Fisherman, Beware

Fresh-water fishermen had better be careful how they use DDT. If they wipe out mosquitoes by treating the breeding places, they may starve the neighborhood fish by cutting off their food supply. That's the opinion of Professor Bertil G. Anderson, who teaches at both Ohio State and West Virginia. He has been studying the effects of DDT on living fish food, and he is alarmed.

The game fish are the topmost rung of a long fish-eat-fish biological ladder. At the bottom are one-celled organisms--bacteria, algae, protozoa--which form the prey of slightly larger creatures (tiny crustaceans). These get eaten by the next size creatures--and so on up the line.

A vital link in the chain of eaters and eaten are daphnia, or water fleas. These swarming, near-microscopic relatives of crabs and lobsters are the staff of life for many other aquatic species, which are ultimately the food of fish. But if DDT gets into their water, it knocks the daphnia cold. A single pound of DDT in a 38-acre pond averaging ten feet in depth, warns Professor Anderson, is enough to kill the daphnia--and thus eventually starve the fish.

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