Lead-induced metabolic imbalances and feeding alterations in juvenile fathead minnows (Pimephales promelas)

Abstract

Contaminant-induced feeding pattern changes may be a consequence or cause of changes in internal energy stores. Juvenile fathead minnows (Pimephales promelas; 25 ± 3 mm standard length) were exposed to 0.0., 0.5 or 1.0 ppm lead (Pb) during a 2-week preexposure and 2-week testing period (4 weeks total exposure). Changes in prey size selectivity, satiation levels, defecation rates, and weight were recorded. When simultaneously offered two prey sizes (10 2-day-old and 10 7-day-old Daphnia magna) control fish began switching from larger, more difficult-to-capture 7-day-old daphnids to smaller, easier-to-catch 2-day-old prey [analysis of variance (ANOVA) p < 0.06] by day 3. Fish exposed to 0.5 ppm Pb displayed a significant switching (ANOVA, p < 0.06) by day 10. Fish exposed to 1.0 ppm Pb did not significantly change their preference for 7-day-old daphnids. After 2 weeks of Pb exposure, control fish ate more flake food and did not satiate as quickly as exposed groups (ANOVA, p < 0.05). Fish exposed to 1.0 ppm Pb displayed reductions in amount of food remaining by day 4; control and 0.5 ppm Pb-exposed fish displayed a steady decline in the amount of food remaining. Daily defecation rates of Pb-exposed fish were significantly higher than controls (ANOVA, p < 0.05). Although all groups gained weight, there was a significantly smaller increase in Pb-exposed groups (ANOVA, p < 0.05). By altering prey size choices and rate of switching to energetically less costly prey, increasing perseveration (i.e., repeated efforts to capture single prey item) and visuo/psychomotor difficulty, shortening feeding bouts, and increasing defecation rates, Pb may cause metabolic imbalances in juvenile fish.