Chapter XIV 



aiSmES OF THE POIID FISHF5 



Of the lower fish enemies to be found in the pond, several have already been 

 discussed in the introductory chapters on production biology: the predatorj'- water 

 insects and water insect larvae and the v;ater spider. All these animals are of 

 immediate danger only to brood and to very small fishes, but they are at the same time 

 very noteworthy food competitors. Their control and elimination in brood ponds, where 

 they cause the greatest injury, is brought about by the draining and liming of the 

 ponds during the tiine they are not in use and by water coverage immediately before 

 stocking them. *rhe only plants among the fish enemies, the bladderworts (Lentibular- 

 iaceae) are also prevented by these methods from occurring as pests in the brood pond. 



Counted among the higher fish enemies from the race of vertebrates which for the 

 most part directly devour fishes, are several amphibians and their larvae, various fish 

 devouring creeping animals, birds and mammals. Rats (water rats, brovm rats, mush rats) 

 need hardly be considered here, but they often are quite destructive to dams and other 

 pond structures. They are caught with wire baskets, small spring traps, or box traps, 

 or with strychnine and phosphorus (in meat bait), 



Anura, particularly the T/ater frongs and various toads rarely devour fish brood, 

 J-he predatoi-y activity of their larvae is insignificant, although all larvae become 

 injurious by eating up the food and cause extreme difficulty in fishing out carp and 

 trout brood ponds. The detriment is often very considerable, because of extremely 

 large larval swarms consisting of thousands of individuals. I have often seen many 

 barrels of tadpoles caught even out of small ponds. The addition of narrow mesh wire 

 fences around the brood extension ponds is expensive. The fences also do not keep out 

 frogs completely, but only moderate the damage. The catching of spawning frogs, re- 

 moving of the jelly-like spawn, netting out the swarms of larvae, baiting with meat 

 on fixed hooks and continuous netting out of accumulated larvae are methods of control 

 wliich are more or less worthy of reconmendation and more or less effective according 

 to local conditions. 



The larvae of salamanders and amphibian lizards and the tailed amphibians also 

 are brood robbers and competitors of the fishes for natural food. In contrast to frog 

 anuras these animals hardly have mass accumulations of larvae. 



Of all birds, the heron is justly the most feared in the carp pond fisherj''. In 

 many pond fisheries it causes yearly losses up to liO to 50 percent among the one-summer 

 carps and the smaller two-summer carps. I knov; of fisheries, where ^0 to 50 herons are 

 destroyed in almost every summer. 



The setting up of covered spring traps on elevations and of gun traps, the shooting 

 off, the destruction of the nests, and in amall ponds the stretching of wires serve for 

 control. The dv;arf reed bittern which causes considerable losses in brood and brood 

 extending ponds, is controlled by similar methods, liigratin:; fish eagles are frequently 

 observed in many localities in the act of catching carps. They can best be eliminated 

 by shooting them or by setting up spring traps on supports I, meters (13 ft.) high. 

 Perhaps at times the setting up of frightening -shot apparatus on supports, may be 

 sufficient, as y.'eigold has announced. 



There are almost always various species of diving birds on larger ponds, especially 

 the crested grebes, Dr/arf divers also establish themselves on small ponds. Shooting off, 

 and destruction of the nests are the best methods of destrojT-ng divers, lied neck divers, 

 eared grebes, and black neck divers are without greater significance. Gulls and similarly 

 crovfs and magpies like to devour sick fishes, whereby they very frequently become carriers 

 of worm cataract (see Chapter XV, K, 2) in trout fisheries. Poisoning them by fishes fill- 

 ed vd-th strychnine is said to work best. Furthermore the ice bird becomes quite destruc- 

 tive in trout ponds by catching little fishes I, to 1 centimeters (1.5 to 2,75 inches) 

 mostly Tfhile perched on overhanging branches or stakes. It is easiest caught in small 

 spring traps set on and chained to stakes, '.'fater ouzels can also be caught in the same 

 trap. They are rjire in North Germany hovrever. 



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