Effects of Sublethal Exposure to Cadmium on Shelter-Seeking Behavior of Juvenile Orconectes rusticus (Girard) Crayfish

Abstract

Sublethal behavioral effects of heavy metals on crayfishes may adversely affect their survival in the environment. They may experience increased predation due to changes in their ability to remain in or under shelter. The effect of sublethal cadmium exposure on the ability of juvenile Orconectes rusticus crayfish to remain in shelter was evaluated. Four different treatment groups were used (N=12 juveniles each): a control group not exposed to cadmium, and three experimental groups exposed to 1, 2, or 3 mg Cd/L for 7 days. Crayfish were placed, individually, into small glass aquaria containing 3L of laboratory water, with continuous aeration. Each crayfish was provided with a dark, thigmotactic shelter. Cadmium was introduced into the aquaria on days 1 and 4 to establish and maintain the nominal concentrations. On days 5 through 7, observations were taken on each crayfish five times per day, with a minimum of 30 minutes between observations (15 observations per crayfish). The locations of the animals were recorded as in cover or in the open area of an aquarium. Repeated measures ANOVA was used to examine the effects of sublethal exposure to cadmium on shelter use by the juveniles. Juveniles in the control groups were in the shelters for 92.7% of the observations. Results from the experimental groups indicate a significant decrease in shelter use compared to the control group, suggesting hyperactivity induced by the cadmium exposure. Over the 3 days of observations, those in the 1,2, and 3 mg Cd/L exposure groups used the shelters 57.7%, 56.3%, and 32.0%, respectively, indicating hyperactivity induced by cadmium exposure. Looking at the daily results, those juveniles in the 1 mg Cd/L group increased shelter use from 52.0% to 64.0%, then decreased to 57.0%, while those in the 2 mg Cd/L group increased shelter use from 45.0% to 79.0% of the observations by day 3 of the observations indicating some habituation to the cadmium or recovery from the cadmium exposure. Those in the 3 mg Cd/L group spent progressively less time in shelter over the 3 days of observation, from 39.0% to 25.0% then to 32.0% by the third day, indicating sustained hyperactivity due to the sublethal cadmium exposure.