| This paper consists of two tolerance studies related to feed additives in fish. One was conducted to evaluate the upper inclusion level of daidzein, one of the main isoflavones found in soybean, in the diet of freshwater fish using gibel carp as target animal; The other one focused on the upper inclusion level of cobalt dichloride in the diet of marine fish using turbot as target animal. The results and conclusions are summarized as follows:1. A tolerance and safety assessment of daidzein in gibel carp (Carassais auratus gibebio)Effects of daidzein inclusion in the diet of gibel carp was assessed in terms of growth performance, immune response, disease resistance, antioxidant activity, hormone levels, daidzein tissue residue, as well as intestinal and liver morphology. The dietary daidzein inclusion levels were 0.40,200, and 400 mg/kg and six replicates of 30 fish were used for each group. No mortality was observed during the 10-week feeding trial. The growth performance of experimental fish was not significantly affected by dietary daidzein supplementation (P>0.05). However, the non-specific immune response, resistance to Aeromonas hydrophila, antioxidant activities.17P-estradiol level, vitellogenin concentration, gonadosomatic index (GSI). and intestinal morphology were significantly affected by dietary daidzein (P<0.05). A dietary dose of 400 mg/kg daidzein significantly decreased the GSI, increased 17β-estradiol and vitellogenin concentrations (P<0.05), and impaired the intestinal structure. The daidzein residue in muscle of gibel carp was significantly increased by the high level (400 mg/kg) of dietary daidzein (P<0.05). Equol, a metabolite of daidzein produced by the gut microflora during the process of digestion, however, was not detected in fish muscle among all the treatments. The present study demonstrated that 40 mg/kg daidzein was safe to be included in the diet of gibel carp, and a safety margin of 5 folds of the use-level (40 mg/kg) was determined.2. A tolerance and safety assessment of cobalt dichloride in turbot (Scophthalmus maximus L.)Effects of dietary cobalt on survival, growth performance, haematological parameters, antioxidases activities, digestive enzymes activities, VB12 contents in serum and liver, tissue cobalt residue, and intestinal and liver morphology of turbot were assessed to determine the upper inclusion level of cobalt in the turbot diet. Graded levels of cobalt (0,3.6,18 and 36 mg/kg. respectively) (supplemented in the form of cobalt dichloride) were included into the basal diet to formulate four isonitrogenic and isocaloric experimental diets. Six replicates of 30 fish were used for each treatment group. No significant difference in the mortality was observed among all the experimental groups (P>0.05). Compared with the control group, the growth performance of fish was not affected by dietary cobalt supplementation of 3.6 or 18 mg/kg (P>0.05), however,36 mg/kg dietary cobalt significantly decreased the feed intake, specific growth rate, hepatosomatic index and viscerosomatic index of fish (P<0.05). Supplementation of 18 and 36 mg/kg cobalt in the diet significantly decreased the activities of serum catalase, aspartate transferase and alkaline phosphatase in fish (P<0.05). The activity of stomach amylase was significantly decreased by dietary supplementation of 18 and 36 mg/kg cobalt (P<0.05), while dietary supplementation of 18 mg/kg cobalt significantly decreased the activity of trypsin (P<0.05). With increasing inclusion level of dietary cobalt, the glucose and VB12 content in serum and liver and the cobalt residue in liver and muscle increased significantly (P<0.05). Histological studies showed no lesions in the intestine of fish from all treatment groups. However,18 and 36 mg/kg dietary cobalt showed some damage to the liver tissue as widened hepatic sinusoidals were observed. The present study showed that 3.6 mg/kg cobalt was safe to be included in the diet of turbot. |
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