Influence of ration level on the growth performance and body composition of non-transgenic and growth-hormone-transgenic coho salmon ( Oncorhynchus kisutch)

Abstract

Duplicate groups of size-matched (range in initial mean weight, 23.5–27.2 g) growth-hormone-transgenic (T; construct OnMTGH1) and non-transgenic (NT) juvenile coho salmon from wild (W) and commercial (COM) sources, were fed a high nutritive value steam pelleted dry diet by hand four times daily for 63 days to maximum ration (R) viz., T-R T, NT-W-R W, and NT-COM-R COM, or they were pair-fed the maximum ration ingested by NT-W fish (NT-COM-R W and T-R W) or that consumed by NT-COM fish (T-R COM). The pair-fed rations were below the maximum rations of NT-COM and T fish. All groups were provided with running (6–8 L/min), aerated (dissolved oxygen, 6.8–10.3 mg/L), 10.5–11.0 °C well water and a natural photoperiod during the study. T-R T coho had significantly higher growth rates (1.9 fold) and dry feed (2.2 fold) and digestible protein and energy intakes (1.7 fold) than noted for NT-W-R W and NT-COM-R COM fish. Moreover T-R T coho, unlike pair-fed T coho and all NT groups, did not show a body weight or seasonal decline in growth rate during the study. Feed and protein utilization, but not energy utilization, were enhanced significantly in T fish relative to NT-COM fish regardless of ration level. NT-W fish were not included in the two-way ANOVA of the performance results where genotype and ration level were the factors. Nevertheless, randomized block ANOVA of performance parameters for all treatment groups followed by Tukey's test with P = 0.05 indicated that NT-W-R W and NT-COM-R COM fish generally performed similarly. NT-W-R W, T-R W and T-R COM groups had lowest condition factors whereas those for NT-COM-R COM and NT-COM-R W were highest. Viscera-somatic indices were significantly enhanced in T fish relative to NT-COM fish (data analyzed by two-way ANOVA). Fish size-corrected terminal whole body proximate compositions were uninfluenced by treatment even though the initial moisture and lipid concentrations in T fish were respectively lower and higher than noted in NT fish. Fish mortality was uninfluenced by treatment. It is concluded that dramatic growth enhancement in T coho is mainly due to enhanced dietary intakes of protein and energy and to a small (∼ 17%) but nevertheless significant improvement in utilization of dietary protein for body protein synthesis. The latter occurred at high and reduced rations and may have been due to high and unregulated plasma growth hormone levels accompanied by increased titres of insulin-like growth factor (found elevated in this transgenic strain in other studies) and 3, 5, 3′ triiodo- l-thyronine. Collectively, these hormones likely directly stimulated tissue protein synthesis. Also, the former two hormones probably spared protein (amino acids) for growth by promoting fatty acid catabolism for energy. The latter effect, in turn, probably played a major role in appetite stimulation of T-R T fish while simultaneously protecting their tissues from excessive lipid deposition.