Experimental Polyculture of Milkfish ( Chanos chanos) and Mullet (Mugil cephalus) Using Earthen Ponds in Kenya

Abstract—Seasonal growth of milkfish ( Chanos chanos ) and mullet ( Mugil cephalus) was studied in polyculture in six small earthen ponds in Mtwapa Creek and Gazi Bay, Kenya, between 2005 and 2006. The ponds were sited on sandy mangrove flats and were periodically connected with the sea providing water exchange during high spring tides. This inundation also filled mangrove pools and channels where fish fingerlings and juveniles were seined with push nets to establish their seasonal abundance and to stock the ponds. Fingerlings weighing 5-9 g were stocked at 4 fish/m 2 and a polyculture ratio of 5 milkfish: 1 mullet. The ponds were fertilized with dry chicken manure at 15 kg/pond every two weeks (0.595 g/m 2 per day). Fish were sampled monthly, basic water quality parameters (temperature and oxygen) were monitored weekly and nutrient analysis four times per crop. There were significant differences in milkfish and mullet abundance between months (p <0.05). Milkfish growth rate was significantly different between the wet (0.52±0.18 g/day) and dry (1.21±1.0 g/day) seasons (P <0.05), as was that of mullet (0.15±0.04 and 0.29±0.15 g/day, respectively; P <0.05). The production of mullet fish was 160-380 kg/ha and milkfish 1 440–5 160 kg/ha. Fish survival varied between 81.4% in the wet season and 90.3 % in the dry for milkfish and 79.8–87.0 % for mullet. Water quality parameters fell within the culture requirements in both the wet and dry season, with chl-a, and salinity being significantly higher in the dry season, while phosphates and nitrites were significantly lower in the dry season (p <0.05).  Keywords: polyculture, milkfish, mullet, earthen ponds.