50 JUNE 2018 • WORLD AQUACULTURE • WWW.WAS.ORG striata can be weaned beginning at 17 days after hatch (DAH) and can fully accept pelleted diets 10 days later. However, the giant snakehead Channa micropeltes must begin weaning later at 40 DAH and the weaning period to full acceptance of pellet diets requires 30 days. Successful completion of this step allowed for the testing of pellet diets using standard fish nutrition experimental techniques. Development of Pelleted Diets for Snakehead in Vietnam Based on previous work at the University of Rhode Island (URI) on replacement of fishmeal in diets for summer flounder (Enterria et al. 2011, Lightbourne 2011), experiments were designed and conducted at CTU to determine the maximum levels of fishmeal that could be replaced by plant proteins with and without the addition of supplemental amino acids, taurine and phytase (Hien et al. 2015b) in diets for C. striata. These experiments showed that 40 percent of fishmeal could be replaced by soybean meal, provided certain amino acids and phytase were added. Based on these laboratory experiments, pond trials were then conducted at CTU to compare the new pelleted diet against the traditional diet of chopped small fish in terms of fish survival and growth, and product quality determined in a sensory evaluation. Further pond trials were conducted on commercial farms to evaluate the commercial feasibility of using pelleted diets. All findings were extremely positive (Hien et al. 2016a). There were no significant differences between fish raised using pelleted diets versus those fed chopped small fish in the CTU pond trials. Furthermore, economic analysis indicated that profits were greater using pelleted diets on the commercial farms tested. The CTU diet formulation was shared with feed mills in the Mekong Delta by CTU researchers, along with further outreach and demonstration projects for farmers in An Giang and Dong Thap provinces. This led to widespread adoption of pelleted diets by snakehead farmers in Vietnam (Fig. 2). In recent years, special efforts have been made to educate women to become snakehead farmers (Fig. 3). Economic Analysis of Alternative Snakehead Feed Replacing small-sized fish for snakehead aquaculture with pelleted feed would reduce the pressure on stocks of small fish. Grimm-Greenblatt et al. (2015) studied the economics of this replacement strategy for snakehead culture in Vietnam. Economic engineering methods were used to assess the effects of pelleted feed for low-, medium- and high-productivity scenarios. The study compared net present values (NPV), internal rates of return (IRR) and differences in NPV between farms using pelleted feed and those using small fish. It also included sensitivity analyses that related NPV and IRR to increased snakehead prices. Results demonstrated strong economic incentives for farms to use pelleted feed. Over time, pelleted feed became less expensive and more cost effective for medium- and lowproductivity farms. NPVs were more sensitive to reduction in the cost of pelleted feed than to increased cost of small fish or the cost of capital. Investigation of Soy Protein Concentrate and Immunostimulants Again based on previous work with summer flounder at URI (Ward 2014, Ward et al. 2016), we investigated whether soy protein concentrate (SPC) might be a better component than soybean meal in pelleted diets for snakehead. SPC has a higher protein level than soybean meal and few to none of the anti-nutritional compounds found in soybean meal. Flounder work at URI had indicated that certain oligosaccharide compounds (stachyose and raffinose) in soybean meal, but missing from SPC, serve an immunostimulatory function. Experiments at CTU indicated that SPC could not be added to snakehead diets at levels greater than 40 percent, i.e., similar to soybean meal (Hien et al. 2016b). In addition, SPC is considerably FIGURE 2. A Vietnamese farmer feeding snakehead with the newly developed pellet diet. FIGURE 3. Training for women on seed production, grow-out and disease prevention and treatment of snakehead in the provinces of An Giang, Dong Thap and Tra Vinh, Vietnam in April, 2017. Replacing small-sized fish for snakehead aquaculture with pelleted feed would reduce the pressure on stocks of small fish. There are strong economic incentives for farms to use pelleted feed. Over time, pelleted feed became less expensive and more cost effective for medium- and low-productivity farms. NPVs were more sensitive to reduction in the cost of pelleted feed than to increased cost of small fish or the cost of capital.
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