Effect of acute exposure to zinc on osmoregulation and water balance of the aquatic larvae of the blackfly Simulium ornatipes

Abstract

The effect of exposure to zinc on the osmoregulation and water balance of the aquatic larvae of the blackfly S. ornatipes was investigated using a weighing procedure. Changes in weight and water content of the haemolymph and body tissues of samples of larvae exposed to acute levels of zinc were measured. Larvae were also exposed to ouabain as this was expected to affect osmoregulation. Osmoregulatory ability was investigated by measuring the changes in weight of samples of larvae placed in various hyperosmotic solutions and in an ouabain solution. Performance of larvae exposed to sublethal levels of zinc was compared with that of controls.

Larvae dying from zinc exposure exhibited a substantial drop in haemolymph volume, but tissue fluid levels remained constant. Similar results were obtained after exposure to ouabain. Prior exposure to zinc did not affect the permeability of the body wall or its ability to absorb water. Recovery from osmotic stress and the ability to tolerate ouabain exposure was affected, however. It is suggested that the loss of weight shown by larvae dying from zinc exposure is due to excessive primary urine production leading to dehydration.