Effects of chronic ammonia nitrogen toxicity on the gill tissues and non-specific immune indexes of juvenile Crucian auratus
This experiment was conducted to investigate the acute toxic effects of ammonia nitrogen on juvenile Carassius auratus and its impact on the gill tissue structure and non-specific immune indices.Healthy juvenile cru-cians were randomly divided into seven groups,which were fed in the water environment with the mass concen-tration of NH4C1 ranging from 160 mg/L to 720 mg/L for acute toxicity test.The 96 h LC50 and SC were ob-tained and the chronic toxicity test was carried out based on the previous results.The concentrations of NH4C1 were 0,6,15 and 24 mg/L,respectively,and the experiment lasted for 60 days.The results showed that the 96 h LC50 of ammonia nitrogen for juvenile crucians was 289.29 mg/L(95％confidence 264.08～316.90 mg/L),and SC was 28.9 mg/L.The pathological changes of gill tissue were mainly congestion of gill filaments,shortening and curled gill lamella,proliferation of chlorine-secreting cells,and deformation of columnar cells.The degree of ammonia nitrogen damage to gill tissue had dose and time effects.The activity of acid phospha-tase(ACP)in the gill tissue of each ammonia nitrogen group was higher than that of the control group,but there was no significant difference.The activities of alkaline phosphatase(AKP),alanine aminotransferase(ALT),aspartate aminotransferase(AST),catalase(CAT)and superoxide dismutase(SOD)in the ammo-nia nitrogen group were significantly higher than those in the control group.With the extension of exposure time,the enzyme activities of ACP and AKP in the same concentration group showed an increasing trend,while ALT,AST,SOD and CAT increased first and then decreased.In conclusion,ammonia nitrogen stress could inhibit the growth of juvenile crucian carp and damage gill tissues.The degree of damage was positively correlated with stress concentration and time,damaging the antioxidant system and non-specific immune func-tion.
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