Elevated Water Temperature, Crowding, and Food Deprivation Accelerate Fin Erosionin Juvenile Steelhead Trout. Developments in Fish Culture

摘要

The effects of water temperature, density as measured by density index (DI), andfood deprivation (alternating cycles of daily feeding and fasting) on dorsal fin erosion of steelhead trout Oncorhynchus mykiss through a six-month factorial experiment. Dorsal fin index (DFI) correlated inversely with age, length, and weight of fish and was significantly affectd by crowding (i.e., DI). Increasing DI also improved feed conversions and slightly depressed survival, but DI has no significant effects on weight gain, condition (K), or carcass composition. Water temperature (10 deg C or 15 deg C) had a strong significant effect on DFI, colder water improving DFI while slowing body growth. Low temperature treatments improved survival slightly and altered carcass composition by increasing moisture at the expense of fat and protein. The effects of density and temperature were also strongly interactive. Food deprivation slightly improved final DFI at low DI's, but greatly reduced the average size of fish affected by severe fin erosion. Food-deprived slightly fish exhibited carcass composition trends similar to fish reared in 10 deg C water. Feed conversion improved significantly with alternating fasting/feeding cycles. Histological evaluation proved inconclusive for physical fin nipping evidence or for the presence of detrimental microorganisms. We feed that incidental contact during schooling and/or vigorous feeding activity, although not documented, plays a key role in steelhead trout dorsal fin erosion.