496 U. S. BUREAU OF FISHERIES 



In this case the bluegills serve as forage fish for the crappies, and 

 appear to be better suited for this purpose than either the golden 

 shiner or the blackhead minnow. The best production of black 

 crappie fingerlings was at the rate of 20,562 per acre. In addition 

 there were 1,430 exceptionally large bluegills, making the total pro- 

 duction of crappie and bluegills approximately 22,000 per acre. 



As regards weight, however, the best production was obtained in 

 a smaller pond, where the yield of black crappie and bluegill sun- 

 fish was at the rate of 260 pounds to the acre. This is the largest 

 yield of strictly game fish which has been obtained at Fairport. 

 In comparing these figures with the production at other hatcheries, 

 it should be remembered that no food was added to either pond other 

 than a small amount of fertilizer and that the output represents the 

 a.ctual amount of fish flesh produced in the pond. 



The results in both bass and crappie ponds indicate that a fairly 

 abundant growth of submerged vegetation is required for best pro- 

 duction. In all ponds showing a satisfactory yield of fish there was 

 a good growth of this type of vegetation, but ponds with scanty 

 vegetation or with a j^redominant growth of emergent plants were 

 less productive. 



Forage viinnows. — Observations on the blackliead minnow have 

 yielded some very interesting results. It was found that the activi- 

 ties of the male on the nest not only serve to protect the eggs from 

 various enemies but also to keep up a continuous circulation of water 

 and that the eggs soon die when the male is removed. This minnow 

 is very prolific and a single female may deposit several thousand 

 eggs during the season. One female under observation deposited 

 no less than 4,414 eggs. These eggs were not all deposited at once 

 but at 11 different times during the summer. A surprising result 

 was the discovery that young blackheads hatched early in the season 

 may mature and spawn when only 2 months old. 



Effects of high oxygen concentrations and changes in pH. — ^A 

 series of experiments have been conducted by Doctor Wiebe to 

 determine the effects on fish when the atmosphere above the surface 

 of the water is replaced with pure oxygen. The use of oxygen 

 instead of air when fish are to be shipped long distances is con- 

 stantly increasing, but the technique employed still leaves much to 

 be desired. Ordinarily the oxygen is forced into the water at the 

 bottom of the container and allowed to escape from the surface. 

 This, of course, results in a great waste of oxygen. It is also claimed 

 by some fish culturists that the gills are affected by the oxygen 

 and may become seriously inflamed. 



In view of these facts it was decided to try the effects of high 

 concentrations of dissolved oxygen by placing the fish in a closed 

 container and replacing part of the water with oxygen at various 

 pressures. Several species of fish were used in these experiments, 

 including large and smallmouth black bass, crappie, bluegill sun- 

 fish, goldfish, and golden shiners. It was found that all these fish 

 could tolerate an atmosphere of pure oxygen over the surface of the 

 water even when pressures as high as 10 to 15 pounds were main- 

 tained for a period of 24 hours. Dissolved oxygen concentrations as 

 high as 41 parts per million were obtained in these experiments with- 

 out injury to the fish. It was also found that sudden transfers from 



