Mercury Feeding Schedules: Effects on Accumulation, Retention, and Behavior in Trout

Abstract

Rainbow trout (Salmo gairdneri) were exposed to 0.5 and 2.0 gg/g doses of ethyl-mercury (ptoluene sulfonanilide) "Ceresan" each day for a full year and 2.5 and 10 gg/g doses delivered every 5th day of feeding during the year. A further study extended dose levels from 5.0 to 25.0 gg/g Ceresan given daily. Exposure to the lower doses of mercury for either feeding schedule led to concentrations of mercury in muscle that were similar (regression slope equaled one) to the average daily index of dose for as long as 6 months of feeding. Assessment of concentration in muscle at 9 months of feeding showed a breakdown of the effect in all groups except the one receiving 0.5 gg/g of Ceresan daily. Both dose level and schedules influenced the concentrations of mercury in muscle. Daily treatment with higher doses, e.g., 5.0 through 25.0 gg/g, led to dose-related concentrations of mercury in muscle but the regression was greater than one. Orders of mercury concentration in a variety of other tissues differed significantly and were generally related to dose. Fish receiving 10.0 gg/g of mercury every 5 days or 5.0 gg/g or greater doses every day in their feed were unable, with few exceptions, to learn to avoid shock when preceded by a signal-light. But beyond performance on the learning task, there was no evidence of impairment of general behavior nor was there any indication of physical debilitation resulting from any treatment. There appeared to be a fairly rapid loss of mercury from selected tissues, although estimates of total body burden of mercury remained high after 6 months of mercury-free feeding. Interest in the clinical and lethal effects of mercurials has led to a number of excellent investigations into the absorption, retention, and distribution of several mercury compounds in humans and experimental animals (Berlin 1963; Brown 1954; Forney and Harger 1950). The results of these studies are similar. General debilitation is associ-

Mercury effects on predator avoidance behavior of a forage fish, golden shiner (Notemigonus crysoleucas)

“…This increased activity was inversely proportional to survival against grass shrimp ( Palaemonetes pugio ) predators. Rainbow trout fed 10 μg Hg/g every 5 d were unusually nervous, showing aimless movement or agitation [37]. Largemouth bass ( Micropterus salmoides ) were also hyperactive after exposure to 10 μg/L Hg for 24 h [16].…”

The effect of mercury on the feeding behavior of fathead minnows (Pimephales promelas)

“…After successful training, the treatment fish were exposed to Hg and retested. These studies reported impaired retention at waterborne exposures of 3 µg/L and 6 µg/L HgCL 2 using goldfish (Weir and Hine, 1970), and at body levels greater than 2.85 µg/g using rainbow trout (Hartman, 1978). In an operant conditioning test (target strikes with food as reinforcement) involving goldfish, Salzinger (1973) reported impaired retention at 6…”

“…In a number of early investigations, fish were trained with classical conditioning techniques to show a light avoidance response, and then exposed to a toxicant. Weir and Hine (1970) (Hartman, 1978) and retention (Salzinger et al, 1973).…”

Methyl mercury induced visual deficits in rainbow trout

“…Post et al (1973) found that rats required more trials to learn a T-maze after oral administration of MEHG. Hartman (1978) reported that trout in the highest dose group were not able to acquire an avoidance response to shock. The results of the present study show that MEHG did not influence the number of trials for trout to achieve the 90% response criterion and therefore did not affect the memory facility of trout.…”