One-year-old rainbow trout Oncorhynchus mykiss were reared for 8 weeks at a density of either 56 or 267 g fish/L (based on the volume of net-pens), equivalent to density indexes of 2.3 and 11.1 g fish/L·cm total fish length), respectively. The fish were held in 0.6 x 0.3-m netpens submerged to a depth of 0.15 m. Two net-pens for each fish density were suspended in each of three 3, 040-L circular tanks provided with sufficient flow to maintain loading rates in the tanks at less than 800 g/(L·min). The fish were then subjected to an acute handling stress by being removed from the water for 60 s. No differences in the time course of changes in serum cortisol levels or hematocrits were observed over a 12-h period between fish in the two density groups. There were also no differences between the two groups of fish in weight, length, body condition factor (weight/length3), interrenal nuclear diameter, or the percentage of the anterior stomach that was mucosa. These results indicate that if high water quality is maintained, 1-year-old rainbow trout can be reared at a density index as high as 11.1 g/(L·cm) without impairing their growth or causing overt chronic stress.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Aquatic Animal Health|
|State||Published - Jan 1992|
Bibliographical noteFunding Information:
M. J. Kebus was sponsored by the Electric Pow-er Research Institute (grant 89-03). This research was supported in part by the University of Wis- consin-Madison School of Veterinary Medicine and College of Agricultural and Life Sciences; the University of Wisconsin Sea Grant College Pro- gram under the National Sea Grant College Pro-gram, National Oceanic and Atmospheric Ad- ministration, U.S. Department of Commerce; and the state of Wisconsin (federal grant NA90AA-D- SG469, projects R/AQ-18 and E/E-1). We thank Terence P. Barry, Thomas E. Kuczynski, Anita Lapp, Jim Held, Ra'anan Ariav, Pat Campbell, Bill Meier, John J. Magnuson, and Bruce A. Bar- ton for their assistance.