The measurements of filtering parameters under breathing and feeding of filter-feeding silver carp ( Hypophthalmichthys molitrix Val.)

Abstract

As a typical filter-feeding fish, breathing process of silver carp is combined with its feeding process when it filters plankton in water. The present experiments studied the relationships between breathing and feeding of silver carp in response to the reduction of dissolved oxygen (DO) levels. The results showed that (1) in the clean water without phytoplankton, normal DO levels (5.43–7.73 mg/L) did not affect significantly the respiration of silver carp in terms of respiratory frequency (f R), oxygen consumption rate (VO 2), respiratory stroke volume (V S.R), gill ventilation (V G) and oxygen extraction efficiency (EO 2); while DO level declined to 4.40 mg/L f R, V S.R and V G increased significantly and EO 2 decreases significantly; The VO 2 of silver carp reached the peak when DO levels declined to 2.21 mg/L; The critical oxygen level of silver carp was about 1 mg/L, at which the EO 2 of fish was substantially decreased to the lowest value. (2) f R, V S.R, V G and VO 2 of silver carp under feeding condition were significantly higher than those in clean water at oxygen levels ranging from 3.37 to 7.73 mg/L; While the EO 2 of the fish under feeding condition was lower significantly than that in clean water; V S.R, V G and V G/VO 2 of silver carp under feeding condition increased significantly when DO levels declined to 2.21 mg/L. In summary, silver carp fed actively and respired passively when DO levels were above 3 mg/L, i.e., it showed higher V G, higher FR and stable VO 2. While silver carp fed passively and respired actively when DO were below 3 mg/L, i.e., it showed sharply increased V G, decreased filtering efficiency (E) and anti-filtering response.