Chitosan and iron as feed additive: effects on growth and feed intake in rainbow trout (Oncorhynchus mykiss)

A feeding trial was conducted in rainbow trout juveniles to investigate the growth performance, feed utilization, and digestibility after the inclusion of feed additives iron (II) sulphate and chitosan in the diets. Four experimental diets were formulated with a combination of different iron (II) sulphate heptahydrate (FeSO4) levels of 150 and 300 mg kg-1, respectively, with or without 2.5 g kg-1 chitosan supplementation. Triplicate groups of fish (10.7 ± 0.05 g) were randomly distributed in tanks with a re-circulating aquaculture system at a stocking density of 35 fish per tank. The fish were fed each experimental diet twice daily until apparent satiation for 60 days. As a result, the fish fed a dietary treatment G3 with 150 mg kg-1 FeSO4 and 2.5 g kg-1 chitosan achieved significantly higher growth, body weight gain (BWG) and specific growth rate (SGR) compared to other dietary treatments. The growth, BWG and SGR in fish fed 300 mg kg-1 FeSO4 and 2.5 g kg-1 (G4) was almost similar to the dietary treatment with feed additive of FeSO4 without chitosan inclusion (G1 and G2) without significant difference (P>0.05). Similarly in feed utilization, fish fed diet group G4 of 300 mg kg-1 FeSO4 with 2.5 g kg-1chitosan had a better daily feed intake, feed conversion ratio and feed efficiency without significant differences (P>0.05). The apparent digestibility coefficient for crude protein and crude lipid of the diet with chitosan supplementation were comparable to diet treatment G1 with significant differences (P<0.05). Survival was not affected by the experimental diets. This study showed that rainbow trout can utilize a diet supplemented of FeSO4 and better performance was observed with the inclusion of 2.5 g kg-1chitosan.