ENEMIES OF THE FISH
To preserve the population of fish in fish farms and natural water bodies must constantly fight with their enemies and competitors. On reservoirs there are many species of animals that harm fish stocks. Some of them eat fish, others the same feed as the fish, still others are a source of pathogens of infectious diseases, etc. Among the enemies of the fish has a large group of mammals: shrew — shrew, muskrat, otter, mink, muskrat, water rat, and others that attack the fish. For example, mink and otter, living on the banks of large ponds, rivers, lakes and reservoirs feed primarily on fish, and their presence in the spawning grounds, as well as in the area of the hatcheries is highly desirable. Tangible harm can sadkovich in farms and hatcheries, especially in Malkovich farms, the water. She eats a fry and attacks the big fish, eating away their brain and eyes.
Water rat, muskrat, muskrat, whose life is closely associated with water, eat in a different food and fish. Muskrat destroys not only fish, but also, breaking through long burrows, often contributes to the erosion and destruction of earthen hydraulic structures (dams, dikes). This is especially dangerous for wintering ponds when unexpected or invisible water leak may die a large number of fish.
Includedirective the impact of these animals on the fish population in the conditions of pond fish culture is easy. They organize special traps, traps and other accessories; fur they sit in public procurement organizations. A large group of enemies are fish-eating birds: pelicans, cormorants, herons, gulls, loons and ducks, mergansers, river eagles, and others. the Most dangerous of them pelicans and cormorants. Feeding exclusively on fish, these large birds consume it in large quantities. So, each adult Pelican or cormorant may destroy the day (various sources) 2 — 4 kg of fish. Therefore, in areas of fish farming and mass spawning areas, the presence of these birds is undesirable.
Typically, they nest in dense thickets of reeds on the banks of ponds. Loons and grebes feed almost exclusively on fish. In those areas where they are distributed in large quantities, the damage to fisheries can be significant. Especially it is necessary to prevent settlement grebes near the nursery ponds, as they can cause significant damage to cultivated juveniles. The role of ducks in fish farms can be both negative and positive. In spawning and nursery ponds where they can feed on the juveniles, their presence is unacceptable, and in fattening ponds on the contrary, they benefit here: the ducks eat duckweed, hunt for weed fish, harmful insects, fertilize the pond with feces.
However, it is necessary to adjust the density and to prevent the accumulation of more than 200 ducks per 1 ha, as excessive pollution of the pond promotes the development of fish Gill rot and branchinecta, which leads to colonization of the fish dangerous to humans by pathogens from the group of Salmonella. Dangerous enemies of fishes are also considered river eagle, osprey and white-tailed eagle. They nest on the tops of large trees, the rocks, near large rivers and lakes, feed mainly on large fish, and each of these birds can destroy a large number of.
Attack fish and other birds (vultures, ravens, Harrier, kingfishers), especially when they lack basic food.
Great damage to fish stocks applied to some predatory reptiles amphibians and aquatic invertebrates. In spawning ponds are frogs, eating caviar, and notostracans, destroying fish larvae, hatched from eggs. Substantial damage to the livestock of fishes in ponds cause the snakes. In the study of 6 thousand stomachs of snakes, it was found that they ate more than 8 thousand kg of fish.
To reduce damage caused by birds, it is necessary to force them to leave their homes near water. In many fish farms in Europe and America used automatic carbide guns that the sounds of their shots to scare the birds from protected waters. To force the birds to move to other places can ruin their colonies, nests, clearing of vegetation of their habitats, the burning of dried riparian vegetation or other methods. In small ponds (trout, spawning, etc.) can protect the fish from attack of seagulls-setting over the pond rare grid. In larger ponds you can pull the wire.
To combat the herons over the pond pull two of a number of synthetic ropes at a height of 20 — 25 cm from the water or placed on the edges of the pond chain polyethylene floats at a distance of 30 cm from one another. Amphibians and reptiles are caught melkojacheistoj network and move into another (natural) pond. The notostracans destroyed by treating the pond hlorofosom or other methods.