Effects of Rearing Density upon Cutthroat Trout Hematology, Hatchery Performance, Fin Erosion, and General Health and Condition

Abstract Ahstract.—Cutthroat trout of the Bear Lake Bonneville strain, Oncorhynchus clarki utah, were used in two separate density experiments. In the first, fish were reared for 212 d in outdoor raceways at four densities; fish were allowed to grow into their final rearing density and were fed 7 d/week. Final rearing densities averaged 768, 1,597, 2,073, and 2,998 fish/m3, and corresponding density indices (DI = fish weight, Ib/[fish length, in ×water volume, ft3]) were 0,40, 0.90, 1.10, and 1,46. In experiment 2, crowding screens were adjusted monthly, and fish were fed 5 d/week: final rearing densities were 338, 739, and 1,634 fish/m3 (DIs of 0.19, 0.39, 0.75). Feed conversion and mortality did not significantly differ among densities for either experiment, Final mean weights did not differ among the four densities of experiment 1, but mean total length was significantly longer in fish reared at the lower densities. In experiment 2, final mean weight was significantly reduced in the highest density and...