PROGRESS IN BIOLOGICAL INQUIRIES, 1935 439 



of feedstiiffs into live body '\vei<2;lit under the conditions of tliis ex- 

 periment, while the brown trout seemed to be least eflicient. 



Two lots of brook trout were fed separate diets in the experiments 

 to determine the most satisfactory amount of feed that will produce 

 the most economical gain in weight. One diet consisted of equal 

 parts, by weight, of beef liver and trimmed beef hearts; while the 

 other contained in addition to these meats dried skim milk, cotton- 

 seed meal, and whitefish meal. The results of these experiments 

 show clearly that (1) within certain ranges, the efficiency of feed 

 utilization is inversely proportional to the quantity fed; (2) the 

 utilization of dry feeds is much less efficient than that of raw meats, 

 although the dry feeds are more economical in cost; and (3) young 

 fry probably need 10 percent of their body weight in feed while 

 older trout, up to a length of 3 inches, need only about 5 percent. 

 Hatchery feed bills can be greatly reduced if a more effective method 

 of using dry feedstulfs can be discovered. 



Experiments were conducted to determine the amounts of calcium 

 and phosphorus in the trout body, and the source of these mineral 

 elements. There is good evidence to show that trout absorb calcium 

 from the water even as early as the egg stage. In the egg and the 

 sac fry stages phosphorus was found to be 6 to 8 times more abundant 

 than calcium. But during the subsequent period of rapid growtJi, 

 the calcium content of the body increases rapidly until finally in 

 older fish it tends to exceed the phosphorus content. 



Field 'hivestigatio7is. — To test the common belief that rainbow trout 

 W'ill not long remain in the smaller streams in which they have been 

 planted (at least in eastern streams), experimental plants of yearling 

 rainbow trout were made in the fall of 1933 and also in 1934 under 

 the direction of R. F. Lord. These plants were made in the Soutli 

 Branch of Cold River, a small mountain stream with an average 

 volume of 10 to 12 cubic feet per second. 



An attempt was then made to keep account of the number of fish 

 caught, by the following procedure: Anglers were provided with 

 blank forms on which they were requested to state the number of 

 fish they caught, as well as certain other information. These they 

 were asked to deposit in mail boxes set up for the purpose con- 

 veniently near connnon parking places. The mail boxes were painted 

 a brilliant red to attract attention, and advertised by conspicuous 

 signs which were posted along the stream calling attention to the fact 

 that the Bureau of Fisheries was attempting to secure data on the 

 number of fish taken annually from the stream as a guide for future 

 stocking. 



As recorded in a previous report, the results for a similar experi- 

 ment in 1934 were unsatisfactory, only 87 fish being reported out of 

 TOO fish planted the previous fall. This Nvas a return of approxi- 

 mately 12 percent, but it is probable that only a small proportion 

 of the anglers reported, and that the actual total catch of planted 

 fish was much greater than that figure. 



In the fall of 1934, 1,000 yearling rainbows were planted in the 

 same stream. These fish were marked by removing the right pelvic 

 fin to distinguish them from the fish planted a year previously, which 

 had the left pelvic fin removed. The fish were well distributed along 

 the stream, every effort being made to avoid too great a concentra- 

 tion in any area. 



