Utilization of waste material resulting from trout processing in gilthead bream (Sparus aurata L.) diets.

Fish processing creates a large amount of waste of high nutrient content which, if not properly processed for use in human or animal nutrition, is likely to be deposited in the environment creating pollution problems. Waste parts from rainbow trout processing for smoking, consisting of heads, bones, tails and intestines, were used as feed ingredients for gilthead bream diets. Heads, bones and tails had similar compositions, their weighed mean indicating about 700 g kg[sup -1] moisture, 150 g kg[sup -1] protein and 110 g kg[sup -1] fat. Intestines contained higher lipid (350 g kg[sup -1]) and lower moisture (560 g kg[sup -1]) and protein content (80 g kg[sup -1]). Seasonal changes in composition indicated significant differences. Three experimental diets were formulated having the same proximate composition on a dry weight basis. The control diet (A) contained fish meal as the main protein source and fish oil as the oil supplement. In diet B part of the protein and most of lipid was provided by trout waste and in diet C most of the lipid was provided by trout intestines. Gilthead bream fingerlings of 4 g initial weight were fed to apparent satiation for 72 days, at a temperature of 20 °C, to an average final weight of 19 g. All diets were fed in a dry form. The experiment was performed in duplicate. Growth and feed utilization data were high and similar among groups. The body composition of the resulting fish did not show any difference among dietary treatments. Differences in liver lipid and fatty acid content were found between all dietary treatments. The growth and body composition data from this preliminary experiment indicated that trout waste could be used successfully as a dietary ingredient of sea bream diets. [ABSTRACT FROM AUTHOR]