In pond culture of common carp, live food is produced partly in the course of pond preparation before stocking, but most of the consumed natural food is produced together with the growing fish.
The technique of increasing the natural fish food production capacity of fish ponds is based on the use of manures, fertilizers and lime (Table 3.1, Table 3.2, Table 3.3, Table 3.4 and Table 3.5).
There are a wide range of different manures and fertilizers. Their usability depends on their actual contents and the quantity and frequency of their application (Table 3.1 and Table 3.4). Fresh manures are more effective than older dry ones. The quantities presented in Table 3.4 should be distributed in equal portions during the growing season. Smaller but more frequent doses are more effective than rarely distributed large portions.
Lime raises the pH of the water; most fish do best in water which has a pH between 7.0 and 8.5 (McLarney, 1984). Lime reduces the daily extreme fluctuation of pH, as well as supports useful chemical processes, such as decomposition and mineralization of organic materials (Ribianszky and Woynarovich, 1962; McLarney, 1984, Woynarovich, Moth-Poulsen and Péteri, 2010). Lime is important not only for supporting pond life, but also for disinfecting the pond bottom and controlling phytoplankton blooms.
There are two types of lime which are frequently used in pond-fish culture; powdered limestone or agricultural lime (calcium carbonate, CaCO3) and quicklime (calcium oxide, CaO). The first one acts slowly, while the second one is a strong form of lime which reacts not only quickly but also aggressively. Therefore, the disinfecting effect of quicklime at pond preparation or at the treatment of water is outstanding. The quantities of lime should be calculated based on Table 3.5. Within the indicated ranges, higher doses should be given from agricultural lime, and the smaller ones from quicklime. If there is about a seven to ten-day- long interval between the application of lime and manure/fertilizers, then the effect of both will increase (Woynarovich, Moth-Poulsen and Péteri, 2010).
Except for advanced fry rearing, the application of lime during the production season is also useful (Table 3.5).
As some of the essential nutrients are trapped in the mud of the pond bottom, in order to recycle these nutrients, as well as to aerate the mud, the bottom should be turned around. For this purpose, a harrow or a heavy, long chain dragged on the pond bottom should serve well. The use of a propeller near the pond bottom can also stir up and aerate the mud (Woynarovich, Moth-Poulsen and Péteri, 2010).
