Dietary supplementation of chitin and chitosan depresses growth in tilapia, Oreochromis niloticus x O-aureus

The effect of chitin, poly-beta-(1 --> 4)-N-acetyl-glucosamine, and chitosan, a polymer of glucosamine obtained by the deacetylation of chitin, on growth and nutrient digestibility was studied in tilapia, Oreochromis niloticus X O. aureus, fed diets containing fiber at 0, 2, 5 or 10% of a basal diet for 8 weeks. Each diet was fed to triplicate groups of fish with a mean initial body weight of 0.99 +/- 0.01 g. Significantly (P < 0.05) lower body weight gains were observed in fish fed chitin and chitosan containing diets than fish fed the control diet regardless of the supplementation level. The weight gain of fish decreased as dietary chitin and chitosan supplementation level increased (chitin, r = 0.97, P < 0.05; chitosan, r = 0.73, P < 0.05). Higher (P < 0.05) weight gains were observed in fish fed 5 and 10% chitin diets than fish fed the chitosan diets. Feed conversion ratio (FCR) followed the same pattern of the weight gain. Lipid and dry matter digestibilities were lower in fish fed the 10% chitin diet than in fish fed the control diet. Lower lipid and dry matter digestibilities and lower body lipid content were observed in fish fed chitosan containing diets irrespective of supplementation level. Fish fed 2 and 5% chitin diet had higher lipid digestibility than fish fed chitosan diet. Body lipid content of the fish reflect the general pattern of the lipid digestibility. These data suggest that both chitin and chitosan supplementation depresses tilapia growth regardless of the supplementation level. (C) 1999 Elsevier Science B.V. All rights reserved.