WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2019 47 the culture period in and out of the cages. The average water quality parameters before the culture experiment were 0.36±0.14, 0.29±0.16, 0.53±0.03 and 0.16±0.01 for NH4, NO2, NO3 and PO4 respectively. Water quality was not different between the open lake and the fish cages as well as before and during culture (Table 2). Discussion Aquaculture can help improve food security in Kenya. This depends on research and scientific knowledge available on the fish considered for culture. Nile perch has been considered as an unconventional aquaculture fish (Kigbu et al. 2014) and its culture has not been practiced, particularly in Kenya. Knowledge of the feeding behaviour of fish is important to formulate feeds during culture in captivity. Nile perch is a predatory fish that feeds predominately on fish and shrimp (Kishe-Machumu et al. 2012, Dadebo et al. 2005, Mhitu and Chande 2004). Successful and economical handling and transportation of fish fingerlings from the source to the culture centres or facilities is important in the fish production chain (Bui et al. 2012). Any fish for aquaculture should be able to withstand handling stress during sampling and transport (Acerete et al. 2004). Transport experiments have been conducted for most of the important aquaculture species in Kenya like Labeo victorianus, Oreochromis niloticus and Clarias gariepinus (Orina et al. 2014, Oyoo-okoth et al. 2011) but not for Nile perch because this species has not been transported and cultured effectively. This study demonstrated that Nile perch can withstand handling and transport, indicating the capacity of Nile perch to quickly adapt to packing conditions. Because of the lack of data on optimal packing densities, handling and transport of Nile perch, mortality related to cannibalism and transport stress was a challenge during preliminary transport experiments. The procedure of fish handling is important in determining the stress level during packaging for transport. To reduce stress, fish were scooped before the net was hauled into the boat and transferred to a basin for sorting and packing. Because Nile perch is highly piscivorous, size sorting is necessary before packing to reduce cannibalism inside transport bags. Fast growth is a desirable characteristic in any fish considered for aquaculture (Maithya et al. 2003). Culture methods and systems should therefore be designed to encourage and promote fast growth. Fish growth is affected by diet, water quality and handling stress. Water quality challenges experienced in pond systems are reduced in cages due to the constant flushing of wastes and remnants of feed by water currents. This encourages faster growth in fish reared in cages compared to pond environments (Huchette and Beveridge 2003). Mwachiro et al. (2012) recorded a significantly higher growth rates in Oreochromis jipe reared in cages in Lake Jipe than in ponds. They attributed this to the higher dissolved oxygen in the cage due to water currents and the better water quality compared to conditions in ponds. Cage aquaculture in Kenya is at its formative stages and there is very little technical support to farmers venturing into this culture method. In the current study, the size of fish at the end of culture period was homogenous with few smaller Nile perch. The problem faced in culture of Nile perch is the predatory nature since it preys on live fish (Outa et al. 2016). Trial experiments in Uganda showed considerable potential for aquaculture. The most promising results were obtained from raising the fish in trash-fish fed net cages sited in ponds. The growth of wild-caught Nile perch TABLE 2. Ranges and averages (in parentheses) of water quality parameters in the open lake and Nile perch cage during the culture period. Parameters Open water Inside the cage (mg/L) TAN 0.29 - 0.40 (0.30±0.04). 0.31- 0.41 (0.35±0.04) NO2 0.33 - 0.42 (0.37±0.05) 0.29 - 0.41 (0.36±0.05) NO3 0.51- 0.61 (0.57±0.04) 0.49 - 0.60 (0.56±0.04) PO4 0.16 - 0.20 (0.17±0.01) 0.16 - 0.19 (0.17±0.02) FIGURE 3. Monthly growth rate of Nile perch in cages and ponds. Nile perch has been considered as an unconventional aquaculture fish and its culture has not been practiced, particularly in Kenya. This study demonstrated that Nile perch can withstand handling and transport, indicating the capacity of Nile perch to quickly adapt to packing conditions. The growth rate of Nile perch in cages was significantly greater than that in ponds. (TEXT CONTINUED ON PAGE 48)
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