The facilities at the Bozeman Center offer the opportunity to use Bridger Creek or spring water in the raceways. Chemical characteristics of the water supplies are similar. Alkalinity and total hardness (both in mg/L as CaCO3) and pH of the creek water were 189, 203 and 8.2, respectively (Russo and Thurston 1974); values for spring water were 181, 207 and 7.6 (analysis by Water Chemistry Laboratory, Montana State University, Bozeman, Montana).
Fish were anesthetized in a 1% salt solution containing 50 mg/l of MS 222 and then checked for ripeness. Ripe females were rinsed with fresh water and the eggs spawned into a strainer to drain off excess fluid. Eggs were then placed in a pan and fertilized. On each spawning day, nine to 18 females were spawned separately and fertilized with sperm from separate males. If additional females were spawned, eggs from three fish were pooled and fertilized with sperm from two males. Eggs were incubated in individual and pooled lots in Heath incubator trays supplied with spring water at the rate of 19 L/min (5 gal/min). Eggs were treated daily with formulin at a concentration of 1:600 for 15 min to control fungus. When eyed, eggs were counted with a Veeder-Root electronic counter. Dead eggs were picked out by hand with a suction bulb and glass tube.
Data collected for individual fish included female weight, total number of eggs per kilogram of body weight, and percent of eyes eggs (Figure 1). A comparison of two samples test (t-test) was used to statistically analyze the data (Snedecor and Cochran 1967).
Water Weight Fecundity Weight Eyed Source of ------------------------ per 1000 Eggs Female(kg) Eggs per Eggs per (g)a (%) female kg/female -------------------------------------------------------------------- Spring 1.99b 2992 1527 75 86 Creek 1.75 3094 1793a 72 86Figure 1. Statistics on egg production of rainbow trout broodstock held in spring water at 10_ C (50_ F) and Bridger Creek at lower temperatures.
a Data for all fished, pooled. b Value significantly higher (P < 0.05) than the other value in the same column.
A total of 39 females were spawned from the creek water and 66 females from the spring water. Gross observations such as "blood in eggs" or "some bad eggs" were made when spawn was taken. Fish observed with these conditions were not considered in the individual comparisons, because these eggs would normally be discarded. However, the data were included when overall egg weight per thousand eyed eggs was calculated (Figure 1).
Fish held in spring water were significantly larger at spawning time than those held in creek water; a difference directly related to increased food intake and higher metabolism at the higher water temperatures. Fish held in creek water produced more eggs per kilogram of body weight than did those in spring water, but the eggs were smaller; consequently, there was no significant difference in weight of eggs per kilogram of fish between groups. Neither was there a significant difference in total number of eggs per female or in percent eyed eggs between the fish held in spring water and those held in creek water (Figure 1).
Figure 2. Average temperature and ranges for creek versus spring water, beginning September 6,1977 (Week 1).
Figure 3. Number of rainbow trout held in spring water or creek water, spawned on different dates.
We also demonstrated that a domestic hatchery strain of fish that spawns in early winter in a hatchery environment can revert to typical spring spawning when exposed to temperatures experienced in the wild.
Combs, B.D., R.E. Burrows. 1957. Threshold temperatures for the normal development of chinook salmon eggs. Progressive Fish-Culturist 19:3-6.
Davis, H.S. 1953. Culture and disease of game fishes. University of California Press, Berkeley.
Hokanson, K.F.R., J.H. McCormick, B.R. Jones, and J.H. Tucker. 1973. Thermal requirements for maturation, spawning, and embryo survival of the brook trout, Salvelinus fontinalis. Journal of the Fisheries Research Board of Canada 30:975-984.
Leifritz, E., and R.C. Lewis. 1976. Trout and salmon culture (hatchery methods). California Department of Fish and Game, Fish Bulletin 164.
Russo, R.C., and R.V. Thurston. 1974. Water analysis of Bridger Creek (Gallatin County) Montana 1973. Montana State University, Fisheries Bioassay Laboratory, Technical Report 74-3, Bozeman.
Snedecor, G.W., and W.G. Cochran. 1967. Statistical methods. Iowa State University Press, Ames.
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