SOYBEAN AND LUPIN SEED MEALS AS PROTEIN-SOURCES IN DIETS FOR GILTHEADSEABREAM (SPARUS-AURATA) - NUTRITIONAL AND HISTOLOGICAL IMPLICATIONS

The use of vegetable protein sources in diets for freshwater fish has been studied in more detail than for marine fish species. Two experime nts were conducted to compare the effect of the partial substitution o f fish meal by two different vegetable protein sources, soybean and lu pin seed meals. Mean feed intake and growth were not significantly inf luenced by type or level of plant protein in the diet. Feed utilizatio n indexes such as feed efficiency, protein efficiency ratio and protei n productive values were not significantly affected by the type of pla nt protein in the diet, although a general reduction of these values w as observed with increased inclusion of soybean meal. Histological stu dies showed an increased deposition of lipid and decreased glycogen de posits in the liver with increased levels of dietary soybean meal. Pro tein digestibility coefficients for lupin seed meal diets were similar to the control and 10% higher than those for the soybean meal diets. A significant reduction in trypsin activity was observed in fish fed t he lupin seed meal diets, and for soybean meal diets when the substitu tion level reached 30%. Diets including plant protein showed a higher peak of ammonia excretion rate, which appeared 2 h later than that of the fish meal diet. Highest values of dissolved ammonia were registere d in fish fed a soybean meal-based diet. These results suggest that pr operly treated lupin meals could be an important alternative dietary p rotein source for gilthead seabream.