Condition and pyloric caeca as indicators of food web effects in fish living in metal-contaminated lakes

Variations in fish condition, pyloric caeca (PC) mass and tissue metal concentrations were examined in two consecutive summers in yellow perch collected along two polymetallic gradients in Canada, Sudbury (ON) and Rouyn-Noranda (QC). The potential of PC mass variations to help interpret food web-mediated changes in condition was also evaluated. The lack of relationships between PC weight and condition, even in reference lakes, indicated that factors other than feeding rate influenced fish condition. Inter-annual variations in fish condition (12–58%), PC weight (14–20%) and tissue metal concentrations (30–550%) were often of greater magnitude than differences between reference and contaminated fish sampled in the same year. The apparent lack of correspondence between feeding rate and condition and the large inter-annual variation in examined metrics highlight the need to better understand the ecological underpinnings that influence metal toxicity in field situations.