A Survey of Trout Fin Erosion, Water Quality, and Rearing Conditions at State Fish Hatcheries in Utah

Abstract

A total of 600 hatchery trout were examined for signs of fin erosion including rainbow trout Oncorhynchus mykiss, cutthroat trout O. clarki, brook trout Salvelinus fontinalis and brown trout Salmo trutta. A scoring system was used to evaluate erosion on all fins from 20 fish samples. Water quality and hatchery rearing variables were also determined for corresponding raceways or ponds. For rainbow trout groups (N= 24), stepwise multiple linear regression was used to interpret the relationship between fin erosion and the other variables. These fish groups averaged between 92 and 243 mm in total length and no significant correlation was observed between length and a fin erosion index (r = 0.045). The best‐fit regression model (adjusted R2= 0.689) suggested that fin erosion was correlated with lower alkalinities, unnatural bottom substrates (concrete or steel), higher unionized ammonia levels, and higher fish densities. Despite significant variation between hatcheries, fin condition was significantly better in rainbow trout than in cutthroat trout in three of four hatcheries containing both species and the same substrate. Fin erosion in rainbow trout occurred primarily on dorsal fins, followed in order of decreasing severity, by pectoral, caudal, anal, and ventral fins.

Fin condition and growth among rainbow trout reared at different sizes, densities and feeding frequencies in high-temperature re-circulated water

“…Erosion of the dorsal fin and, secondarily, the pectoral fins (Bosakowski and Wagner 1994), has previously been highlighted when rearing environments are inappropriate or fish are aggressive to each other (Bosakowski and Wagner 1994;Moutou et al 1998;Winfree et al 1998). Caudal, pelvic and anal fins were only affected to a minor degree during the experiments, while the adipose fins were largely unaffected.…”

The relationships between stocking density and welfare in farmed rainbow trout

“…Of the seven studies in which fin damage was assessed, the majority found an adverse effect of density (Table II). In a survey of commercial hatcheries, Bosakowski & Wagner (1994b) also found that fin damage was correlated to density amongst other factors. An effect of density is affirmed by the observation that fin condition improves after the density of the fish is decreased (Purser & Hart, 1991).…”

“…Reduced food conversion efficiency and growth rate are also documented effects of decreasing DO (Brett, 1979). Bosakowski & Wagner (1994b) correlated UIA levels with increasing fin erosion. Soderberg et al (1983) correlated mortality with ammonia levels and suggested that exposure to ammonia predisposed the fish to infection by ectoparasitic protozoans.…”

“…Although fin damage in salmonids has been examined in numerous studies, and is a well documented effect of increasing density (e.g. Bosakowski & Wagner, 1994b;Miller et al, 1995), the actual causes and the possible role of aggressive nipping is unclear.…”

“…aggressive nipping or abrasion (with conspecifics or the walls of the rearing system), or poor handling. Further erosion may then result from continued physical processes and/or additional environmental factors such as water quality (ammonia and alkalinity), sunlight, and pathogen infection (Kindschi, 1987;Kindschi et al, 1991c;Bosakowski & Wagner, 1994b). Density can theoretically promote the initial cause as well as the secondary infection-due to deterioration in water quality and increased potential for pathogen transmission.…”