The Relationships Bbetween Breathing And Feeding And Their Regulatory Mechanism In Silver Carp Hypophthalmichthys Molitrix Val. And Grass Carp Ctenopharyngodon Idellus

1 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), respiratory stroke volume (V_S.R), gill ventilation (V_G) and oxygen extraction efficiency (EO₂) (P>0.05); while DO level declined to 4.40 mg/L f_R, V_S.R and V_G increased significantly and EO₂ decrease significantly (P<0.05); The oxygen consumption rate (VO₂) of silver carp reached the peak when DO levels declined to 2.21 mg/L; The critical oxygen level of silver carp was about 1mg/L, at which the EO₂ of fish was substantially decreased to the lowest value. (2) f_R, V_S.R, V_G and VO₂ 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 (P<0.05); While the EO₂ of the fish under feeding condition was lower significantly than that in clean water (P<0.05); V_S.R, V_G and V_G/VO₂ of silver carp under feeding condition increased significantly when DO levels declined to 2.21 mg/L (P<0.05). 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 VO₂. While silver carp fed passively and respired actively when DO were below 3 mg/L, i.e., it showed sharply increased V_S.R, decreased filtering efficiency (E) and anti-filtering response. 2 The present experiments studied the parameters of breathing and feeding of silver carp in response to the reduction of algae biomasses levels. The results showed that (1) the respiratory frequency (f_R), gill ventilation (V_G) and V_G/VO₂ of silver carp did not show significant difference among algae biomasses of 0-23.77 mg/L (P>0.05); while algae biomasses increased to 63.28 mg/L f_R, V_G and V_G/VO₂ of silver carp increased significantly and reached the peak, and declined significantly with more increases of algae biomasses (P<0.05). The oxygen consumption rate (VO₂) of silver carp increased significantly with increases of algae biomasses (P<0.05), but there are no significant differences in VO₂ among 63.28-242.05 mg/L of algae biomasses (P>0.05). With increases of algae biomasses, the oxygen extraction efficiency (EO₂) of silver carp declined, then increased and reached the peak when algae biomasses increased to 242.05 mg/L. There are no significant differences in respiratory stroke volume (V_S.R) among 63.28-242.05 mg/L of algae biomasses (P>0.05). (2) Filtration rate (FR) of silver carp increased significantly with increases of algae biomasses, but did not show significant differences among 63.28-242.05 mg/L of algae biomasses (P>0.05). The clearance rate (CR) and filtering efficiency (E) of the fish showed the same curve with the EO₂ during increases of algae biomasses, and reached the highest value while algae biomasses increased to 242.05 mg/L (P<0.05). Moreover, the fish appeared the anti-filtering response at algae biomasses of 137.86 mg/L and 242.05 mg/L.3 The present experiments studied the parameters of breathing and feeding of silver carp in response to the reduction of dissolved oxygen (DO) levels when the fish fed Padorina morum (diameter 20.1±4.6μm) and Chlorella ellipsoidea (diameter 6.8±1.3μm), respectively. The results showed that (1) respiratory frequency (f_R) and oxygen consumption rate (VO₂) of silver carp did not show significant differences when the fish fed Padorina morum or Chlorella ellipsoidea at DO levels of 0.98-7.49 mg/L (P>0.05), and the f_R of silver carp in Chlorella ellipsoidea group was higher significantly than that in Padorina morum group at DO levels of 0.98-7.49 mg/L (P<0.05); Normal DO levels (5.16-7.49 mg/L) did not affect significantly the respiratory stroke volume (V_S.R), gill ventilation (V_G) and V_G/VO₂ of silver carp in two groups (P>0.05), but the V_S.R, V_G and V_G/VO₂ of fish in two groups began to increase sharply while DO levels declined to below 4.04 mg/L (P<0.05); The oxygen extraction efficiency (EO₂) of silver carp in two groups increased significantly with decline of DO levels from 7.49 mg/L to 0.98 mg/L; V_S.R, V_G, EO₂ and V_G/VO₂ of silver carp in two groups showed the same trend at DO levels of 0.98-7.49 mg/L (P>0.05). (2) There are no significant differences in the filtration rate (FR) and filtering efficiency (E) of silver carp in two groups at normal DO levels of 5.16-7.49 mg/L (P>0.05), but the FR and E of fish in Padorina morum group were higher 4 times and 6 times than these in Chlorella ellipsoidea group, respectively; The FR and E of fish in two groups began to decrease significantly while DO levels declined to below 4.04 mg/L (P<0.05); The clearance rate (CR) of fish in two groups did not show significant differences while DO levels declined from 7.49 mg/L to 3.09 mg/L (P>0.05), but the CR of fish decreased significantly with the more decline of DO (P<0.05) in two groups; The CR of fish in Padorina morum group were higher 6 times than these in Chlorella ellipsoidea group at DO levels of 0.98-7.49 mg/L (P<0.05).4 The present experiments studied the parameters of breathing and feeding of starved and un-starved silver carp in response to the reduction of dissolved oxygen (DO) levels when the fish fed Chlorella ellipsoidea. The results showed that (1) respiratory frequency (f_R) and oxygen consumption rate (VO₂) of starved fish did not show significant differences among DO levels of 0.89-7.43 mg/L (P>0.05); normal DO levels (5.28-7.43 mg/L) did not affect significantly the respiratory stroke volume (V_S.R), gill ventilation (V_G), V_G/VO₂, filtration rate (FR) and filtering efficiency (E) of starved fish (P>0.05), but the V_S.R, V_G and V_G/VO₂ of starved fish began to increase significantly and the FR and E of starved fish began to decrease significantly while DO levels declined to 4.14 mg/L (P<0.05); There are no significant differences in the clearance rate (CR) of starved fish among DO levels of 3.17-7.43 mg/L (P>0.05), but the CR of starved fish began to decrease significantly while DO levels declined to below 3.17 mg/L (P<0.05); The oxygen extraction efficiency (EO₂) of starved fish increased significantly with decline of DO levels from 7.43 mg/L to 0.89 mg/L. (2) Normal DO levels (5.28-7.43 mg/L) did not affect significantly the f_R, VO₂, V_S.R, V_G and V_G/VO₂ of non-starved fish (P>0.05), but these parameters began to increase significantly while DO levels declined to 3.17 mg/L (P<0.05); With the decline of DO levels, EO₂, FR and CR of non-starved fish increased, and reached the peak at DO level of 3.17 mg/L, then these parameters began to decrease while DO levels decline to 1.90 mg/L, but the E of non-starved fish decreased significantly when DO levels declined from 7.43 mg/L to 0.89 mg/L. (3) The f_R, VO₂, V_G, V_G/VO₂, FR and CR of starved fish were significantly higher than those in non-starved fish at DO levels ranging from 4.14 to 7.43 mg/L (P<0.05), while the EO₂ and E of the fish under starved condition were lower significantly than those in non-starved condition DO levels of 3.17-7.43 mg/L and 5.28-7.43 mg/L, respectively (P<0.05).5 Respiratory parameters of grass carp were studied in conditions of temperature changes, 30°C-25°C-20°C-15°C-10°C-15°C-20°C-25°C-30°C (Group I) and 10°C- 15°C-20°C-25°C-30°C-25°C-20°C-15°C-10°C (Group II). The results showed that the respiratory frequency (f_R), oxygen consumption rate (VO₂), respiratory stroke volume (V_S.R), gill ventilation (V_G) and water convection requirement (V_G/VO₂ ) of grass carp in Group I decreased 5.4, 5.8, 1.6, 10.3 and 1.7 times while temperature changed from 30°C to 10°C, respectively. While recovering from 10°C to 30°C, the V_S.R and V_G/VO₂ of the fish went back to the initial levels, but the f_R, VO₂ and V_G of the fish presented significantly higher values than their initial ones (P<0.05). In Group II, the f_R, VO₂, V_S.R, V_G and V_G/VO₂ of the fish increased by 3.9, 5.8, 3.0, 11.3 and 1.9 times while temperature rose from 10°C to 30°C, respectively, and all of these parameters decreased to the initial levels while temperature returning to 10°C. The