Chitin modulates immunity and resistance of Labeo rohita (Hamilton, 1822) against gill monogeneans

The present study was conducted to delineate the effects of dietary chitin on the immune status and resistance of rohu (Labeo rohita) against gill monogeneans. The study consisted of two experimental trials. In trial-I, chitin (0.5%, 1% and 2%) was incorporated into the control diet (0% chitin) and fed to rohu (15.43 ± 0.79 g) for three weeks. The superoxide anion production, total protein content, myeloperoxidase and alkaline phosphatase activity were measured at weekly intervals. The best stimulatory dose and duration was found to be 1% chitin for 2 weeks based on the observed responses. In trial-II, a new batch of rohu (17.13 ± 1.39 g) were randomly divided into three experimental groups as follows: Negative control ('nc') - fish were fed with the control diet but not exposed to monogeneans; Positive control ('pc') - fish were fed with the control diet and exposed to monogeneans; and fish under chitin supplemented diet ('csd') - fish were fed with 1% chitin and exposed to monogeneans. After two weeks of feeding, infection with gill monogeneans was performed in the 'pc' and 'csd' groups by cohabitation. The experiment was continued for one more month. Various immunological parameters and parasite intensity were measured on 0, 15th and 30th-day post-challenge. The results showed significant enhancement in superoxide anion production, myeloperoxidase and total protein content of fish in the 'csd' group compared to the 'nc' group. However, no significant enhancement was observed in alkaline phosphatase, anti-protease and lysozyme activity. The mean intensity of gill monogeneans was significantly less in the 'csd' compared to the 'pc' group. In conclusion, dietary chitin showed immunostimulatory potential in rohu, predominantly at 1% inclusion level. Further, resistance against gill monogeneans was augmented in rohu following feeding with chitin.