Phytoplankton productivity in newly dug fish ponds within Lake Victoria wetlands (Uganda)

The declining Lake Victoria fisheries resource led to a growing recognition of aquaculture as a source of livelihood to riparian communities. Finger ponds speculated to naturally stock fish during flooding and retain them during dry seasons were introduced within the lake’s wetlands. In order to develop a better understanding of these ponds’ dynamics, algal primary productivity was studied in eight newly dug wetland fishponds (8 x 24 m) located in two villages along the northern shores of Lake Victoria (Uganda) before stocking them with fish. Gross primary productivity was low for both sites ranging between 0.00 and 2.63 mg O2 L-1 h-1. The net areal primary productivity of Gaba ponds ranged from -0.34 to 4.66 mg O2 m-2 d-1 while that of Walukuba ponds ranged from 1.16 to 6.25 mg O2 m-2 d-1. Chlorophyll a mean values were 23.46 ± 12.50 ìg L-1 and 75.56 ± 44.35 ìg L-1 and mean turbidity ranges were 132.1 –242.25 and 432.54 - 158.49 NTU for Gaba and Walukuba ponds respectively. Reduced light supply due to the high inorganic turbidity may have been the main limitation for photoautotrophic primary productivity and ponds potential fish yield of 10 - 24 kg ha-1 fish per year