oxygen extraction efficiency (EO₂) of grass carp remained almost constant in both Group I and Group II during temperature changes between 10°C and 30°C. In addition, the f_R, VO₂, V_G and EO₂ of the fish in Group II were significantly higher than those in Group I at 15°C, 20°C, 25°C and 30°C (P<0.05), but the V_S.R in Group II were significant lower than those in Group I at 10°C, 15°C and 30°C (P<0.05). The V_G/VO₂ in two groups showed there were no significant differences in the V_G/VO₂ between Group I and Group II at 15°C, 20°C, 25°C and 30°C (P>0.05). The Q₁₀ values for f_R, VO₂ and V_G in grass carp were 1.75-2.47, 2.39-2.64 and 3.21-3.48 at 10-30°C of temperature interval, respectively. Grass carp showed partial metabolic compensation to temperature. These results indicate an ecological advantage for this migratory species. The study results also suggest that grass carp has shown good suitability for aquaculture due to its regulatory ability to acute temperature changes.6 Respiratory parameters of grass carp were studied during dissolved oxygen (DO) changes form normal DO to hypoxia, then return to normal DO at 15°C, 25°C and 30°C acclimation, respectively. The results showed that the respiratory frequency (f_R), oxygen consumption rate (VO₂), respiratory stroke volume (V_S.R), gill ventilation (V_G) and water convection requirement (V_G/VO₂ ) of grass carp increased with raised acclimated temperature, but the oxygen extraction efficiency (EO₂) of grass carp deceased with raised acclimated temperature. The f_R, VO₂, V_S.R, V_G and V_G/VO₂ of fish increased significantly with decline of DO levels at 15°C, 25°C and 30°C acclimation (P<0.05), but the VO₂ of fish began to decrease significantly while DO declined to critical levels (P<0.05). The EO₂ of grass carp remained almost constant above critical DO levels, and began to decrease significantly below critical DO levels (P<0.05). The f_R, V_S.R, V_G and V_G/VO₂ of grass carp deceased sharply after 0.5 h of return to normal DO levels from hypoxia at 15°C, 25°C and 30°C acclimation (P<0.05), but these values were higher than their initial values. And the VO₂ and EO₂ of fish increased sharply after 0.5 h of return to normal DO levels from hypoxia at these acclimated temperature (P<0.05); The breathing parameters of grass carp were gradually closed to their initial values when the time returned to normal DO was prolonged at 15°C, 25°C and 30°C acclimation; These breathing parameters of fish reached their initial values in 2.5 h returned to normal DO at 25°C and 30°C acclimation. The critical DO levels of grass carp were 2.45 mg/L (34.1 mmHg), 2.36 mg/L (40.0 mmHg) and 2.35 mg/L (43.6 mmHg) at 15°C, 25°C and 30°C acclimation, respectively.7 The relationships between oxygen availability and metabolic cost of breathing in grass carp were studied in response to the reduction of dissolved oxygen (DO) at 15°C, 25°C and 30°C. The results showed that the respiratory frequency (fR), respiratory stroke volume (V_S.R), gill ventilation (VG) and VG/VO₂ of grass carp increased significantly with decline of DO levels at 15°C, 25°C and 30°C (P<0.05); Increasing of VG in grass carp resulted from both increasing of fR and V_S.R; The oxygen extraction efficiency (EO₂) of grass carp kept stable during increasing of VG with decline of DO levels. The metabolic costs of breathing of grass carp were 17.13 %, 19.62 % and 20.22 % of total oxygen consumption rate (VO₂) at normal DO levels of 9.35 mg/L (15°C ), 6.26 mg/L (25°C) and 5.79 mg/L (30°C), respectively; With decline of DO levels, the metabolic costs of breathing of fish increased gradually, and reached 71.60 %, 54.57 % and 60.57 % of total VO₂ at DO levels of 3.09 mg/L (15°C ), 2.91 mg/L (25°C) and 2.54 mg/L (30°C) , respectively. The results suggest that grass carp should not be exposed to long periods of low DO since portions of the metabolic energy costs are used by the ventilatory system were high, as would be affect its growth and breeding.