Growth performance, nitrogen balance and protein turnover of rainbow trout (Oncorhynchus mykiss (Walbaum)) under different dietary regimens

• Main Author: Perera, Withanage Mala Kanthimathi
• Published: University of Aberdeen 1995
• Subjects: 571.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.593284

This thesis presents the results of a series of experiments carried out to determine if bacterial single-cell protein (BSCP) could replace fishmeal in a pelleted diet in rainbow trout (Oncorhynchus mykiss (Walbaum)) and to investigate the quantitative lysine requirement of this species using a methodology for the measurement of individual food consumption rates viz. radiography. In the first investigation, four diets were formulated to contain a total of 45.8% crude protein of which 0% was from BSCP in BSCP-0, 25% in BSCP-25, 62.5% BSCP-62.5 and 100% in BSCP-100; the remainder of the protein being from fishmeal. Food consumption rates of individual fish were measured using radiography. The results show that 100% BSCP diet resulted in significantly higher food consumption rates but was associated with a reduction in N absorption efficiency, growth rates and N growth efficiencies when compared to the diet that contained no BSCP. The diet containing 25% BSCP did not significantly influence growth rates, food consumption or absorption efficiency when compared with a 100% fishmeal diet. Construction of N budgets demonstrated that the reduction in growth of fish eating an increasingly larger proportion of BSCP was due to a decrease in N absorption and an increase in the excretion of urea. The nutrient absorption efficiency shows that even though the four dietary groups were well balanced in terms of known amino acid requirements in trout, fish fed on the BSCP-100 diet absorbed below requirement level in respect of some amino acids due to the poor absorption efficiency of this diet.