The ordinate shows the actual total aquatic productivity in the pond. The influence 

 of the stock rate upon this productivity has not been consideredj we deal therefore with 

 like conditions all around. 



At a normal rate of stock (individual increase at least 600 grams) only a relatively 

 small portion of available aquatic organisms is consumed by fishes. Of this consumed 

 amount 2/3 are used for mere sustenance and l/3 for weight increase. 



The individual increase rate is high but sijnply for the reason that the easy and 

 slight e35)lo-'.tation of available aquatics only requires a minimum of effort. 



Loss and gain of energy during feeding are' in most favorable relations to each other 

 in the individual fish, and at a lov/er rate of stock, would be more favorable still. The 

 remnant of uneaten food animals, necessary for high individual grcnrth, is called the 

 "luxury requirement" by Tfalter. 



As the rate of stocks mounts, a continuously increasing portion of available aquatics 

 will be consumed. The reason for this lies in the fact that with increasing density of 

 population the feeding area of the individual fish becomes more and more restricted, thus 

 facilitating its detection of available aliments. 



But the rate of exploitation of the "aquatic pastures" does not rise in proportion 

 to the density of fish population. As this density increases — and with it "food detection", 

 for the above stated reasons — the opulence of available "aquatic game" decreases. Finally, 

 the hunt for food does not pay any longer, since the caloric value of the thinned out and 

 scanty food supply does not compensate for the loss in energy, expended in the hunt. At 

 a moderate rise in stock (four times above normal), conditions remain very favorable for 

 the total growth increase. They are even better than at a normal rate of stocking, since 

 the sustenance requirements of the individually smaller fish do not increase as rapidly as 

 thet ratio of consumed aquatics to unconsumed remains. 



At eight times the normal rate of stock, conditions become very unfavorable, and at 

 sixteen times above nonnal, almost all of the consumed amount of aquatics goes for mere 

 sustenance of the fish. There is practically nothing left to fhrther their increases, and 

 the individual increase slumps down to zero. At all events, it is worthy of note that in 

 ponds of the 3rd class yield stocked with carp of an average weight of 300 grams (1,650 

 fish per hectar) there is sufficient natural food to maintain the proper weight of fish. 

 This experience deserves consideration in wintering and artificial repression of fishes. 



A very important practical question is whether at any time-point of the year the 

 available supply of food animals (which could be determined by investigations of fishery 

 biologists), would allow a conclusion on the productivity of a pond in question. Nordquist 

 and others have disputed the possibility of that kind of "appraisal", but they have 

 probably gone too far. By considering the above-described quantitative variations of the 

 food animals, the customary methods of industrial practice, and the somewhat constant 

 individual growth of the various age classes, the amount of food animals found by fish 

 undoubtedly pennits sufficient conclusions on the trxie production of bottom animals and 

 thus on the yield, because under these conditions, the uneaten residue of the total food 

 animal production is much larger than the eaten portion. 



Lundbeck made observations on carp pon'^s, introducing what he termed the "normal" 

 F/B coefficient, i.e. the normal ration of v.ie yearly flesh production of fish (F) to the 

 average amount of aquatic bottom life (B). This coefficient is in Bemeuchen (a German 

 fishery) about 3, but varies between 1 to 6.5. According to my own findings, in 6 small 

 trout ponds, the coefficients amounted to 5.8 and 9.9 on the average during two years. 

 According to Lundbeck, the f/B Coefficient drops with rising individual growth, so the 

 correctness of pond operation is better determined by the individual growth. For ponds, 

 the F/b Coefficient is of no practical value. 



The absolute average quantities of aquatics per square meter are not very well known, 

 at present and vary no doubt according to the qualitative composition, l^om researches made 

 at Eberswalde and (by Lundbeck) in Bemeuchen, it was found that ponds of the II and III 

 production rate (100 kilograms per hectar) had an average of from 2.5 to 5 grams of 

 "exclusive food aquatics" per square meter, i.e. from 1,250 to 2,500 individuals at Ebers- 

 walde. 



l>-7»09 



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