Development of formulated diets for snakehead (Channa striata and Channa micropeltes): Can phytase and taurine supplementation increase use of soybean meal to replace fish meal?

Abstract

Culture of snakehead species is limited in Vietnam and banned in Cambodia because of the reliance of the industry on feeding them “small-size” fish (sometimes called trash fish or low-value fish), many of which are juveniles of commercially important species. In an effort to find substitutes for small-size fish, we conducted a series of experiments to test formulated diets with several levels of soybean meal (SBM) replacement of fish meal. Feeding trials lasted eight weeks, after which survival, growth, food conversion ratio and protein efficiency ratio were compared. In the first two experiments, with Channa striata, we substituted SBM, either with or without supplementation of phytase (20mg/kg) (Experiment 1) or taurine (1g/kg) (Experiment 2), for 0, 20, 30, 40, or 50% of the fish meal. Experiment 1 demonstrated that SBM can replace 30% of the fish meal without, and 40% of the fish meal with, phytase supplementation. Experiment 2 showed again that SBM can replace 30% of the fish meal without, and 40% of the fish meal with, taurine supplementation. The third experiment, with Channa micropeltes, which was done only with phytase supplementation, showed that 40% of fish meal can be replaced by SBM. In all the SBM diets, the essential amino acids (EAA) lysine, methionine and threonine were also added to make their dietary levels equal to those in the fish meal control diet. Use of the SBM replacement diets, in addition to conserving the small-size fish in the wild, would result in economic savings (cost/kg of fish produced) of about 11% compared to diets based on fish meal alone. Statement of relevanceAquaculture is growing rapidly in Vietnam and has the potential to do the same in Cambodia. Production of pangasiid catfish in the Mekong Delta of Vietnam alone exceeded 1 million metric tons in 2008. While some of the food provided to these fish, especially at the larger commercial farms, is formulated feed from commercial feed mills, many small farmers still use “trash fish” from the Mekong in preparing feed by hand at the farm. As aquaculture expands in Vietnam and Cambodia, the fish called snakehead is becoming popular to culture because of its high value in the market. Two species are cultured, the snakehead murrel, C. striata, and the giant snakehead, C. micropeltes. While culture of these is growing in Vietnam, it is prohibited in Cambodia (except for some experimental work) due to its dependence on small fish in the diet. Catfish culture has available commercial pellet diets, so getting farmers to switch from small fish to pellets is a socioeconomic issue, since small-scale catfish farmers often rely on traditional methods and the local availability of small fish. On the other hand, formulated diets do not yet exist for snakehead in Vietnam and Cambodia.