Interaction of low-level dietary supplementation of Chlorella vulgaris Beijerinck, 1890, and feeding duration on growth hormone, growth performance and serum biochemistry of red hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus).

Chlorella is one of the most widely accepted Chlorophyta used by many as livestock and aquaculture feed. Nonetheless, different studies on the overall performances of fish reported the unfavourable effect of high-level supplementations of Chlorella vulgaris. The current study determined the impact of low-level dietary supplementation of C. vulgaris alongside the different feeding durations and their interactions on the growth hormone (GH), growth performances, serum-biochemical indices, hepatic function and some immunological parameters of red hybrid tilapia. The fingerlings (mean weight: 14.25 ± 0.01 g, length: 13.5 ± 0.49 cm) were fed diets containing 0, 0.99%, 2.91% and 4.76% of C. vulgaris powder per kilogram dry diet for 90 days. GH, growth performance, serum-biochemical indices (total serum protein, albumin, globulin, glucose, aspartate aminotransferase and alanine aminotransferase) and some immunological (respiratory burst and lysozyme activities) parameters of the fish were examined after 30, 60 and 90 days of feeding. The results demonstrated that tilapia fed C. vulgaris-supplemented diets showed increased levels of respiratory burst, lysozyme, albumin and total protein, GH and growth performances (P < 0.05), and the effects were duration dependent. After the 90 days of feeding, there was no adverse effect on the hepatic function of the fish. Besides, low survivability was observed in the control group than in the group fed the experimental diets. The group fed the diet supplemented with 4.76% C. vulgaris had significantly higher (P < 0.05) lysozyme activity throughout the duration of the feeding experiment. These results indicate that C. vulgaris enhanced growth performances, GH concentration, serum-biochemistry and some immunological parameters of red hybrid tilapia.

Dietary astaxanthin augments disease resistance of Asian seabass, Lates calcarifer (Bloch, 1790), against Vibrio alginolyticus infection.

This investigation describes the impacts of dietary provisioning with astaxanthin on hemato-biochemistry, non-specific immunity, and disease resistance of the Asian seabass, Lates calcarifer, against the virulent Vibrio alginolyticus; with specific reference to dose-response associations and variations over different post-infection periods (0-, 7-, and 14-day). Triplicate groups of fish weighing 28 g, on average, were fed various diets (C, the control or astaxanthin-free; AXT50, 50 mg astaxanthin kg-1 diet; AXT100, 100 mg astaxanthin kg-1 diet; and AXT150, 150 mg astaxanthin kg-1 diet) for 90 days and subsequently challenged with V. alginolyticus at the end of the feeding period. Experimental infection unveiled that supplemented fish demonstrated significant improvements (P < 0.05) of hematological parameters (white blood cell [WBC] and red blood cell [RBC] counts, and hemoglobin and hematocrit levels) when fed diets with elevating supplemental doses of astaxanthin through distinct post-infection periods (0-, 7-, and 14-day). Furthermore, the administration of dietary astaxanthin at escalating levels markedly enhanced (P < 0.05) the serum biochemical profile (aspartate aminotransferase [AST], alanine aminotransferase [ALT], glucose, cortisol, cholesterol, and triglyceride contents) of challenged fish, resulting in better welfare. Significantly higher (P < 0.05) contents of serum total protein were observed in supplemented fish, as opposed to the control. Additionally, immunological defense mechanisms (lysozyme activity, phagocytic activity, respiratory burst activity, and total serum immunoglobulin) of challenged fish were pronouncedly elicited (P < 0.05) following the ingestion of astaxanthin. Besides, the supplementation with dietary astaxanthin significantly augmented (P < 0.05) the post-challenge survival rate of fish. Collectively, the results manifest that supplementary feeding of astaxanthin is effective in reinforcing fish immunocompetence and disease resistance against V. alginolyticus infection.