The Effects Of Ammonia And Ration Size On Growth And Toxicological Response Of Mullet, Liza Haematocheila

Mullet [Liza haematocheila（T. et S.）] is an important cultured species, the growthand physiological status during its early life stage are critical to the later culture. Inpresent paper, experimental ecological method was applied to study the effects of totalammonia （TAN） on the survival and food intake of mullet, the effects of ration size andammonia （TAN） exposure on the food conversion efficiency （FCE）, nitrogen excretion，growth，pepsin and glutamine synthetase（GS）in juvenile mullet was further studied.The results, described as follows, can provide the illustration of physical and ecologicalmechanism of ration size and ammonia exposure on growth and physiological status infish as well as the improvement of artificial rearing skill of mullet with theoreticalreference.（1） The acute toxicity of ammonia on juvenile mullet, Liza haematocheilaThe ammonia exposure had a significant impact on the survival of juvenile mullet,the relationship between the survival of juvenile mullet and ammonia was dose and timedependent. Conducted under water temperature18.5±0.5℃, salinity28, and pH7.8，the96h median lethal concentration (LC₅₀) and safety concentration （Sc） of juvenile mulletwere79.57mg·L^-1and7.96mg·L^-1, with the un-ionized ammonia （NH₃-N）1.74mg·L^-1,0.17mg·L^-1, respectively.（2）The effects of ration size and ammonia exposure on metabolic parameters andgrowth in juvenile mulletThe ammonia exposure had a negative effect on the food intake of juvenile mullet,with an inhibition rate of28.78%under high level ammonia. However, the food intakeof this group did not decrease with the prolonged experimental time, indicating anadaptation of juvenile mullet to ammonia exposure. Under the same ration size, the foodconversion efficiency （FCE, include FCEw and FCEe） of juvenile mullet decreased withthe increase of ammonia concentration; on the contrary, the ration size played a positiveeffect on the FCE of juvenile mullet under the same ammonia concentration. Only under high concentration could the ammonia inhibit the nitrogen excretion of juvenile mulletthat fed with the same level of food, the nitrogen excretion between control andlow-concentration group was not significant; due to the increase of exogenous nitrogenmetabolism, the growing ration size could increase the nitrogen excretion significantly.Growth was significantly influenced by ration size and ammonia exposure, as thecontrol and low-concentration group performed better than high-concentration group interms of special growth rate （SGR，include SGRw and SGRe） under the same ration size;meanwhile, the special growth rate （SGR） of juvenile mullet displayed even better withthe increase of ration size under each ammonia concentration. The difference in growthperformance is mainly attributed to variations in food intake and food conversionefficiency （FCE）.（3） The effects of ration size and ammonia exposure on two enzymes in juvenile mulletIn present study, the effect of ammonia exposure on the pepsin of juvenile mulletwas different from each ration size, only the pepsin activities of juvenile mullet fromhigh level feeding group was depressed by the high concentration of ammonia, showinga possible relation with food intake; the pepsin activities of juvenile mullet undercontrol and low-concentration were significantly impacted by ration size while underhigh concentration the influence was not significant. The food intake proves to be themain factor that influences the pepsin activity, and the high concentration ammonia mayinfluence the pepsin activity indirectly by inhibiting the food intake of juvenile mullet.The general trend of GS activities in gill and muscle of juvenile mullet was thesame. The GS activities of median and high-level feeding group was induced byammonia; the GS activities of control and low-concentration ammonia group displayeda significant increase with the rise in ration size, while in high-concentration group thedifference was not significant, indicating that ammonia is the main factor influencingGS activity in fish. Given the fact that GS has played a key role in ammoniadetoxification, moderate feeding can help to reduce the toxicity imposed by ammonia.