DeRyke and Scott 5 



next step in this analysis is to determine the life history of each of the forms 

 concerned in each food chain. 



By life history I mean the number of broods a form will produce, the 

 number of young in each brood, and the age at which the organisms begin to 

 reproduce. This is necessary in order that the turnover may be determined. 



An investment on which a 50 per cent dividend is declared once a 

 century is not so good as one which declares a 5 per cent dividend annually. 

 Nor is a $500 bond yielding 1 per cent as productive as a $100 bond yielding 

 6 per cent. So a small organism producing large broods at short intervals 

 may be a much more valuable member of a food chain than a large form 

 whose reproductive rate is slow. 



We have just determined that one of the little crustaceans known as 

 scuds (the amphiopod, Hyalella) contributes at a maximum approximately 

 100 pounds of fish food per acre during the growing months which may be 

 reckoned at seven months. We know that fish eat these but we do not know 

 how many one fish will eat or how many of these Crustacea it would take to 

 make a pound of fish. 



The fundamental reason why fish can be produced more cheaply than the 

 common land animals used for food is that much of the food eaten by mam- 

 mals and birds is used to keep up the temperature of the body. A young 

 bird must eat nearly its weight in food every twenty-four hours in order 

 to hold its own in weight. It is a matter of common knowledge that cattle 

 during severe weather scarcely hold their own in spite of careful feeding. 



Fishes use none of their energy to keep up their temperature. It all 

 goes for swimming or reproductive energy and for growth. This enables 

 them to go for rather long periods without food. In this latitude most of 

 our fish do not eat during the colder months. They may not lose much but 

 they certainly do not gain. During the warmer months they can feed but 

 it is probable that in most situations they eat their limit only occasionally. 

 Scant food supply and intermittent food supply are things that we must 

 attempt to remedy if we are to raise large fish in a short time. 



There is a direct relation between the amount of fish a given body of 

 water will produce and the amount of fish food it will produce. No cattle 

 raiser would think of putting 1,000 calves into a ten acre pasture lot. If 

 he did do this, at the end of two or three years he might have three to five 

 stunted cattle that had survived the terrible competition of the early months 

 of the feeding. 



Of course carniverous fish eat each other when there develops sufficient 

 difference in size, but independent of this factor, the reduction in fishes in 

 number or size or both to that which a lake or stream can support, is just 

 as certain as in the case of the calves cited above. 



May I illustrate the effect that plenty of food will have on the size of fish? 

 Probably there are as many bass in Florida that weigh 9 or 10 pounds as 

 there are in Indiana that weigh 5 or 6 pounds, but in Florida the bass can 

 eat 12 months in the year. 



Rainbow trout in Spencer Creek, Oregon, have never been known to 

 reach a length greater than 17 inches. These same trout when transplanted 

 to Diamond Lake reach a length of 40 inches and a weight of 27 pounds. 



The Division of Fish and Game of the Indiana Department of Conserva- 

 tion, under the very efficient management of Mr. George N. Mannfeld, in 1921 



