Drainage channels
Drainage channels (drainage and irrigation), they are not stagnant waters in the literal sense, because their interconnections form a kind of network, resembling a river network. However, they are not exposed to contamination. They differ significantly from flowing waters, therefore we will consider them in the context of the group of stagnant waters.
When using the drainage channels for economic purposes, their specific conditions should be taken into account, separate from other waters. They are filled with groundwater, which is indeed poor in oxygen, but its other physical properties are very good (it is clean, has a more favorable temperature, etc.). In the canals, the properties of the water are still improving – the water becomes oxygenated, and also enriches with food washed out from the environment.
A common feature of most drainage channels is the tendency for water to heat up strongly and to overgrow with vegetation, both submerged, and coastal, the lushness of which beyond a certain degree is harmful. In extreme cases, its excessive development may deprive water of its economic value. Under these conditions, there is not enough living space for the fish themselves, as well as for the development of their natural food.
The fish stock of drainage channels should be as diverse as possible in terms of species, so that the individual components of the food are fully used. From bentophages (tj. fish that feed on benthos, that is, organisms associated with the substrate) carp are suitable for canals, tench and bream, Among predatory fish, pike is the perfect home, zander in larger hard-bottomed canals, and if there are potential hiding places in the sewer, also catfish. The companion fish may be roach, rudd, silver crucian carp, rosary, bleed, perch or single specimens of chub and ide. Even barbell and asp will stay in good flow channels.
The disadvantage of all the fish mentioned above is that they like to eat only animal organisms. Therefore, an irreplaceable role in economic activities is played by a group of herbivorous fish, including mainly grass carp and, to a certain degree, both species of silver carp. The importance of herbivorous fish in the fishing industry should be seen in their comprehensive and direct impact, tj. the use of vegetation (amur – thicker water plants, white carp – plant plankton) for your own development, as well as an indirect dependency, tj. due to the overall improvement of the environmental conditions.
