FEEDING INTENSITY OF SILVER CARP AND BIGHEAD UNDER NATURAL CONDITION(Ⅰ) FEEDING INTENSITY OF FINGERLINGS OF SILVER CARP AND BIGHEAD IN SUMMER

There has been a common understanding that feeding intensity of fishes varies with time so as to form a definite diel feeding rhythm, but whether there is such a rhythm in silver carp and bighead under natural condition is still lack of information. In the experiments of subyearling cultivation in coves and bays, the authors colleted 313 silver carp (6.8—12.8cm in body length and 4.78—33.95g in weight) and 217 bighead (4.6—11.7cm in body length and 1.92—27.98 g in weight) for the purpose of studying their diel feeding intensity.The index of fullness of fish intestine in relation to water temperature and dissolved oxygen in the natural environment was determined; the evacuation rate of fishes under experimental condition was determined as well. According to a modified Bajkov’s formula(D=C·24A/N), the estimates of the diel ration of both fishes were obtained.Results show that both silver carp and bighead have a feeding rhythm when living in natural condition. Generally, maximum feeding intensity appears in 16—19 o’clock and the minimum in 4—7 o’clock. The daily ration for silver carp was found to be 12.81—23.08% of the body weight; for bighead, 8.91—14.63% of the body weight. Of both fishes, dissolved oxygen has a positive influence on feeding intensity.