PRIMARY PRODUCTIVITY AND ENERGY CONVERSION EFFICIENCIES FOR SILVER CARP AND BIGHEAD CARP IN HIGH-OUTPUT FISH PONDS WITH THE BLACK CARP AS THE MAJOR SPECIES FOR CULTURE

The primary production by phytoplankton was determined during 1982—1984 for fish ponds with the black carp as the major species for culture. Investigations were made on the vertical and seasonal changes in primary p:oduction in relation to major ecological factors, overall fish yield and yields from the silver carp and big-head. During the growing season (April—November), the depth for photosynthetic compensation varied from 70—140 cm (mean:105cm) at 10:00 and from 90—160 cm(mean: 135cm) at 14:00 O2 production from the water column in the upper 1m accounted for over 90% of the total production. The mean daily O2 prodution ranged from 5.00—17.04mg O2m-2day-1 The daily gross oxygen production usually exceeded oxygen respiration. The annual oxygen production was 2063—2814g O2·m-2·year-1. Monthly primary production showed only one peak whilh usually occured in July -August. The relationship between primary productivity (Y, gO2·m-2·day-1) and solar radiation (X,Kcal·m-2·day-1) was: y=5.5509e1.2998×10-14X The relationship between primary productivity (Y,gO2·m-2·day-1) and temperature(X, ℃) was: Y=0.2527X+3.2078 The relationship between primary productivity (Y,gO2·m-2·day-1)and concentration of inorganic nitrogen (X, mg·1-1) was. Y=0.7650X+7.1650 The average phosphorus concentration was 0.01mg·1-1 and the N/P ratio ranged form 102—722, indicating that phosphorus was the limiting factor for primary production. The relationship between production (Y,gO2·m-2·day-1) and biomass (X, mg·1-1) in phytoplankton was: Y=11.5842e(-5.7850×10-3X Net phytoplankton production in wet weight was 100674.4, 118560, and 128197.6kg·ha-1·year-1 respectively in black carp ponds with net fish yields of 7500, 11250 and 15000 kg·ha-1·year-1 In ponds with both black carp and grass as carp the major species for cuture and with a yield of 1500 kg·ha-1 year-1, the net phytoplankton production in wet weight was 137323.2 kg·ha-1·year-1.Primary productivity (Y,gO2·m-2·day-1) increased with increased yield from silver carp and big-head(X,g fish m-2·day-1)in the form:Y=3.2599X+5.2568. During the growing season (April-November), the efficiency of converting solar radiation to gross primary production ranged from 0.81—1.11%. The efficiency of converting net phyto-plankton production to yield of silver carp and big-head ranged from 3.49—5.13% the ecological efficiency of converting solar radiation to fish yield was 0.028—0.055%.