抄録
Some fishes grow eating directly fresh water grass or phytoplankton. Transplanted grass carp, silver carp and tilapia are living in Japan. We can see natural propagation of the first two fishes in Tone river system and artificial production of their seedlings has been successful. Hera-crucian is also phytoplanktivoraus fish.
In the fishery field, aquaculture has been operated utiliging natural productivity of such water area and its basic technology has been developed.
Therefore, it is urgently required to establish a systematic organization of nutrient removal under the conditions as follows:
1) To release such fishes into eutrophicated water area under strict management for the purpose of predating water hyacinth or algal bloom.
2) To catch the all released fishes every year without fail and to use the harvest as the material of fish meal.
Feeding culture is the source of nutrients load for water area. Large amount of production and harvest of phytoplanktivorous fish which is equal to the double amount cultured fish is required for removal of excessive load by phytoplanktivorous fish.
However, when aquacultural production utilizes herbivorous fish living water area, much attention has to be payed to this point.
