A sixty-day feeding trial was conducted to determine the ascorbic acid (AA) requirement for growth of striped catfish, Pangasianodon hypophthalmus juveniles. Seven isonitrogenous and iso-energetic (370 g protein per kg and 19.6 MJ/kg) purified diets were prepared with different levels of ascorbic acid such as control (0), T 1 (17.5), T 2 (35), T 3 (70), T 4 (175), T 5 (350) and T 6 (700) mg ascorbic acid (L-ascorbyl-2-polyphosphate) equivalent per kg diet. Fish with a mean body weight of 3.2-3.4 g were stocked (fifteen fish per tank) in triplicates following a completely randomized design. Each group was fed to satiation twice a day for 60 days. Significant differences were observed in growth, survival, body composition and metabolic enzymes activities with different dietary ascorbic acid levels. Maximum weight gain, specific growth rate (SGR) and protein efficiency ratio (PER) were found in fishes fed with 35 mg AA per kg diet, supported by best feed conversion. Fish fed a diet containing vitamin C had the highest activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) compared to those fed with vitamin C-depleted diets.In this study, based on using broken-line regression analysis, the dietary vitamin C requirement for growth of P. hypophthalmus juveniles was estimated to be in the range of 46-76 mg AA per kg, depending on the criterion used, growth and liver storage.Our results will be helpful for the formulation of cost-effective ascorbic acid incorporated diets for striped catfish, P. hypophthalmus.
K E Y W O R D Sascorbic acid, growth, L-ascorbyl-2-polyphosphate, Pangasianodon hypophthalmus, vitamin C requirement
| INTRODUCTIONVitamin C (ascorbic acid) is considered as one of the essential nutrients required for growth and immunity in fish (Asaikkutti, Bhavan, Vimala, Karthik, & Cheruparambath, 2016;Dabrowski, 2000;Khan, Zuberi, & Ullah, 2015;Lim & Lovell, 1978; NRC, 2011;Pimpimol, Phoonsamran, & Chitmanat, 2012;Xu et al., 2016). Ascorbic acid (AA) has an extensive role in the enhancement of growth, collagen synthesis, iron metabolism, haematology, reproduction, stress physiology, wound healing and immune response in fish (Albrektsen, Lie, & Sandnes, 1988;Anbarasu & Chandran, 2001;Halver, Smith, Tolbert, & Baker, 1975;Roberts, Davies, & Pulsford, 1995). Many of the farmed fishes, such as ictalurids, cichlids and cyprinids, cannot synthesize vitamin C de novo because they do not contain the enzyme, L-gulono-1,4-lactone oxidase (Chatterjee, 1973;Dabrowski, 1994;Moreau, Dabrowski, & Sato, 1999;Xie, Niu, Zhang, & Bao, 2006;Yamamoto, Sato, & Ikeda, 1978). Ascorbic acid is soluble in water, and thus, leaching of this vitamin from feeds can be a serious issue (Abdelghany, 1996; Hilton, Cho, Brown, & Slinger, 1979; Hilton, & Slinger, 1977;Soliman, Jauncey, & Roberts, 1986). Wilson and Moreau (1996) reported that AA is not stable in the native form as 50 mg/kg of the supplemental AA will be destroyed during the feed manufacturing process. Therefore, accur...