THE RATIONAL DESIGN OF POND FISH CULTURE WITH REFERENCE TO THE PRINCIPLES OF YIELD INCREASE Ⅲ. COMPOSITION AND QUANTITY OF FOOD SUITABLE FOR THE GROWTH OF GRASS CARP

Grass carp fingerlings were fed in laboratory aquaria on different combinations of green feed (duckweed or Sorghum sudanense) and pelleted diets (17% protein in diet No. 1 and 25% protein in diet No. 2). Both the species of green feed and the type of pelleted diet affected the growth rate of the fish. Judged from growth rate, gross growth efficiency, protein efficiency ratio and other indices, the optimal proportion of green feed to pelleted diet was 20—50:1 when pelleted diet No. 1 was used, and 15—30: 1 when pelleted diet No. 2 was used. Pond experiments were conducted during 1987—1989, The proportions and quantities of green feeds and pelleted diets were adjusted on the basis of laboratory redults, the nutrient requirements by the grass carp in different growth stages and seasons, and the water quality requirement for the prevention of diseases. In the experimental ponds, the annual inputs of green feeds and pelleted diets were 11.25×104-12.00×104kg/ha and 11.25×103-12.00× 103kg/ha, respectively. The growth rate of the grass carp and the total weight gain by fish were 1.4 and 1.5 times, respectively, those in the control ponds using ordinary feeding regimes.