PROGRESS IN BIOLOGICAL INQUIRIES, 1935 437 



natural waters. Our lack of information on these fundamental facts 

 is the greatest obstacle with which we now have to contend in 

 developing a scientific policy of fish management. Opportunities 

 for field investigations b}^ the Bureau of Fisheries have been greatly 

 extended through a recent cooperative agreement with the United 

 States Forest Service, which provides that waters in the national 

 forests may be utilized by the Bureau for experimental purposes. 



POND-FISH CULTURE 



Owing to lack of funds for construction of ponds at the Leetown 

 station, investigations in pond-fish culture during 1935 were again 

 limited to experiments conducted by O. Lloyd Meehean at the 

 j\ atchitoches (La.) station. These studies were a continuation of 

 those begun in 1934 which were designed to determine the relative 

 value of different fertilizers in pond culture. Although the ponds 

 fertilized v^ith cottonseed meal had produced, on the average, more 

 food than those in w^iich other fertilizers were used, the results of the 

 1934 experiments were not conclusive. For this reason a different 

 method was adopted in 1935. Instead of keeping the amount of 

 fertilizer per unit area constant, and varying its composition in each 

 pond as was done the previous year, the quantity of fertilizer was 

 varied, the composition kept constant, and the length of the fer- 

 tilizer period extended. In all cases cottonseed meal was used as a 

 fertilizer. 



It was found that the average weight of bottom organisms was 

 greatest in ponds that received the smaller amounts of fertilizer. 

 The data indicate that under conditions at Natchitoches a weekly 

 application of about 25 pounds of cottonseed meal per acre is 

 sufficient to maintain fertility. 



It was found that in general an increase in the production of bot- 

 tom organisms resulted in a corresponding increase in the production 

 of bass up to about 105 pounds of fish per acre. After this point 

 was reached further increase in bottom organisms had little effect 

 on the production of fish. 



Carbon and nitrogen determinations were made of the plants found 

 in the ponds. These studies showed that the ponds produced from 

 3.86 to 6.81 tons (dry weight) per acre of vegetation. Furthermore, 

 the equivalent of 189 to 282 pounds of nitrogen is tied up in the 

 vegetation in an acre of water during the season, in other words, 

 as much nitrogen as is found in 1.39 to 2.08 tons of 36 percent cot- 

 tonseed meal. These results indicate the extent of the loss in food 

 elements when large amounts of vegetation are removed from a pond 

 as is the common practice in pond culture. 



TROUT CULTURE 



Feeding expeiiments. — Feeding experiments at the Pittsford, Vt., 

 station during 1935 were confined to tests of a new food, sold under 

 the trade name of "Egg-Glo", which has been highly recommended 

 as a trout food by a number of fish culturists. It was found that 

 on a diet of 30 percent "Egg-Glo" and TO percent beef liver, rainbow 

 fingerlings made a considerably slower growth than a fish on either 

 a diet of 30 percent salmon Qgg meal and 70 percent beef liver, or a 



