Selective cropping of the dam may be useful in some cases, but more often it is a mistake toremove only the large fishes. This is particularly so in small dams but it is not so important in larger dams.
In most dams, it is advisable to remove fishes of all sizes – especially in waters where undesirable species occur. For this the most effective gear is a seine or drag net. In small dams anet 30 – 45 m long, 1 -1.5m deep, tapering at the ends may be convenient to use, but in larger dams a net 45 – 60m long 35- 40m deep and tapering in the wings to 1.5 – 1.8m will be more effective. The mesh size in both cases should be 50mm in wings and 25 – 35mm in the centre (⅓ of the net in the middle).As previously mentioned, efficient seine netting requires a smooth weed-and-obstruction-free area for fishing and a boat is usually required. Only in small dams can seine fishing be done with the help of long ropes from the shore without a boat.
Gill nets are valuable in larger dams where seine netting is not possible or can only be done to a very small extent. Gill nets are selective and therefore for balanced fishing anumber of nets of different mesh sizes should be used.
The value of traps and fishing with rod and line should not be underestimated. Where traps and reed baskets can at certain times of the year be properly used, they yield surprisingly high catches and considering they are inexpensive and simple in their design, their use should play a greater part in fish farming than at present.
Rod and line are used more for pleasure and recreation than for gain, but the fisherman with a hook can often be very useful in removing small undesirable species offorage fish from a dam.
Yields from farm dams may vary considerably and depend to a large degree on the management of the dam and the fishing effort. As a maize crop may vary from 1 tonne per ha to 10 tonne per ha, so the fish crop may also vary from 25kg up to 1 000kg/ha. Smaller dams up to 8ha usually give higher yields.