PELLET FEED IMPROVEMENTS THROUGH VITAMIN C SUPPLEMENTATION FOR SNAKEHEAD FISH Channa striata CULTURE IN VIETNAM

In Vietnam, snakehead fish is considered as one of the most valuable cultured fish. However, enhancement of fish health is an important issue for snakehead culture, because bacterial disease is a serious problem and vertebral anomalies have also been observed. Our objective was to determine optimal vitamin C levels in feed for snakehead fish culture. Several benefits have been attributed to ascorbic acid (AA) supplementation in fish such as growth, survival, reduction of skeletal deformities, disease resistance and stress response.

Laboratory feeding trial: The study was conducted to find out the optimal dietary vitamin C levels in terms of the growth performance of snakehead fish and economic aspects. The 8-week growth trial included six treatments with five replications each: 0, 125, 250, 500, 1000 and 2000 mg vitamin C (L-ascorbate-2-monophosphate) equivalent kg^-1 diet. The diet, based primarily on soybean meal (SBM) and fish meal, contained 45% protein, 9% lipid and 4.2 Kcal.g¹. Eighty snakehead fingerlings (6.24±0.17 g.fish¹) were assigned randomly in 0.5 m³composite tanks with continuous aeration. Fish were fed twice daily. Growth rates and protein efficiency ratio were significantly greater in treatments with vitamin C supplementation compared with control treatment and optimal growth was obtained at 500 mg.kg^-1. Red blood cell counts and lysozyme in treatments with vitamin C supplementation tended to rise significantly proportional to the concentration of vitamin C. White blood cell counts in treatments with vitamin C supplementation were 2.1-3.6 times higher than those in the treatment without vitamin C supplementation. A bacterial challenge following the feeding trial showed best survival for fish fed AA levels of 250 mg.kg^-1 or more.

On-farm pond trial: Based on our laboratory results, effects of AA on snakehead in ponds to simulate farm conditions was tested using the following treatments: (i) commercial feed; (ii) commercial feed plus hand mixed AA at 500 mg.kg^-1; (iii) commercial feed plus hand mixed AA at 750 mg AA.kg^-1; (iv) commercial feed plus hand mixed AA at 1000 mg AA.kg^-1; (v) SBM diet without AA; (vi) SBM diet plus 500 mg AA.kg^-1; (vii) SBM diet plus 750 mg AA.kg^-1; (viii) SBM diet plus 1000 mg AA.kg^-1.The experiment was conducted in two experimental ponds (only SBM diet without AA placed in one pond and the rest in the other pond) with three replicate hapas each. Stocking density was 150 fish.m² and culture period was 5 months until market size was attained. Growth rates and protein efficiency ratio were greater in treatments with vitamin C supplementation compared with control treatment. Production cost was lowest for fish fed AA levels of 500 mg.kg^-1

Acknowledgment

This research was funded by the AquaFish Innovation Lab under USAID CA/LWA No. EPP-A-00-06-00012-00 and by US and Host Country partners. The opinions expressed herein are those of the author(s) and do not necessarily reflect the views of the AquaFish CRSP or the US Agency for International Development