FISHERY BULLETIN: VOL. 70, xNO. 1 



increasing salinity according to the schedules 

 outlined in Tables 1 and 2. 



Both groups of fish received the Oregon Moist 

 Pellet diet. The young salmon were fed five 

 times daily beginning 30 days after hatching. 

 After the fish had attained an average weight 

 of 1 g, the frequency of feeding was reduced to 

 three times daily. They were provided more 

 food than they would consume at each feeding. 



Fish were raised in 100-gal pl>^vood tanks 

 which were lined with fiber glass. Water was 

 introduced to each tank at the rate of one-half 

 gallon per min. Incoming fresh and salt water 

 were premixed in head tanks to obtain desired 

 salinities. Salinities were calculated from the 

 proportions of premixed seawater and fresh 

 water, and density of water in fish tanks was 

 measured periodically with hydrometers to in- 

 sure that salinities remained at their calculated 

 levels. 



The first experiment (Group I fish) began on 

 January 8 with newly hatched alevins. Group I 

 fish first received food on February 7, and se- 

 lected subgroups were exposed to water of 9 or 

 lT/(( salinity beginning on February 24. The 

 five subgroups were first weighed on February 

 27. The experiment ended on May 7. 



The second experiment (Group II fish) began 

 on February 16 with newly hatched alevins. 

 All six subgroups of fish were first exposed to 

 water of 5 or 9'/, salinity on March 6 while still 

 in the alevin stage, and they remained at these 

 salinities for 18 days. The fish were first fed 

 on March 18 and first weighed on April 7. The 

 experiment ended on May 6. 



Mortality of the 11 subgroups of fish during 

 the test periods ranged from to 6 /r of the orig- 

 inal number of fish placed in the tanks. Even 

 the maximum mortality {6^r ) was considered 

 to have no appreciable effect on the comparisons 

 of growth. 



The average wet weight of fish in each sub- 

 group was determined at 14-day intervals from 

 random samples of 30 fish. Excess water was 

 blotted from anesthetized fish before weighing. 

 Fish were weighed separately in a flask contain- 

 ing a known weight of water and were returned 

 to their respective tanks after each weighing. 



Table 1. — Exposure of Group I chinook salmon to water 

 of increasing salinity. Date of hatch — January 7, 1969. 



' Temperature of incoming water averaged 10.7° C for fresh water and 

 10.8° C for seawater. 



Table 2. — Exposure of Group II chinook salmon to water 

 of increasing salinity. Date of hatch — February 15, 1969. 



' Temperature of incoming water averaged 11.9° C for fresh water and 

 12.0° C for seawater. 



OBSERVATIONS ON GROWTH 



Growth rate was calculated for each subgroup 

 from the periodic measurements of wet weight. 

 Growth was assumed to be exponential over each 

 period considered, and a value for the daily in- 

 crement in body weight, which can be expressed 

 as a iiercent of body weight per day, was ob- 

 tained from the expression 



Wt 



(1 + h) 



(1) 



where Wt 



Wo 



h 



t 



weight at the end of the period, 



weight at the beginning of the 



period, 



the compounded daily increment 



of body weight, and 



days. 



It is convenient to solve equation (1) for 

 (1 + h) by converting the terms to common 

 logarithms and taking the antilog, i.e. 



log (1 + h) = log Wt 



log Wo 



(2) 



120 



