Effect of chitosan diet on intestinal histology, body composition and salinity and thermal stresses resistance in Caspian kutum (Rutilus frisii kutum, Kamenskii 1901) fingerlings

This study was conducted to evaluate the effect of the chitosan diet on the intestinal histology, body composition and resistance towards salinity and thermal stresses in Caspian kutum (Rutilus frisii kutum) fingerlings. This research, using a completely random design, consisted of 0.25, 0.5, 1, and 2 g levels of chitosan per kg for each commercial diet of the Caspian kutum in three repetitions. The Kutum fingerlings, with an average weight of 1.76 ± 0.15 g, were fed with the experimental diets for 8 weeks. At the end of the experiment, tissue sections were prepared by cutting 5mm-thick samples from the intestines of the fish. To evaluate the resistance to salinity and thermal stresses, the fingerlings were exposed to a salinity stress of 11 ppt and 13 ppt and temperatures of 30 °C and 34 °C, after which the survival rate was calculated. Microscopic observations showed that the intestinal villi height in the fish fed with the diet containing 1 g kg-1 of chitosan significantly increased to 319.93 µm compared to the control group (P0.05). Fish survival rate after 11 ppt and 13 ppt salinity stress showed no statistically significant difference (P>0.05), but the survival rate of the fish fed with the diet containing 1g kg1 of chitosan after experiencing the 34 °C thermal stress significantly increased to 70% (P<0.05). The results suggest that a chitosan level of 1g kg-1 in the diet can not only affect the survival rate and resistance of kutum fingerlings against thermal stress, but can also affect the height of the intestinal villi