| In this study, we used the red claw crayfish (Cherax quadricarinatus) as an research object and tried to understand the mechanism of dietary ascorbic acid on Cherax quadricarinatus growth and development based on nutrition, biochemistry, electron microscope and molecular biology methods. The data obtained would provide valuable information to a better understanding on the utilize of ascorbic acid of crustaceans. It would also be helpful to redclaw’s large-scale commercial aquacculture.1. Effect of dietary vitamin C on growth performance and the activity of growth relative enzyme in the redclaw crayfish, Cherax quadricarinatusVitamin C is important in promoting the growth and development of aquatic animals. An 8-week feeding trial was conducted to explore the effect of vitamin C on the growth of the redclaw crayfish, Cherax quadricarinatus. Seven semi-purified practical formulated diets were supplemented with 0,100,400,800,1600,3200 mg kg-1 ascorbic acid.The results showed that different supplements of vitamin C had no significant effect on the suvival and hepatosomatic index of different groups. But vitamin C plays an important role in promoting the growth of the redclaw crayfish, while adding excessive amounts of vitamin C may surely have a growth inhibition affection. The accumulation of vitamin C in the hepatopancreas of the Cherax quadricarinatus increased with the increase of vitamin C in the diets. But when the supplement of vitamin C is more than 400 mg kg-1 diet, the concentration of vitamin C in hepatopancreas tends to saturation. Vitamin C significantly increased the activity of trypsin in the shrimp hepatopancreas, stomach and intestinal of the redclaw crayfish, but had no significant effect on amylase activity.The activity of AKP and ACP can also be increaded by the supplement of vitamin C. Our results suggest that the appropriate supplement of vitamin C has a positive effect on the growth of Cherax quadricarinatus.2. Effects of dietary vitamin C on the tissue ultrastructure of hepatopancreas in Cherax quadricarinatusThe effect of the low concentration, middle concentration, and high concentration of vitamin C on the hepatopancreatic ultrastructure of Cherax quadricarinatus was studied respectively by the method of electron microscope. In the low vitamin C concentration group, the structure of the hepatopancreas had a slight injury, the microvilli were irregularly arranged, parts of them were deciduous and damaged. Nucleus heterochromatinizationand the accumulation of lipid drops decreased.The structure of the hepatopancreas in the middle and the high concentration groups were integrity. But the amount and the quality of the lipid drops in the middle group were better than the high group.The results indicated that the lack of vitamin C have a negetive affect on the structural integrity of the hepatopancreas, thereby affecting the accumulation and metabolism of nutrients in the hepatopancreas. Howere, if the supplement of vitamin C in the diet was too high, it may also inhibit the accumulation of nutrients.3. Molecular cloning, characterization and expression of CatL and the effect of vitamin C on its expression in the red claw crayfish (Cherax quadricarinatus)The CatL cDNA was isolated from the hepatopancreas of Cherax quadricarinatus using RACE-PCR methods, The full-length cDNA of CqCatL obtained from the present study was 1810 bp in length with an open reading frame of 1026 bp, encoding a putative peptide of 341 amino acids. The tissue-specific expression pattern study indicated that the highest expression was observed in hepatopancreas, and the second level of expression was seen in hemocytes, while only very low expressions of CqCatL mRNA were found in intestine and antennal gland. After feeding by seven levels of vitamin C, the mRNA expression of CqCatL was the highest in the 400 mg/kg dietary vitamin C group and significantly higher than the other groups., Our results showed that CqCatL may plays an important roles in the physiological progress of Cherax quadricarinatus, and its gene expression and functions is likely regulated by nutrients, such as vitamin C.4. Molecular cloning, characterization and expression of RXR and EcR and the effect of vitamin C on their expression in the red claw crayfish (Cherax quadricarinatus)The two Molting related genes RXR and EcR were cloned from hepatopancreas of Cherax quadricarinatus, The full-length cDNA of CqRXR obtained from the present study was 1341 bp in length with an open reading frame of 1299 bp, encoding a putative peptide of 432 amino acids. The partial-fragment of the CqEcR gene was 1022bp in length and encoding a putative peptide of 264 amino acids. The tissue-specific expression pattern study indicated that CqRXR and CqEcR mRNA were widely expressed in all tissues, indicating these two genes may play important roles in the growth and development of the Cherax quadricarinatus. And the expression level of these two genes in the groups which contains vitamin C were higher than the group which have no vitamin C. The results indicated that the expression of these two molting related genes had a direct relationship with the addition of vitamin C. The specific regulatory mechanism still needs further experimental verification. |
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