site (an airstone) in a concentration-dependent manner, thus defining the attractability of krill meal itself. In our second experiment, using a 'palatability assay,' we tested the ability of krill meal to enhance the attractability of feed pellets (30% soybean meal, 27% marine-protein-free feed concentrate, 34% wheat flour) into which krill meal was incorporated at 1, 3, or 6%. An aqueous extract of feed pellets was significantly more attractive to shrimp if the pellets contained krill meal, and the effect of krill meal was concentration dependent. However, this effect did not occur for 5-min rinses of pellets, but rather required longer extraction. In a third set of experiments, addition of krill meal to pellets enhanced the pellets' palatability. For individually-housed animals that were sequentially offered single pellets until they stopped ingesting, consumption (measured as either the total number or total weight of pellets eaten) was greater for krill meal-containing pellets than basic pellets. This effect was due to shrimp eating more pellets rather than eating faster, except for pellets containing 6% krill meal for which they ate the first two pellets faster than they did pellets containing 3 or 1% krill meal. Krill meal also enhanced the amount of food eaten by group-housed animals, in 1-hr and 3-hr assays. The effect of added krill was greater in 3-hr than 1-hr assays. Taken together, our results show that krill meal is a chemoattractant whose major effect when added to our pellets, at least as they were fabricated, is to increase the pellets' palatability more than in increasing attractability. Our experimental approach should be useful in developing chemostimulatory feed additives for L. vannamei and other cultured species.