Evaluation of Substrate Type and Density as Factors in Optimizing Growth of Least Chub

Abstract

AbstractThe least chub Iotichthys phlegethontis is a diminutive and rare cyprinid endemic to the Bonneville Basin of Utah. As part of a species recovery effort, aquaculture techniques were investigated. Three experiments are summarized here: Two compared silt substrate and no substrate, and one evaluated the effect of three different densities on growth and survival. The substrate experiments were an attempt to compare extensive versus intensive culture. In the first test, growth of 4–7‐month‐old least chub in outdoor aquaria containing 2–3 cm of silt substrate was significantly higher than that of fish in indoor or outdoor aquaria with no substrate. Survival was unaffected by substrate treatment. In another test using fry that had just hatched, mortality rates were significantly higher in the aquaria treatment (mean ± SD = 95.3 ± 2.3%) than in the silt substrate treatment (45.3 ± 23.1%; P = 0.009). Final length was also significantly higher in the simulated ponds (mean ± SD = 10.2 ± 1.2 mm) than in the aquaria with no sediment (6.2 ± 2.7 mm; P < 0.001). In a final, 8‐week test, fish rearing densities of 2.27, 11.36, and 22.7 fish/L were compared among 5–6‐week‐old least chub. Growth and survival were not significantly affected within this range of rearing densities. These results indicate that extensive aquaculture using fertile fry ponds would produce more and faster‐growing least chub than intensive raceways or tanks, assuming predation and disease were not factors. High rearing densities are also possible with this schooling species of cyprinid.