hatchery at Bberswalde showed that the addition of about 20 to /^0 percent of natural food 

 to spleen caused rainbow trout brood to grow about 7.5 percent better, healthier, and 

 more resistant, than those Xn a parallel experiment which received cwily spleen. In 

 general, only water fleas (Cladoceme), copepodae and chironomus larvae are suited for 

 dispensing. All other water animals had to be disintegrated. This food is best grown 

 in small stagnating, sunny exposured fish-free ponds which are organically fertilized, 

 before or after filling with water, by distributing a wheelbarrow full of cow dung for 

 each 10 square meters of surface, or about 3 to 5 kilograms of meat flour or with liquid 

 manure, etc. At water temperatures below 10°C, of course, the growth has little success. 

 The food is fished out with fine nets, washed out, and distributed in small portions in 

 the brood apparatus during a temporary halt in the through current. There will be no 

 danger of carrying in disease producers if the ponds are really free of fish and have 

 been thoroughly disinfected before their first time use as a food pond. Cornelius, using 

 Daphnia on trout brood, determined a food quotient of 5.1 (13''C). With fingerlings he 

 found the following food quotients: --For flea crabs ( Gamma rus ) 3,9 at 9.2°C, for Chironomus 

 larvae A..U (9.3°C). 



I must also mention, that in the Agricultural Institute for Fishery in Berlin-Fried- 

 richshagen there were repeated occurrences of intestinal inflammations in trout fingerlings 

 (MLegel), whenever flea crabs and sewage water Chironomus larvae were given. Therefore 

 even the use of natural food is not an absolute protection against digestive disturbances, 

 as has been assumed up to now. 



E. The Giving of Food . 



1. Carp and Tench Feeding . 



An exclusive feeding of carps and tench is not possible in an economic way, as has 

 been fully explained in numerous places in this book. Carps and tench always require 

 for a good evaluation of the food, a simultaneous assimilation of at least 50 percent of 

 natural nutrition. The carp pond can not only be a "stall", it is always "stall" and 

 "pasture" in once. 



The individual growth of the fishes in general should be equally great with feeding 

 or without. Therefore in carp ponds in which feeding is to be done, more carps must be 

 set in, than when no feeding is done. In good ponds the number of stock can be doubled 

 without the feeding becoming unprofitable. The pond then contains 50 percent natural 

 supply, '50 percent food supply. Actually therefore 50 percent of the fishes, or better 

 said, 50 percent of each Individual carp should be grown by feeding. 



But this calculation also does not agree completely. By the doubling of the fish, 

 stock-density, of the number of eating mouths, the using up of the natural food supply 

 becomes greater. The non-eaten portion of food fauna of the pond becanes smaller. In 

 reality, therefore, over 50 percent of the nutrition is covered by natural nutrition. In 

 this lies the main advantage of the carp feeding. These actual conditions are not to be 

 overlooked in the individual case, and therefore, must be schematically calculated in 

 practice. To be noted is simply: — A first class pond which has a natural growth increase 

 of 300 kilograms per hectar (266 pounds per acre), can with profitable management achieve 

 a food increase of 300 kilograms, so that the total growth Increase amounts to 600 kilo- 

 grams. 



Since poorer ponds possess a lower natural growth increase, and a somewhat lower 

 piece growth (see table 17), the fish shock-density is much smaller, the utilization of 

 natural nutrition with natural stock much poorer, the non-eaten part of natural nutri- 

 tion is percentually much greater than in the first class pond. 



The consequence is, as first clearly expressed by Walter (1928), that in the poor 

 pond the total increase, with equally profitable feeding, grows more strongly in relation 

 to natural increase than in the case of the good pond. The "food increase" in a purely 

 mathematical sense is therefore relatively higher in the poorer pond than in the good 

 pond. The ratio of pure mathematical natural increase (natural stock) to mathematical 



144 



