Birge. — Plankton of the Lakes. "129 



start. So instead of getting picked off they grew up in great numbers and 

 became as big as they could. But they did not get food enough, and the 

 result is that they are decidedly smaller than the perch which are found 

 in lakes where there has been a natural depletion of the smaller fish from 

 year to year. I was told by the former Commissioner of Fisheries of 

 Pennsylvania that some of the men down there got hold of a small lake 

 back in the mountains, stocked it with bass, and did nothing with it for 

 some years. They thought they would go up there and see how the fish 

 had been getting along. There were large numbers of bass in the lake, but 

 while these had grown and were sexually mature, they were all small — I 

 think not over four inches long. I imagine that if a dozen big bass were 

 put in they would eat up many of these Bttle fellows with the result that 

 the fish would then be fewer, but larger. 



Mr. Titcomb : The suggestion about these larger fish reducing the 

 number of the smaller ones and perhaps changing the balance, is pertinent 

 to another point. It is generally thought that the introduction of new blood 

 in a lake does not improve the fish, that is, in a large, natural lake. I am 

 wondering whether your theories there account for a change in the growth 

 of fish in the waters I am going to mention, rather than the introduction 

 of new blood. In this instance it was pickerel, Esox reticulatus. One 

 pond stocked with fish never yielded anything over about twelve inches in 

 length. The sportsmen went to a lake a few miles distant where the 

 fish would run up to five pounds in weight, and imported some of these 

 larger fish. Two years in succession they introduced the larger fish into 

 this lake where the pickerel were of small growth and since then they 

 have been catching large fish in those waters. Is that probably due to the 

 fact that the large pickerel proceeded to restore the balance there and not 

 to the introduction of new blood? 



Dr. Birge : Yes, I think it is. You must bear this in mind : the supply 

 of food in any lake from all sources is strictly limited, and you are getting 

 at any given time, barring accidents, as much fish as the lake will raise — 

 unless you increase the amount of food. The food all comes back to 

 plankton material on the one hand and the shore material on the other. 

 Now, you have no means of increasing the supply of food, so far as I 

 know ; and the question you have to solve is, can you get a better utiliza- 

 tion? The question you raise would be a very interesting one to work out. 

 Can you find a minnow, for example, which will swim out into the open 

 water and eat this plankton more largely than it is now being eaten, and 

 also allow itself to be eaten by other fish? If you can do that, there is 

 no reason why j'ou should not short-circuit some of these losses and turn 

 them into useful flesh. I do not see that new blood of itself is going to 

 make any appreciable difference in the matter ; the fish in any lake are 

 going to grow as big as they can on the food that is available to them. 



Mr. M. D. Hart, Richmond, Va. : Would the selection of the best 

 species as practised by agriculturists not have a tendency, in your opinion, 

 to result in improvement so far as these various fishes are concerned? 



Dr. Birge : There is no question that work of that kind could be done, 



