Development of practical carp diets for reduction of total nitrogen loading on water environment.

Feeding experiments were conducted twice in practical culture scale to develop practical carp diets which are effective to reduce nitrogen excretion from carp without reduction of growth, feed effciency and increase of feed cost. For this purpose, the experimcntal diets were propared by using locally available low cost ingredients and fed to carp in net cages in Lake Kasumigaura. Results of two experiments suggested that dietary protein level could be reduced from 39% of the official standard for carp feeds in Japan to 30-35% by elevating energy level with carbo-hydrate such as wheat flour or with lipid such as beef tallow. The use of practical ingredients in these experiments resulted in reduction of feed cost. The most suitable protein and digestible energy levels in diets for carp cultured in Lake Kasumigaura to reduce N excretion are suggested to be about 35% and 350 kcal/100g diet. Total nitrogen excretion per ton of carp production was reduced by 22 to 36% of the value from commercial diets with CP above 39% by feeding these low protein-high energy diets.