The relationship of feed intake, growth, nutrient retention, and oxygen consumption to feed conversion ratio of farmed saltwater Chinook salmon (Oncorhynchus tshawytscha)

Abstract

Feed conversion ratio (FCR) is the ratio between feed intake and weight gain. By improving FCR within a species, feed intake can be reduced for the same amount of growth, thus reducing feed costs and environmental impacts. To enable selection for improved FCR, it is important to understand how FCR differs within a species and what factors might also be associated with FCR efficiency as potential drivers. This study identified high and low FCR phenotypes in farmed saltwater Chinook salmon (Oncorhynchus tshawytscha) and examined how the following physiological traits were correlated with FCR: daily feed intake (DFI), daily weight gain (DWG), protein, lipid and energy retention, and whole-animal metabolic oxygen consumption rates (including minimal and maximal metabolic rates and aerobic metabolic scope). High DWG and low DFI were strongly correlated with FCR efficiency and DWG and DFI were also correlated. FCR efficient fish also had higher retention of protein, lipid and energy and lower rates of minimal metabolism. Maximum metabolic rate and aerobic metabolic scope did not differ between FCR phenotypes. The results suggest that future breeding programmes selecting for feed efficient fish will likely also result in faster-growing fish that regulate their feed intake, retain a higher proportion of ingested nutrient, and have reduced maintenance costs, all of which are expected to reduce feed costs and environmental loading without impacting production.