| The study was conducted to GIFT tilapia (Oreochromis niloticus), the effects of dietary rapeseed meal levels on growth performance, body composition, liver tissue structure and blood biochemical indices, and the effects of different levels of rapeseed meal supplemented with calcium iodate on growth performance, body composition, liver tissue structure and blood biochemical indices, The contents and results are as follows:1. A 10-week feeding experiment was conducted to evaluate the effects of dietary rapeseed meal levels on growth, liver tissue structure and blood biochemical indices indices of juvenile GIFT tilapia(Oreochromis niloticus) (initial body weight 4.82±0.46g). Five isonitrogenous (crude protein 34%) and isoenergetic (total energy 19.2 kJ/g) diets were formulated to contain rapeseed meal 15.0%(control group),30.0%,45.0%,60.0%, 75.0% respectively. The results showed that weight gain rate (WGR), specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) of GIFT tilapia decreased with increasing the level of rapeseed meal,60.0% and 75.0% groups were significantly lower than those in the control group (P< 0.05),30.0% and 45.0% groups had no significant differences with the control (P>0.05). No significant differences in hepatosomatic index (HSI), viscerosomatic index (VSI) and survival rate (SR) were observed among treaments. Proximate composition in whole body of GIFT tilapia, crude protein content of 60.0% group was significantly higher than that in the control group (P <0.05), crude fat content of 60.0% group was significantly lower than that in 30.0% group, no significant differences in moisture and ash were observed among treaments (P >0.05). Proximate composition in muscle of GIFT tilapia, crude protein content of 45.0% group was significantly higher than that in the control group (P<0.05), crude fat content decreased with increasing the level of rapeseed meal, crude fat content of 75.0% group was significantly lower than that in control group, no significant differences in moisture and ash were observed among treaments (P>0.05). The number of hepatocytes with empty vacuoles degeneration and nuclear migration increased progressively with increasing the level of rapeseed meal, liver tissue structure damaged increasingly. No significant effects of dietary rapeseed meal levels on the content of the serum albumin (ALB), total protein (TP), total cholesterol (T-CHO), triglycercide (TG), triiodo-thyronine(T3), thyroxine(T4), T3+T4, T3/T4 and lysozyme (LZ). Alkaline phosphatase (ALP) activity increased with increasing the level of rapeseed meal,75.0% group was significantly higher than the control (P< 0.05), while superoxide dismutase (SOD) activity declined with increasing the level of rapeseed meal,60.0% group was lowest, and significant difference with the control (P< 0.05). In this condition, a percentage of no more than 45.0% of dietary rapeseed meal in juvenile GIFT tilapia was advisable.2. In a completely randomized design with 2*3 factorial arrangements and 3 replicates, juvenile GIFT tilapia (Oreochromis niloticus) at an initial body weight of 4.37±0.44 g were ued to evaluate the effect of different levels of rapeseed meal (RSM) supplemented with calcium iodate on growth, body composition, liver tissue structure and blood biochemical indices of GIFT tilapia. The RSM was ued at the levels of 30 (control) and 60 percent for 10 weeks. The iodine levels added into the diets were 3 mg/kg (control),6 mg/kg and 12 mg/kg. Six isonitrogenous (crude protein 34%) and isoenergetic (total energy 19.2 kJ/g) diets were formulated. I1 (RSM 30%, iodine 3 mg/kg),12 (RSM 30%, iodine 6 mg/kg),13 (RSM 30%, iodine 12 mg/kg),14 (RSM 60%, iodine 3mg/kg),15 (RSM 60%, iodine 6 mg/kg),16 (RSM 60%, iodine 12mg/kg) respectively. The results showed that, weight gain rate (WGR), specific growth rate (SGR) of 14 group were significantly lower than those of other groups (P<0.05), no other significant differences between groups (P> 0.05). weight gain rate and specific growth rate increased progressively with increasing the level of iodine, weight gain of 12 mg/kg iodine level was significantly higher than that of 3mg/kg iodine level (P<0.05), specific growth rates of 6 mg/kg and 12 mg/kg iodine level were significantly higher than that of 3 mg/kg iodine level(P<0.05). feed efficiency ratio (FER) and protein efficiency ratio (PER) of 14 group were significantly lower than those of I1,12 and 13 groups (P<0.05), and no significant difference with 15 and 16 group (P> 0.05), feed efficiency ratio (FER) and protein efficiency ratio (PER) of 30% RSM level were significantly higher than the level of 60% RSM level. Hepatosomatic index (HSI) of 30% RSM level decreased with increasing the level of iodine, Hepatosomatic index of 13 group was significantly lower than that of I1 group (P<0.05). No significant differences in viscerosomatic index (VSI) and survival rate (SR) were observed among groups Proximate composition in whole body of GIFT tilapia, crude protein content and moisture content of 30% RSM level were significantly lower than that of 60% RSM level (P<0.05), crude fat content of 30% RSM level was significantly higher than that of 60% RSM level (P<0.05). Crude fat content of 3 mg/kg iodine level was significantly higher than 6 mg/kg and 12 mg/kg iodine level (P<0.05), while ash content was significantly lower than that of 6 mg/kg and 12 mg/kg iodine level (P<0.05). Proximate composition in muscle of GIFT tilapia, crude protein content of 13 group was significantly higher than that of 12 group (P<0.05), no other significant differences between groups (P>0.05), no significant differences in moisture, ash and crude fat content were observed among treaments (P>0.05); In iodine levels, crude protein content of 6 mg/kg iodine level were significantly lower than that of 3 mg/kg iodine level (P<0.05). No significant effects of different levels of rapeseed meal supplemented with calcium iodate on the content of the serum albumin (ALB), total protein (TP), total cholesterol (T-CHO),triglycercide (TG), triiodo-thyronine(T3), thyroxine(T4), and the activity of lysozyme (LZ), alkaline phosphatase (ALP), superoxide dismutase (SOD). Observed by the liver slices, vel of 30% rapeseed meal normal liver cells, Only individual hepatocytes showing nuclear migration(NM). With increasing the level of iodine, of 60% rapeseed meal level, the situation of liver damage constantly improved. By a massive of hepatocytes of 14 group showing nuclear migration and vacuolar degeneration (V), to the reduction of nuclear migration and vacuolar degeneration of hepatocytes in 15 group, hepatocytes of 16 group close to normal, this is the best proof. In this experiment, high dietary levels of rapeseed meals (60%) supplemented with iodine could alleviate or eliminate the adverse effects of toxins in diets on growth and liver tissue structure of juvenile GIFT tilapia. |
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