Effect of dietary chitosan on growth performance, haematology, immune response, intestine morphology, intestine microbiota and disease resistance in gibel carp ( C arassius auratus gibelio )

A 75‐day experiment was conducted with juvenile gibel carp ( C arassius auratus gibelio ) (4.80 ± 0.01 g) to evaluate effects of dietary chitosan on fish growth performance, haematology, intestine morphology and immune response. Six isonitrogenous (crude protein: 383 g kg −1 ), isolipid (97.5 g kg −1 ) and isocaloric (gross energy: 16.7 kJ g −1 ) diets were formulated to contain 0, 1800, 4000, 7500, 10 000, 20 000 mg kg −1 chitosan, respectively. The results showed that the growth was depressed when the fish fed with 10 000 mg kg −1 chitosan. Serum cholesterol, triglyceride and low‐density lipoprotein decreased in 10 000 and 20 000 mg kg −1 chitosan. On day 75, blood leucocyte phagocytic activity respiratory burst and alternative pathway of complement haemolytic activity were enhanced in 4000 mg kg −1 chitosan. The number of goblet cell, intraepithelial lymphocyte of mid‐intestine and microvilli height of distal intestine increased at 4000 mg kg −1 dietary chitosan. Dietary chitosan modulated intestine microbiota, depressed pathogen bacteria A eromonas veronii‐ like and improved C ellulomonas hominis ‐like, B acillus oceanisediminis ‐like and two uncultured bacterium‐like species on day 75. Dietary 7500 and 10 000 mg kg −1 chitosan enhanced the protection against A eromonas hydrophila infection. In conclusion, oral administration of dietary 7500 mg kg −1 chitosan for 75 days is recommended for the survival of gibel carp.