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

A 75-day experiment was conducted with juvenile gibel carp (Carassius 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 a 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 ka(-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, intra-epithelial 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 Aeromonas veronii-like and improved Cellulomonas hominis-like, Bacillus oceanisediminis-like and two uncultured bacterium-like species on day 75. Dietary 7500 and 10 000 mg kg(-1) chitosan enhanced the protection against Aeromonas hydrophila infection. In conclusion, oral administration of dietary 7500 mg kg(-1) chitosan for 75 days is recommended for the survival of gibel carp.