Gillnets and castnets are the major gear used to harvest Tilapia commercially in Kainji Lake. The gillnets are used in two ways, passive and active netting. Aspects of these three methods of fishing are discussed below. Illicit poisoning is a problem in the lake.
The gillnets are set late in the day and picked up early in the morning. The catch of Tilapia in passive gillnets is incidental to the catch of other species, and probably relatively few are taken this way. As noted previously many thousands of yards of survey gillnet were set between 1969–1972 and only about 500 Tilapia were captured.
The survey gillnets and most of the commercial nets used in the lake are multifilament nylon. Taylor and Denyoh (n.d.) found that experimental monofilament nylon nets caught 4.5 times as many T. galilaea in Volta Lake as did the same mesh size of multifilament nylon nets. They note that commercial fishermen who observed the comparative catches subsequently converted from multifilament to monofilament nets. Monofilament nets were found to disentangle from trees more easily than multifilament nets. Counterbalancing this is the greater initial cost of monofilament, and the greater rapidity with which these disintegrate when left in the sun.
Shallow nets of 5 to 7-inch stretched mesh without a leadline and with floats about 15 feet apart are quietly set after dark near known Tilapia habitat. The nets are set in 3 to 6 foot deep water about 15 to 45 feet offshore, and parallel to the shoreline. Then the boat proceeds with much splashing and noise between the shoreline and the net, and the fish are frightened into the net. The net is then picked up, leaving the fish little opportunity to work itself free of the meshes. One attempt to fish this way, observed by the expert near Monai, caught two T. galilaea (200 and 240 mm S.L) in a 6-inch mesh net. The fisherman reported that when active gillnetting was first taking place in the lake two years previously much larger T. galilaea were caught and the use of 7-inch mesh nets was profitable, but that fewer and smaller fish were now available.
Castnets of stretched mesh size from 1 to 6-inch are used at various times of the year. Smaller mesh nets are used during highwater levels among flooded vegetation and aquatic weeds. The reaction of Tilapia to castnets is to dive into aquatic vegetation and so escape the fishermen as the net rests on top of the grass. Larger mesh and indeed castnetting generally, is most profitable when the water level is down, the fish are more concentrated in the reservoir, and there is less brush and vegetation to impede the net.
Two fishermen comprise a boat crew, one for propulsion in the stern, the other standing in the bow to spot fish by water movements and to cast the net. The largest number of Tilapia observed by the expert to be caught in one cast consisted of eight small T. galilaea (about 180 mm S.L.) in a 3 inch stretched mesh castnet.
Tilapia are not a favourite fish among local Nigerians, as most of their fish for market are smoked and Tilapia dries out too much. An oilier fish such as Citharinus or catfish is preferred. Shagunu-based fishermen claim that both T. galilaea and T. nilotica are good when fried, but that T. nilotica is ‘sweeter’ (better flavoured) when used in soup.
A poll of European taste preferences at the Shagunu research station indicated that, among the Kainji Lake fish, the Nile perch Lates niloticus was first choice followed closely by T. galilaea and T. nilotica. They noted that Tilapia develop a marked ‘muddy’ taste when Microcystus algae became noticeable in the lake; this taste could be partly removed by overnight soaking in water or milk.
