WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2015 43 The production of tilapia, like other fed species, has been constrained by the cost of feeds, which can account for about 70 percent of the production costs of tilapia in several countries and regions (Bolivar et al. 2006, Elnady et al. 2010). There have been many attempts to replace expensive animal protein in tilapia feeds with plant protein sources, such as soybean meal, groundnut seed cake and others. Although animal protein replacement in tilapia feeds has been successful, feed continues to represent a major cost item in tilapia production. Rural pond aquaculture is typically practiced as small-scale fish polyculture systems, where natural productivity is enhanced with fertilizers and fish or shrimp are provided with supplemental feeds. The major constraints for small-scale, resource-poor farmers are fish feeds and chemical fertilizers, which are expensive and not readily available. Reducing feed costs in aquaculture is, therefore, important for long-term sustainability of rural aquaculture, where profit margins often tend to be rather small. There is potential to reduce feed costs in aquaculture by using less expensive feed and through adoption of prudent feed management strategies. Field trials in Nepal, Thailand, Vietnam, Kenya and China has demonstrated that several best practices in pond culture of tilapia species can reduce feed costs by half (Diana et al. 1994, Yi et al. 2001). These practices include adequate fertilization using organic manures, fertilization and supplementary feeding, feeding on alternate days or reducing the daily feed ration to half the satiation level with adequate fertilization. These trials have demonstrated reasonably good growth and better performance of tilapia at relatively lower feeding costs. These approaches rely on the dynamics of pond productivity in response to different fertilizer and feed treatments. The overall purpose of the research trials was to develop a low-cost pond culture system that could lead to increased Low-Cost Tilapia Production With Fertilization and Supplementary Feeding Julius O. Manyala, Robert S. Pomeroy, Phanna Nen, Kevin Fitzsimmons, Madhav K. Shrestha and James S. Diana profits, improve the supply of high quality fish protein to communities with limited food resources, and contribute to the overall growth of national aquaculture sectors. This article highlights the effects of combinations of fertilizers and feed on tilapia productivity in small earthen ponds. Experiments were conducted in Nepal, Cambodia and Kenya using a similar experimental design, stocking density and feeding regime. Experimental Design Experiments were carried out in Kenya (University of Eldoret), Nepal (Institute of Agriculture and Animal Science) and Cambodia (Freshwater Aquaculture Research and Development Center). Earthen ponds were 100 m2 in Kenya, 150 m2 in Nepal and 300 m2 in Cambodia (Fig. 1). Pond depth ranged from 70 to 100 cm. Twelve ponds were used in each location, four per treatment. The three treatments used in the experiment at each location were 1) fertilization only, 2) feed only, with a feeding rate of 3 percent of body weight daily, and 3) fertilization and feeding at 1.5 percent body weight daily. Fertilized ponds received weekly applications of diammonium phosphate and organic manure or urea at 4 kg/ha N and 1 kg/ha P. Tilapia in feed treatments were offered 25-30 percent crude protein diets twice daily in midmorning and late afternoon. Ponds were stocked with sex-reversed male Nile tilapia Oreochromis niloticus in Kenya and Nepal and mixed-sex Nile tilapia in Cambodia. The initial weight of fingerlings used to stock ponds was 5 g in Kenya, 6 g in Nepal and 2.5 g in Cambodia. Fish were stocked at 2/m2 in Kenya and Cambodia and 1/m2 in Nepal. Standard methods were used to characterize pond water quality (Boyd 1979, Egna et al. 1987, APHA 2012). Fish were grown for 120-150 days before harvest. (CONTINUED ON PAGE 44) FIGURE 1. Small (300 m2) earthen fish pond used to evaluate fertilization and feeding combinations for Nile tilapia culture in Cambodia.
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