Mortalities Among Developing Trout and Salmon Ova Following Shock by Direct-Current Electrical Fishing Gear

Abstract

Two units of direct-current fishing gear, providing terminal potentials of 550 and 150 volts, were used to give shocks of different severities to trout and salmon ova in various stages of development. The purpose of the tests was to establish precautionary measures to prevent damaging eggs when using similar apparatus, in waters of similar conductivity, in the vicinity of natural redds containing live eggs. High terminal voltage caused heavy losses among pre-eyed eggs, considerably fewer losses among eyed eggs, and no losses to eggs that were near hatching. There were no losses among eyed or pre-eyed eggs with low terminal voltage. Eggs that had been buried in the gravel of a stream apparently received some protection from electric shock. Salmon alevins were killed by prolonged severe shock, but not by a similar shock of shorter duration. The alevins showed greatly increased activity and swam about sporadically when in the electric field, but did not exhibit galvanotropic responses of a directional character.