The effects of lapsed time since feeding upon the toxicity of zinc to fish.

This study was undertaken to determine the effects of elapsed time from feeding to exposure upon the tolerance of goldfish (carassiu auratus l.) to zinc. Methods followed those in the 24 hour static bioassay of the Ohio River Valley Water Sanitation Commission (SMITH et al., 1973). Fish were fed for 25 minutes and at specific times after feeding (0, 1, 2, 4, 6, 12, 24, 72 hours) groups of 10 fish were placed into 18 liters of water containing a lethal concentration (100 mg/l) of zinc as ZnSO4. Time until death was recorded for individual fish. A total of 420 fish (excluding controls) were exposed to zinc in the course of seven experimental runs. Statistical analysis revealed a slight but non-significant increase in survival time as the interval between feeding and exposure to zinc increased. These variations in survival time do not appear to be of sufficient magnitude to support the standard acute bioassay requirement that fish not be fed for 24 or 48 hours prior to their exposure to a toxicant.