NUTRITION AND BIOENERGETICS OF THE CHINESE HERBIVOROUS FISHES WITH IMPORTANT FOOD VALUES,Ⅱ.MAXIMUM CONSUMPTION AND DIGESTION OF SEVEN AQUATIC PLANTS BY CTENOPHARYNGODON IDELLA AND MEGALOBRAMA AMBLYCEPHALA

Chemical composition and energy contents were determined for seven aquatic plants which are natural foods of herbivorous fishes Under laboratory conditions(water temperature= 30℃;dissolved oxygen=8ppm;pH=7—8;light intensity=1800—2800Lx),measurements were made on the maximum rate of consumption and digestibilities of dry matter,protein, amino acids,fat,ash and carbohydrates in Ctenopharyngodon idella and Megalobrama amblycephala fed various aquatic plants.The size range was 8.70—22.02cm in length and 10.50— 226.56g in weight for C.idella,and 8.50—24.96cm in length and 6.50—381.05g in weight for M.amblycephala. 1.In the seven aquatic plants(Potamogeton crispus,Potamogeton maackianus,Myriophyllum spicatum,Vallisneria spiralis,Najas minor,Hydrilla verticillata and Spirodela polyrhiza), water content ranged from 80.85—92.72%,protein content ranged from 1.69—4.96%,fat content ranged from 0.35—1.09% ash content ranged from 0.98—2.45%,cellulose content ranged from 0.66—2.17%,and the content of non-nitrogen extracts ranged from 2.30—9.95%. The proteins of all the seven plants contained 17 common amino acids(tryptophane was not measured),including 9 essential amino acids for fish.The content of amino acids was highest in P.crispus(36.63mg/g wet wt.)and lowest in V.spiralis(12.92mg/g).Energy content was highest in P.crispus(3.36KJ/g wet wt.)and lowest in N.minor(1.28KJ/g). 2.Maximum rate of food consumption and digestibility in the two fish species fed each plant were related to the body weight(X,g)of the fish by the equation:Y=aXb,where Y (g/24hr or %)is either maximum rate of food consumption or digestibility.As body weight increased,the relative consumption rate decreased and digestibility increased.Usually,C.idella had higher rates of maximum food consumption,but lower digestibilities than M.amblycephala.