WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2019 45 The fishery for Nile perch Lates niloticus has been one of the most economically viable fisheries of Lake Victoria since introduction of the species in the 1950s (Cowx et al. 2003). The main aim of the introduction was to convert native bony haplochromines in the lake into more economically useful biomass for food and trade (Goudswaard et al. 2008). The value of Nile perch at the beach level is estimated to be more than US$400 million, with an export value of US$240 million (World Bank 2010). The contribution of Lake Victoria fisheries to the GDP of the riparian countries is Kenya 2.0 percent, Tanzania 2.8 percent and Uganda 3.0 percent, of which 78 percent is contributed by Nile perch (LVFO 2013). By 2012, there were 4,156 fishing boats operating on the Kenyan side of Lake Victoria, of which 3,240 were mainly targeting Nile perch (LVFO 2012). Due to the economic viability of Nile perch, the catch per unit effort in Lake Victoria has been progressively declining. The decline of the Nile perch fishery has been accelerated by various ecological challenges that have occurred in the lake (Ogello et al. 2013). Other perches, such as Eurasian perch Perca fluviatilis, Asian sea bass/barramundi Lates calcarifer and yellow perch Perca flavescens have been cultured successfully in Spain, some Asian countries and the USA, respectively (Acerete et al. 2004, Paterson et al. 2003). However, successful captive breeding and culture trials of Nile perch are scanty in the Lake Victoria region, despite the importance of Nile perch to the economies of the riparian countries. Although culture trials at the Kajjansi Aquaculture Research and Development Centre in Uganda demonstrated that Nile perch grows exponentially from 10 to 550 g in seven months (Gregory 2006), more data are needed across the East African region to authenticate the culture potential of Nile perch. Indeed, with the deteriorating ecological conditions of Lake Victoria, there is need for other alternatives of Nile perch production to ensure a steady supply to fish markets. Culture Trials of Nile Perch Juveniles in Cages and Earthen Ponds N.O. Outa and E.O. Ogello This article describes a study to generate data on handling, transport, feeding and captive culture of Nile perch to bridge some knowledge gaps in evaluating the aquaculture potential of this economically important fish. Study Area Fish were sampled around Winam Gulf (0° 15’ S, 4° 35’ E) (Fig. 1). The Gulf stretches about 100 km east to west and 50 km north to south and has about 550 km of shoreline. The Gulf is rather shallow, with an average depth of 6 m and a maximum depth of 37 m (Okely et al. 2010). Surface water temperatures range between 23.5 and 29.0 C. The area is sheltered from strong winds and serves as the breeding zone for many fish, including Nile perch (Campbell et al. 2003). Density during Transport Fish were obtained from Asembo Bay, Dunga, Kendu Bay, Homa Bay and Mbita beaches around Lake Victoria using beach seines (<10-mm mesh). Fish were sorted by size and stocked into hapa nets, each measuring 3 m × 3 m × 1 m, placed under papyrus shade near the lakeshore overnight, about 12 hours. This was meant to enable the fish to evacuate gut contents before transportation. Fish were packed into 10-L polyethylene bags containing 5 L of lake water at densities of 40, 80 and 100 g/L. Bags were oxygenated with medical-grade oxygen from a compressed gas cylinder to 100 percent saturation. Each density was replicated in three bags. Packed bags were placed in a plastic tank (1 m × 0.8 m × 0.35 m) lined all-round with a mattress to maintain the temperature at 25 ± 1 C, which was loaded into an air-conditioned automobile. Fish were transported by road for four hours from Homa Bay (0° 31’ S, 34° 27’ E) to the Kenya Marine and Fisheries Research Institute, Kegati station (0° 41’ S, 34° 46’ E). FIGURE 1. Map of Winam Gulf, Lake Victoria, Kenya: the red stars represent beaches where sampling was done during the experiment. The fishery for Nile perch Lates niloticus has been one of the most economically viable fisheries of Lake Victoria since introduction of the species in the 1950s. The catch per unit effort in the lake has been progressively declining, accelerated by various ecological challenges that have occurred. With the deteriorating ecological conditions, there is need for other alternatives of Nile perch production to ensure a steady supply to fish markets. (TEXT CONTINUED ON PAGE 46)
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