Partial substitution of balanced feed by Chaya leaves in Nile tilapia production: a bioeconomic analysis

Tilapia culture in Yucatan State, Mexico, is largely semi-intensive. The producers are mostly poor farmers who receive government subsidies for purchase of fingerlings and balanced feed. Feeding practices are often inadequate (satiety rations), moreover, producers frequently suffer financial and resource shortfalls. During feed shortages producers are known to use empirical application of chaya (Cnidoscolus chayamansa) leaves, used traditionally in human and animal nutrition. A study was done of growth in juvenile tilapia using diets containing balanced feed with chaya (25 and 50% of substitution), complete, half-complete and satiety rations of balanced feed, during the warm season. The results were used to develop a bioeconomic model and implemented in MS Excel program, with a one-day time step. In order to minimize the cost of tilapia feeding, and maximize the benefits by using a limited amount of balanced feed per cycle. In addition the analysis was completed using the Marginal Rate of Technical Substitution (MRTS). According to results from MRTS, it is necessary to add 2.51-3.91 units of chaya for each reduced unit of balanced feed, to maintain the same level of production. In a resource limited situation, substitution of 50% of balanced feed for raw chaya leaves generates a harvest size greater than complete and satiety rations of 24.8 and 28.8% respectively. When considering sale prices that are consistent with size at harvest and costs, treatments with chaya considerably maximized profits

Bioeconomic analysis of ration size in intensive tilapia culture

Balanced feed represents approximately 60 % of production costs in fish culture and ration size has significant effects on this parameter. Ration size varies according to culture strategies and producer knowledge. It can also have environmental implications since feed can be a pollutant. A bioeconomic model was developed for an intensive system with recirculation considering different ration sizes (100 % recommended levels, 80 %, 50 % and satiety). Assumptions for model parameterization were based on previous production experiments and market factors in Mexico. The 80 % ration resulted in the greatest reduction in water changes, energy and operating capital, and was profitable. The 50 % and satiety rations were not profitable, and the latter had the highest water change and operating capital requirements