36 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



• CONTROL 



• HEATING CABLE & COVER 



• HEATING CABLE 



JAN FEB MAR APR MAY JLN JUL AUG 



Figure 9. — Production per female per month in the heated 

 tanks and in the control tank, and average minimum 

 and maximum water temperatures in the tanks. 



Analysis of the data indicates that although 

 some increase in spawning was induced during the 

 winter months by raising the water temperature, 

 the increase in production was not great. In ad- 

 dition, only a slight rise in water temperature ap- 

 parently produced the same results as a marked 

 increase in temperature. The results also indicate 

 that prolonged or constant high temperatures may 

 be detrimental to spawning. Innes (1951) 

 pointed out that at constant high temperatures 

 the oxygen content of the water becomes dimin- 

 ished and tiiis seems to have a weakening effect on 

 Hsh. Doudoroff (1957 : p. 415) stated— 



that persistent nonlethal deficiency of dissolved oxygen 

 undoubtedly can adversely influence the activities of 

 tishes and have serious detrimental effects on fish popula- 

 tions in their natural environments. 



The oxygen record (appendix table 4) discloses 

 that throughout the period of the experiment, tank 

 14 had generally lower concentrations of oxygen, 

 which may account for the decrease in fry pro- 

 duction during the summer months. 



Although tanks 13 and 15 had similar temper- 

 atures, fry production in these two tanks differed 

 significantly for the months of June to August. 

 While it is true that tank 15 was heated artificially 

 (thermostat set at 80° F.), much of the heat was 

 lost through convection. Thus, tank 15 remained 

 only slightly warmer than the control tank. The 

 average temperatures in both tanks fell within the 

 optimum temperature range for propagation, 

 which is from 20° to 35° C. (68° to 95° F.) ac- 

 cording to Chen (1953), while the weekly oxygen 

 determinations showed very little difference be- 

 tween the two tanks. We are unable to advance a 

 satisfactory explanation for the poor fry produc- 

 tion in tank 15. 



Table 8. — Summary: Fry production and temperatures of 

 brood tanks used in the heating experiment, January- 

 August, 1959 



[Temperature ° F.] 



Month 



Tank 13 (control) : 



January 



February 



March 



April 



May 



June 



July 



August -- 



Total 



Tank 14 (with heating 

 cable and cover) : 



January 



February 



March 



April 



May 



June... 



July.. 



August 



Number of fry 

 produced 



Total 



2.967 

 2,492 

 5,032 

 4.739 

 7.365 

 14, 456 

 19,319 

 5,010 



61,380 



4,064 

 4,448 

 5,922 

 992 

 4,804 

 4,935 

 2,376 

 



Total .--. 



Tank IS (with heating 

 cable): 



January 



February 



March 



April 



May 



June 



July -.- 



August 



Total. 



27,541 



3.046 

 4,424 

 11,166 

 4,660 

 7,269 

 4.905 

 1,555 

 822 



Per 

 female 



46.4 

 38.9 

 78.6 

 74.0 

 115.1 

 225.9 

 301.8 

 78.3 



63.5 

 69.5 

 92.5 

 15.5 

 76.1 

 77.1 

 37.1 

 0.0 



37, 847 



Average tem- 

 perature 



Mini- 

 mum 



71.4 

 67.9 

 70.6 

 72.1 

 73.5 

 75.0 

 77.0 

 77,3 



77.3 

 77.2 

 80.4 

 79.8 

 81.2 

 82.5 

 83.5 

 84.1 



47.6 

 69.1 



174.5 

 72.8 



113.6 

 76.6 

 24.3 

 12.8 



69,6 

 72.1 



73.6 

 74.8 

 75.7 

 77.3 

 77.9 



Maxi- 

 mum 



77.4 

 74.8 

 78.2 

 80.1 

 81.8 

 83.6 

 85.1 

 85.4 



81.4 

 81.8 

 85.9 

 85.2 

 87.2 

 88.6 

 89.4 

 89.5 



Temperature 

 range 



Mini- 

 mum 



63.0 

 64.2 

 67.7 

 67.1 

 70.1 

 72.6 

 74.3 

 72.3 



72.1 



74.8 

 78.0 

 76.0 

 76.8 

 81.0 

 79.0 

 79.8 



76.0 

 79.6 

 81.0 

 82.6 

 83.7 

 85.4 

 86.6 



Maxi- 

 mum 



83.4 

 78.5 

 81.9 

 84.6 

 86.4 

 86.2 

 90.4 

 90.3 



88.3 

 84.6 

 88.0 

 90.7 

 90.2 

 90.6 

 90.9 

 90.9 



65. 

 69.0 

 69.0 

 72.0 

 73.6 

 74.0 

 72.8 



78.0 

 83.0 

 85.0 

 87.0 

 85.4 

 89.9 

 89.4 



