WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2014 19 In Yucatán, Mexico, aquaculture is not a common practice. In 2001, in the framework of a national program toward poverty alleviation, a project was launched through which 118 circular 10-m diameter concrete fish culture tanks were constructed on smallholders’ lands (Fig. 1), estimating that each tank would give work, food and income to 10 farmers. The objective was to fight poverty by promoting aquaculture of Nile tilapia Oreochromis niloticus, foster tilapia consumption and commercialization, and use discarded tank water to irrigate crops around tanks, such as corn, pumpkin, beans, chili peppers and a variety of fruits. Although the Yucatán rural population perceives fish culture as an activity compatible with their agriculture production and as a potential source of food and income, only five tanks were in operation by 2008. The high cost of commercial feeds is one of the main problems limiting fish culture development in the region. Periphyton — the microalgae, bacteria, detritus and small animals that attach and grow on hard surfaces submerged in water — might provide a solution to this constraint and allow reactivation of tilapia culture in existing tanks. The installation of substrates in the water column to promote the development of periphyton as a natural food for Nile tilapia, a species capable of browsing on periphyton, a priori seems like an appropriate low-cost technology for small-scale tilapia culture in rural Yucatán. Periphyton-based systems with no additional feed supply have Limitations on Periphyton Productivity and Tilapia Growth from High Hardness and Alkalinity of Groundwater in Yucatán, Mexico Martha Hernández, Eucario Gasca-Leyva, David Valdés and Ana Milstein been used in tropical Africa and Asia as a traditional way of enhancing fisheries in coastal lagoons. Since the 1990s, this technology has been adapted to aquaculture ponds, allowing fish culture where feed inputs are scarce or unavailable. Substantial research on periphyton-based aquaculture has been performed since then and various aspects have been reviewed or summarized (van Dam et al. 2002, Azim et al. 2005, Uddin et al. 2007, Azim 2009, Saikia 2011, Milstein 2012, Milstein et al. 2013). In Yucatán, there is no previous experience with periphyton-based aquaculture; thus, our first step was to test periphyton growth on cheap, locally abundant substrates: bamboo cane, stick of guano palm, corn cob, corn cane, plastic bottle, corn leaf, (Figs. 2 and 3). Guano stick resulted in the best periphyton growth and had better durability than other substrates. Several experiments on tilapia growth were carried out in static tanks filled with ground water, most of them outdoor and without aeration or water renewal to simulate the conditions in farmers’ tanks (Fig. 3). Treatments were tanks ‘with’ and ‘without’ substrates. Guano sticks and plastic bottles provided an underwater hard surface area equivalent to 80 percent of the tank surface area. Under inorganic fertilization without fish feed inputs, in tanks with guano sticks, tilapia weight and biomass at harvest were significantly less than in tanks without substrates. ABOVE, FIGURE 1. Concrete culture tanks on a fish farm in Yucatán, Mexico. (Photo: Martha Hernandez) The high cost of commercial feeds is one of the main problems limiting fish culture development in the region. Periphyton — the microalgae, bacteria, detritus and small animals that attach and grow on hard surfaces submerged in water — might provide a solution to this constraint and allow reactivation of tilapia culture in existing tanks. The installation of substrates in the water column to promote the development of periphyton as a natural food for Nile tilapia, a species capable of browsing on periphyton, a priori seems like an appropriate low-cost technology for smallscale tilapia culture in rural Yucatán. (CONTINUED ON PAGE 20)
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