Chitosan is a cationic polysaccharide that is primarily derived from chitin, a natural polymer of N‐acetyl glucosamine mainly found in crustacean, insect exoskeletons and fungal cell walls, by exhaustive alkaline deacetylation to varying degrees. Chitosan has been found to have many favourable biological properties including biosafety, biodegradability and biocompatibility. These advantages make it a very promising material for diverse applications. For terrestrial animals, chitosan has been widely used as a feed additive because of its low side effects, enhancing the growth performance, improving immune functions, inhibition intestinal microbial pathogens and lowering cholesterol. Recently, it has been used as a feed additive in fish diets. Moreover, chitosan has gained an attention as an effective agent in aquaculture water treatment. A number of studies have been conducted on the effectiveness of the use of chitosan in aquaculture. Thus, the present review explored the current state of knowledge on the effects of dietary chitosan on farmed aquatic animals including antimicrobial, growth promoting, antioxidant activity and immunostimulation effects, with a particular emphasis on the optimal dose of chitosan. As well as, this review pointed out the possibility of using chitosan in aquaculture water treatment. According to the studies that were discussed in this review, chitosan is considered as a promising material with a massive potential of applications in aquaculture.

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This study investigated the effects of dietary orange peel (OP) on growth performance, feed utilization, antioxidant activity, intestinal microbiota and liver histology of Gilthead sea bream (Sparus aurata) larvae (0.32 ± 0.01 g/fish) (mean ± SD). Fish fed iso‐nitrogenous (480 g/kg protein) and iso‐energetic (23 MJ/kg) diets supplemented with OP at concentrations of 0, 1, 3 or 5 g/kg diet, for 60 days. Growth performance and feed utilization parameters were significantly improved by the elevation of dietary OP level, and the optimum level was 5 g/kg diet. The maximum activity of the total antioxidant capacity, superoxide dismutase, glutathione peroxidase, catalase, alkaline phosphatase enzyme and malondialdehyde in the liver was found at 5.5, 4.6, 3.4, 2.9, 3.7 and 3.8 g OP/kg diet, respectively. All tested bacteria (Staphylococcus spp., Vibrio spp. and Salmonela spp) and total bacterial count decreased significantly in the gut of fish fed high levels of OP (3.0 or 5.0 g/kg). No differences were found in the liver histo‐architecture among treatments after 60 days feeding on OP diets. In summary, dietary OP improved growth rate, antioxidant activity and intestinal microbiota of S. aurata larvae with an optimum range from 2.9 to 5.5 g/kg diet.

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