EFFECTS OF SALINITY ON OXYGEN CONSUMPTION RATE AND AMMONIA EXCRETION RATE OF ALLOGYNOGEMETIC CRUCIAN CARP

Although people usually think that freshwater fish always live and be cultivated well in fresh water,actually,some kinds of freshwater fish also can survive even live better and grow faster in the waters which contain certain salinity than those in fresh water.As filial generation of Carassius auratus gibelio(female parent) and Cyprinus carpio singuonensis(male parent) by allogynogenesis,allogynogemetic crucian carp is regarded as a typical freshwater fish which grows rapidly in waters of less than 0.5‰ salinity.Because it grows faster than its female parent and tastes more delicious than its male parent,it is popular with people and has become an important breed cultivated in fresh water.In addition,it has advantages in adaptability and has been cultivated largely in ponds excavated on some soline-alkali soil or littoral.However,there are not any theories which can tell people what kinds of pond are suitable to cultivate allogynogemetic crucian carps efficiently and safely,and this leads to low benefits and high danger.In order to avoid these possible defects and guide people to cultivate allogynogemetic crucian carps in scientific way,the rules of the metabolic rate changes of allogynogemetic crucian carp were investigated when the salinity changed abruptly from freshwater to 1.5‰,3‰,6‰,9‰ and 12‰ respectively.Oxygen consumption rate was measured by the method of Winkler's iodometry,and ammonia excretion rate was determined with the sodium hypobromite oxidation method.The results showed that the oxygen consumption rate and ammonia excretion rate of allogynogemetic crucian carp increased with the rise of salinity.The level of oxygen consumption rate got to the peak at the 12h of the experiment,and then went down slowly.The oxygen consumption rate in salinity of 1.5‰ and 3‰ preserved lower level than the freshwater group at the 3d,but not distinctly(P0.05).However,the salinity of 6‰ and 9‰ groups came down after the 3d and retained higher stable level than the control group distinctly at the 10d and 15d(P0.05).The salinity of 12‰ group also came down after the 3d,but it kept at lower level than the control group,not distinctly at the 10d(P0.05).The ammonia excretion rate of all treatments reached the peak level at the 24h of the experiment.Only the ammonia excretion rate salinity of 1.5‰ changed not prominence(P0.05),the others rose notably(P0.05),and went down at the 10d.The ammonia excretion rate salinity of 3‰ remained at lower level than the control group but not distinctly(P0.05),and the salinity of 6‰,9‰ and 12‰ retained higher stable level than the control group distinctly(P0.05).Therefore,the results indicate that energy consumption and nitrogen metaboly of allogynogemetic crucian carp are the lowest when the salinity of water is 3‰,and it is likely to be the optimal salinity for allogynogemetic crucian carp.