Kafue bream

The Kafue bream is an important food fish in Rhodesia, and its vulnerability to insecticides makes it a concrete example of the costs that chemical mosquito control can impose on local food supplies. Its young can be killed by very low concentrations of DDT in shallow pools—the same kinds of waters that favor mosquito breeding—leaving the conflict between mosquito control and fish conservation unresolved.

Food fish and vulnerable young

The book identifies the Kafue bream as an important food fish in Rhodesia, where fish cultivated in ponds can provide an indispensable source of food. Its young are especially vulnerable: exposure to just 0.04 parts per million of DDT in shallow pools can kill them, and even smaller doses of many other insecticides may be lethal.

The mosquito-control conflict

The shallow waters where the young fish live are also favorable breeding places for mosquitoes. That overlap makes insecticide use more than a question of controlling pests: chemicals applied without regard for their effects on fish threaten a food resource in the very habitat where mosquito control is directed. The book presents the problem of controlling mosquitoes while conserving the Kafue bream as one that has not been satisfactorily solved.

Significance

The Kafue bream’s example brings the consequences of insecticide use into focus through a specific species, habitat, and lethal concentration. It also makes visible a tension that broad spraying can obscure: the immediate aim of suppressing mosquitoes may conflict with the survival of fish on which people depend for food.