In a pre-experiment test, 60-g trout were grad- 

 ually adapted from fresh water to 30%o salinity 

 within a 1-day period with a mortality of 5%. 



These results indicate that a gradual change 

 from to 30^f salinity over a 10-day period can 

 be accomplished with low mortality. Since other 

 studies have indicated that larger fish are more 

 easily adapted to higher salinities than smaller 

 fish (Awakura, 1962; Sato, 1965), this conclu- 

 sion only holds for the 60-g fish. 



Growth, survival, and food conversion data 



Growth curves for the three experimental 

 groups are shown in Figure 2 along with the 

 average water temperatures for the correspond- 

 ing period. During the first 5 weeks of this 

 experiment when the growth rates of all groups 

 were similar, temperature differences were not 

 as large. Once temperature differences occurred, 

 growth rates were affected. The final average 

 individual weights (256 g) were significantly 

 higher (P < 0.05) in the freshwater groups 

 which were maintained at near constant tem- 

 perature (averaging 21.3°C) than in the colder 

 saltwater (13.5°C) groups (217 gin the low den- 

 sity group and 176 g in the high density group) . 

 The average final density (Table 1) was sig- 

 nificantly greater (P < 0.05) from the highest 

 stocking density tanks in brackish water (Group 

 2) than from the lower density brackish water 

 (Group 1) and freshwater (Group 3) tanks. 



Food effiiciency and survival were best in the 

 lower stocking density brackish water tanks 

 (Group 1) and poorest in the freshwater tanks 

 (Group 3). A gradual mortality of one or two 

 fish daily was observed in the freshwater group 



It 



It 

 Uj 

 Q. 



Uj 



25 . 



20 



15 



10 



X 



v> 

 uj 



Uj 



t 

 (t 



250 



200 



150 



100 



50 



9 

 WEEKS 



13 



16 



Figure 2. — Water temperatures and growth curves from 

 an experiment in which rainbow trout were reared in 

 fresh and brackish waters. The solid and broken lines 

 represent temperatures for the freshwater and brackish 

 water groups, respectively. The triangles represent 

 average weights of the fish in the freshwater group, and 

 the circles and squares represent average weights for 

 the low and high density brackish water groups, re- 

 spectively. 



which was maintained at temperatures in excess 

 of the optimum temperature for rainbow trout. 

 Temperature had a greater effect on growth, 

 food conversion, and survival than did salinity. 

 The freshwater group maintained at approxi- 

 mately 21°C grew faster than the brackish water 

 group on the individual weight basis, but had 



Table 1. — Experimental data from the entire 16-week growing period 

 (December 4, 1970-March 26, 1971). 



1 Brackish wafer (incoming) was pumped from Skidaway River which varied In temperature while fresh water 

 was direct from a well and a^ a constant temperature (22°C). 



2 Values follow by the same letter are not statistically differenli {P > 0.05). 

 ' Food conversion ratio (grams feed/gram gain). 



1294 



