STANDING CROP OF THE MACROPHYTES OF LAKE TUNG-HU,WUCHANG,WITH REFERENCE TO THE PROBLEM OF ITS RATIONAL PISCICULTURAL UTILIZATION

The paper presents the results of investigations on the macrophytes of Lake Tung-Hu,Wuchang,carried out in the year 1962—1964.83 species,which constituted theaquatic vegetation,are listed.Data on biomass,based on sampling along 21 transects(involving 3 zones,17 plant-associations,and 224 sampling positions),are presented,and a comparison is made for the macrophytic biomass of 6 shallow lakes of theMiddle and the Lower Yangtze Basin.The monthly changes in biomass of 2 tran-sects (Ⅻ ⅩⅢ) have been followed up through the year.The biomass conditionsfor zones of different depth-ranges are analyzed.Lake Tung-Hu,28.5 km2 in area,had a peak average biomass of 1068.1 g (wetweight) or 94.8 g (air-day weight) or 82 g (oven-dry weight) or 322 kcal per squaremeter in August.Annual production of aquatic vegetation in the whole lake amo-unted to 30,440 metric tons in wet weight,or 2,337 t in oven-dry weight,or 9×109kcal in terms of calorific value.Potamogeton maáckianus ranked first in the pro-duction,being 38.2% of the total wet weight or 52.5% of the total air-dry weight,andit was followed by Najas major,Myriophyllum spicatum,Hydrilla verticillata and Ceratophyllum demersum in turn.In the lake,the annual primary production from aquatic macrophytes and phy-toplankton put together amounted to 25×109 kcal,of which the aquatic macrophytescontributed 36%.In passing,the authors discuss the problem of the rational utilization of this re-source in special regard to pisciculture,and a formula is proposed for calculating thestocking density of the phytophagous fish,for instance,Ctenopharyngodon:X=(B·P/K·W·S),in whichX——the number of fingerlings of the phytophagous fish to be stocked per mou (1mou=1/15 hectare)B——maximum average biomass (attained during August—October) of the macro-phytes suitable for fish consumption (in catties per mou) (1 catty=500 g)P——percentage of the macrophytic biomass intended to be consumed by the fishK——gross feed-coefficient of the phytophagous fish during the entire growing sea-son (in catties)W——expected average increase in weight per fish (in catties)S——percentage of the number of survivors (to the end of the growing season) tothe number of fingerlings stocked