| In this study, toxic effects of dietary cadmium(Cd) on tilapia were investigate, and the effects of Chitosan(CS) on alleviating toxicity of dietary Cd to tilapia were evaluated. The main results were showed as follows: 1. Study of the acute toxicity of dietary Cd on tilapiaOne hundred and eighty fish were randomly divided into six treatment groups with three replicates in each group, and each replicate 10 fish. Fish were exposed to dietary Cd at concentrations of 0%, 0.10%, 0.25%, 0.50%, 1.00% and 2.00%, respectively. The 96 h LD50 and the safe dose of Cd in tilapia feed were calculated. The results showed that the 96 h LD50 of dietary Cd in tilapia was 49.67±6.11mg/kg·BW, and the safety limit of Cd in tilapia diet was 0.47mg/kg. The Cd in tilapia diet was a rank toxic substance. 2. Study of the subchronic toxicity of dietary Cd on tilapiaThree hundred fish were randomly divided into five treatment groups with four replicates in each group and 15 fish in each replicate. The dietary Cd level of the five treatment groups were 0(control group), 50, 100, 200 and 400 mg/kg, respectively. Compared with the control group, WGR and SGR in 200 mg/kg dietary Cd group were decreased significantly(P<0.05), and the DFI in 50 mg/kg dietary Cd group was decreased significantly(P<0.05). There was no significant difference in the FR, FCR and SR between the control group and dietary Cd groups(P>0.05). The activities of amylase and protease in intestine of 50 mg/kg dietary Cd group were decreased significantly(P<0.05). The ALB level of 50 mg/kg dietary Cd group was decreased significantly and the GPT level of 50 mg/kg dietary Cd group was increased significantly(P<0.05). The levels of BUN and GOT of 50 mg/kg dietary Cd group were increased significantly(P<0.05). The contents of MDA were increased with the level of dietary Cd. The levels of T-AOC were decreased with the dietary Cd levels. The activities of CAT and SOD were highest in 50 and 200 mg/kg Cd groups compared with other groups, respectively. It indicated that toxic effect could be induced to tilapia by 50 mg/kg dietary Cd. 3. Effects of CS on the acute toxicity of dietary Cd to tilapiaThree hundred and sixty fish were divided into two treatment groups(the control group and the experimental group). The fish were exposed to dietary Cd at concentrations of 0%, 0.1%, 0.25%, 0.5%, 1.0% and 2.0% in the control group. The dietary Cd level of the experimental group with 10 percent of chitosan was the same as the control group. 96 h LD50 of two treatment groups were calculated. The results showed that 96 h LD50 of the experimental group was very significantly higher than the control group(P<0.01). It suggested that the toxicity of dietary Cd to tilapia had been to some extent alleviated by supplementation of CS in the diet. 4. Effects of CS on subchronic toxicity of dietary Cd to tilapiaTwo hundred and fourty fish were randomly divided into four treatment groups with four replicates in each group and 15 fish in each replicate. Dietary Cd level were 50 mg/kg in all groups. The four treatment groups were Cd group, Cd+0.5%CS group, Cd+1.0%CS group and Cd+1.5%CS group, respectively. The trial period was 7 weeks. In order to investigate the Cd levels in intestine, muscle, feces and farming water, hydrostatic test was carried out meanwhile the normal group was supplemented after the feeding experiment. Compared with Cd group, WGR, SGR and DFI of Cd+0.5%CS group were significantly increased(P<0.05), the protease activities in tilapia intestine of Cd+0.5%CS group were significantly increased(P<0.05), the lipase activities in tilapia intestine of Cd+1.0%CS group were significantly increased(P<0.05), the amylase activities in tilapia intestine of Cd+1.5%CS group were significantly increased(P<0.05), the levels of BUN and GPT of Cd+0.5%CS group were significantly decreased(P<0.05), the levels of T-AOC and the activities of SOD of CS supplemention groups were significantly increased, and the activities of CAT of CS supplemention groups were significantly decreased(P<0.05). Compared with the normal group, Cd levels in intestine, muscle, feces and farming water of Cd group were significantly increased(P<0.05). Compared with Cd group, Cd levels in intestine, muscle and farming water of CS supplemention groups were significantly decreased(P<0.05), Cd levels in feces of CS groups were significantly increased(P<0.05). The results suggested that the toxicity of dietary Cd on tilapia might be alleviated by supplementation with CS in diet. The adsorption by CS in fish intestinal tract might play an important role on alleviating the toxicity of dietary Cd.In conclusion, strong toxicity could be induced by 50 mg/kg dietary Cd to tilapia, and the toxicity of dietary Cd on tilapia could be alleviated by supplemention with proper level of CS in diet. |
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