Effect of several feeding stimulants on diet preference by juvenile gibel carp ( Carassius auratus gibelio), fed diets with or without partial replacement of fish meal by meat and bone meal

Abstract

The objectives of this work were to study the effects of several feeding stimulants on gibel carp fed diets with or without replacement of fish meal by meat and bone meal (MBM). The feeding stimulants tested were betaine, glycine, l-lysine, l-methionine, l-phenylalanine, and a commercial squid extract. Three inclusion levels were tested for each stimulant (0.1%, 0.5%, and 1% for betaine and 0.1, 0.25 and 0.5% for the other stimulants). Two basal diets (40% crude protein) were used, one with 26% fish meal (FM), and the other with 21% fish meal and 6% MBM. Betaine at 0.1% in the fish meal group and at 0.5% in the meat and bone meal group was used in all experiments for comparison among stimulants. In the experiment on each stimulant, six tanks of fish were equally divided into two groups, one fed the FM diet, and the other fed the MBM diet. After 7 days' adaptation to the basal diet, in which the fish were fed to satiation twice a day, the fish were fed for another 7 days an equal mixture of diets containing varying levels of stimulants. Each diet contained a unique rare earth oxide as inert marker (Y 2O 3, Yb 2O 3, La 2O 3, Sm 2O 3 or Nd 2O 3). During the last 3 days of the experiment, faeces from each tank were collected. Preference for each diet was estimated based on the relative concentration of each marker in the faeces. Gibel carp fed the FM diet had higher intake than those fed the MBM diet, but the difference was significant only in the experiments on betaine, glycine and l-methionine. None of the feeding stimulants tested showed feeding enhancing effects in FM diets. All feeding stimulants showed feeding enhancing effects in MBM diets, and the optimum inclusion level was 0.5% for betaine, 0.1% for glycine, 0.25% for l-lysine, 0.1% for l-methionine, 0.25% for l-phenylalanine, and 0.1% for squid extract. The squid extract had the strongest stimulating effect among all the stimulants tested.