Effects Of Crowding Stress On Growth And Physiological Parameters Of Common Carp (Cyprinus Carpio L.)

Crowding stress usually occurs under the condition of high stocking density, which may cause turbulence in the physiological state of fish. Studying on the mechanism of crowding stress helps to master appropriate rearing density and provide reference for the establishment of healthy culture technology in intensive fish farming.This article dealt with the effects of acute and chronic crowding stress on physiological parameters of common carp (Cyprinus carpio L). The relationships among these parameters were also discussed.The results of acute crowding stress (stressed for 3h, the density is 70g/L) showed that just after the stress was relieved, the serum cortisol, glucose and lactate levels increased and were significantly higher than the control levels (P<0.05), while serum free fatty acid levels were significantly lower than the control values (P<0.05). After stress, cortisol levels descended and returned to control values in 24h. Glucose levels were still elevated and hitted the maximal values in 1h, then declined and returned to control values within 48h. Lactate levels were reduced and came to the minimal values at 4h, then returned to base values in 12h. While the free fatty acid rose to control values in 4h, then declined and remained lower than the basal levels after 24h. No change in either serum cholesterol or tryglicerides levels were found during the study (P>0.05).The results indicate that acute crowding stress caused changes of serum physiological parameters of carp. These changes were related to energy metabolism and might offset the increasing demand for energy during stress. However, these changes could return to control levels in a short time, which implied a kind of modulation mechanism existing in carp. So, acute crowding stress did not cause long-term effects on the physiological function of carp under such condition, and carp responded in a similar manner to other teleost species.The results of chronic crowding stress noted that after crowded for 28d, the serum urea nitrogen levels of carp in medial density groups (35g/L) were significantly higher than in the low density groups (also as control groups, 6g/L, P<0.01), while the activity of lysozyme were significantly lower than in the low ones. No significant differences werefound in other physiological parameters between these two groups (P>0.05). In high density groups, the serum cortisol levels were elevated compared to the low ones and had significant differences (PO.05), the serum glutamic-oxalacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), total protein, urea nitrogen, free fatty acid levels, feeding ratio (FR) and feed conversion ratio (FCR) were all significantly higher than in the low groups (P<0.01), while the specific growth rate (SGR), hepatosomatic index (HIS), especially the activity of lysozyme were significantly lower than in the low groups (P<0.05). Other physiological parameters were similar to the low ones (P>0.05).These results indicated chronic crowding stress had effects on the growth, feed consumption and some physiological parameters of carp, especially in the high density groups. In the high groups, crowding stress caused decline in growth, decrease in feed consumption, turbulence in metabolism, damage of liver and kidney, and decline in resistance to disease. Such high density is not suitable for carp culture. In the medial groups, only a small portion of the parameters were significantly different from the low groups. Fish in the medial groups did not experience a high-level state of chronic stress.