Toxicity Of Ammonia Nitrogen On Uca Arcuata And The Effect Of Salinity On Its Survival And Food Intake

The ammonia nitrogen refers to the nitrogen forms of non-ionic ammonia （NH₃） and ionicnitrogen（NH₄⁺） that dissolved in water. The ammonia nitrogen has been one of the newpollutants to be controlled in Twelfth Five-Year Plan in China. The ammonia nitrogenwastewater is one of the important sources of eutrophication. High ammonia nitrogencontent showed toxic effects on aquatic animals and harmful to human health. Thelong-lived Uca arcuata often occupies relative stationary habitats, easily to be identified andcollected, and frequently exists in large population numbers, thus, is often used as abioindicator for pollutions. The effect of ammonia nitrogen and salinity on Uca arcuatawere studied in the present thesis. The main results are as follows:（1） Experiments were conducted to identify the effect of salinity on survivorship and foodintake of U. arcuata. Nine salinity gradients include0,5,10,15,20,25,30,35and40. Theresults showed that, with the gradual salinity changes, the survival rate of U. arcuata was100%in5days at salinity levels5-20. The crab could feed at salinity0-35, and the crab fedbest at salinity5^-10. With the acute salinity changes, the survival rate of U. arcuata was100%in5days at salinity levels5-20. The crab could feed at salinity0-30, and the crab fed best atsalinity5.（2） The acute toxic test of ammonia nitrogen on U. arcuata was studied under the condition ofpH8.09, temperature of28±1℃and salinity of5‰. The results showed that the96h medianlethal concentrations of ammonia nitrogen on U. arcuata at three growth stages （the carapacewidth less than1.5cm,1.5cm,1.5-2.5cm） were47.28,71.49and90.57mg·L^-1respectively,and differ significantly（P＜0.01）, the corresponding non-ionic ammonia （NH3） concentrationswere3.71,5.61and7.11mg·L^-1respectively. The safety concentrations were4.73,7.15and9.06mg·L^-1respectively, the corresponding non-ionic ammonia （NH3） concentrations were0.37,0.56and0.71mg·L^-1respectively. It turned out that there were significant positivecorrelation between the ammonia nitrogen concentration, intoxication time and toxicity. Thesequence of tolerance was the carapace width1.5-2.5cm＞1.5cm＞less than1.5cm.（3） To study the effects of ammonia nitrogen stress on immune ability of U. arcuata, groupsin different ammonia nitrogen concentrations (0,2.62,10.47,20.93mg·l^-1) and differentexposure times （1,3,9,18days） were set up in laboratory for comparison among the groups.The results showed that after1,9,18days treatment with ammonia nitrogen, THC in all thesethree treatments decreased significantly compared with those of the control （P＜0.05）.However, THC in all these three treatments showed the highest numbers on day3and increased very significantly compared with those of the control （P＜0.01）. Within short timefollowing the stress, superoxide dismutase （SOD） activity were stimulated in the lowconcentration of ammonia nitrogen while inhibited in the high concentration of ammonianitrogen. Progressive increase in malodiadehyde （MDA） level was observed with timeelapsed. Moreover, the augmentation of MDA changed with different concentration ofambient ammonia nitrogen that the higher concentration, the more augmentation of MDA.