Influence of dietary concentrations of protein, lipid and carbohydrate on growth, protein and energy utilization, body composition, and plasma titres of growth hormone and insulin-like growth factor-I in non-transgenic and growth hormone transgenic coho salmon, Oncorhynchus kisutch (Walbaum)

This study compared the ability of juvenile non-transgenic (NT) and transgenic growth hormone (T; gene construct OnMTGH1) coho salmon (Oncorhynchus kisutch) to metabolically utilize energy from lipid and carbohydrate for growth at two dietary protein concentrations. Triplicate groups of size-matched (initial weight, 28.2-29.1 g) NT and T salmon held in 10.5-10.8 ...C well water on a natural phototocycle (12.25 h ... 8.25 h) were each fed one of four isoenergetic (~ 17.5 MJ of digestible energy (DE)/kg) dry diets twice daily to satiation for 83 days. These diets contained 340 g (LP) or 430 g (HP) of estimated digestible protein (DP)/kg and either 123 g (LL) or 164 g (HL) of estimated digestible lipid (DL)/kg at each DP level (dry weight basis). Estimated digestible carbohydrate (DCHO) concentrations ranged from 45 to 269 g/kg to equalize dietary DE. Under the preceding conditions 46-66% of NT and 18.7-27.5% of T coho, depending upon diet treatment, exhibited no growth or lost weight during the study. NT coho are known to grow slowly or lose weight between the fall equinox and winter solstice but this was unexpected for T coho. Considering all fish T coho, regardless of diet treatment, exhibited significantly higher specific growth rates (SGR) than NT fish due to enhanced feed intake, feed and protein (gross and available deposited) utilization and generally improved available energy utilization. Diet treatment did not affect the growth performance of T fish. Within NT fish, the HP diets supported best gross and available protein and energy utilization. SGR values for growing fish (F...) only followed identical trends to those for all fish in relation to diet treatment. Regardless of fish genotype, terminal hepatosomatic indices for F... were directly related to dietary DCHO content and maximum values were noted in NT fish fed LP-LL (significantly higher than observed in NT or T fish fed HP-HL). Final whole body protein concentrations adjusted for dissimilar fish size were higher in T fish fed HP-HL than in T fish fed LP diets and NT fish fed LP-LL. This was also true for T fish fed HP-LL versus T fish fed the LP diets. Within HP groups, whole body lipid and energy contents were generally higher in NT versus T fish whereas within the LP groups energy content was significantly higher in T versus NT fish and was highest in T fish fed LP-LL. Terminal plasma titres for GH and IGF-1 (all fish) were significantly higher in T than in NT fish and were generally unin