Density affects rearing performance of juvenile landlocked fall Chinook Salmon

Abstract

ObjectiveDensity‐related information for landlocked fall Chinook Salmon Oncorhynchus tshawytscha shortly after first feeding is poorly understood. This study was undertaken to determine the effects of a range of rearing densities (low, intermediate, and high) on rearing performance and survival of newly feed‐trained juvenile landlocked fall Chinook Salmon.MethodsThe fish were reared for 66 days in 1.8‐m (diameter) tanks with approximate volume of 2036 L at one of three loadings of approximately 2500, 5000, or 10,000 fish/tank.ResultThe initial and final densities for each of the three loadings were 0.73 and 8.93, 1.45 and 16.41, and 2.90 and 26.86 kg/m3, respectively. At the end of the study, the specific growth rates were significantly lower, total lengths were significantly shorter, and feed conversion ratios were significantly greater in the fish from the highest‐density treatment relative to the fish in the other treatments. Percentage of weight gain, final weights, and condition factor were significantly reduced in fish from the highest‐density treatment relative those at the lowest density. There were no significant differences in any growth metrics between fish that were reared at the lowest and intermediate densities. The intermediate density (5000 fish/tank) produced intermediate results that did not significantly differ from either the highest or lowest densities. Mortality was not significantly different among the density treatments.ConclusionAn initial loading of 5000 fish in 1.8‐m (diameter) circular tanks, corresponding to initial and final densities of 1.45 and 16.41 kg/m3, respectively, is recommended to minimize the detrimental effects of density on newly feeding Chinook Salmon while maximizing their production in often limited hatchery space.