Effect of dietary chitosan on challenged Dicentrarchus labrax post larvae with Aeromonas hydrophila

Effect of different dietary squilla chitosan (Csq) concentrations: 0 (control), 0.5, 1 and 2 g 100 g^–1 diets were studied for weaned sea bass (Dicentrarchus labrax) post larvae. Post larvae were challenged with Aeromonas hydrophila after 5 feeding days, in order to monitor the prophylactic effect on the Csq fed larvae. The experiment started with an average initial weight of 50 ± 2 mg and total length of 12 ± 2 mm for post larval stage (40 days post hatch; dph), then continued feeding diets for a period of 20 days. Larvae survival percentage (%), mean total length (TL), width (W), total weight (TW), total weight gain (TWG), average daily weight (ADW) and specific growth rate (SGR) were recorded as morphometric measurements representing growth compared to the control groups. The results revealed that 1g Csq 100 g^–1 diet at P < 0.05 was the most effective concentration that achieved higher survival percentages; 94.5 ± 0.5 and 74 ± 2.0%, increasing the specific growth rate by 7.22% and 5.77% for non challenged and challenged weaned larval groups, respectively. Otherwise, the control challenged group displayed the lowest performance in all assayed parameters with the coincidental decrease in the survival % and specific growth rates. Similarly, lower growth performance was also observed at 2 g 100 g^–1 diet. Thus, the incorporation of chitosan at a level of 1g in fish diet enhanced the performance and reduced the fish mortality under stress conditions.