Effects of Feeding Regimens on the Proximate Composition and Condition Indices of Juvenile Koi Cyprinuscarpio Used as Forage

Abstract

Two comparative feeding trials examined the effects different feed regimens had on body condition indices, whole‐body proximate composition, and energy density of koi, a variant of Common Carp Cyprinus carpio, used as forage by the Texas Parks and Wildlife Department's hatchery program for piscivorous broodfish. Prior research indicated that feeding koi a high‐energy/protein diet for 2 weeks, then transitioning to a low‐energy/protein diet for the remainder of the production period was most cost effective without sacrificing biomass. However, previous analyses did not consider the nutritional content and energy density of the forage produced. Eight‐week trials were conducted in a recirculating aquaculture system (RAS) and at a production scale in plastic‐lined hatchery ponds to evaluate the effect of feeding regimens on the quality of forage produced (i.e., nutrient composition and total biomass) while measuring production costs. The RAS trial indicated that feeding regimen could significantly increase the nutrient composition, energy density, and production biomass of koi forage, particularly by transitioning from high‐energy/protein feed to a feed that compromises cost and energy/protein density. Koi in ponds grew to an appropriate size for use as broodfish forage under all feed regimens tested. Nutrient composition of fish did not differ significantly in the pond trial, indicating that natural productivity might compensate for some nutrient shortfalls of a feeding regimen. However, energy density of the forage was highest when fed high‐energy/protein feed. Cost of production was significantly higher when only feeding high‐energy/protein feed. However, this extra expense may be worthwhile in certain situations given the positive effects of more nutritious forage fish and higher gross forage production.