() How do juvenile yellow perch respond to dietary and waterborne Cd under natural field conditions?
Kraemer, L.1, Campbell, P.1, Hare, L.1, 1 INRS-ETE, University of Quebec, Ste Foy, Quebec, Canada
ABSTRACT- The objective of this field study was to determine the relative importance of water and food as Cd sources for juvenile yellow perch. The perch were caged within either a reference lake (L. Opasatica) or a Cd-contaminated lake (L. Dufault), both lakes being located in the Rouyn-Noranda area in north-western Quebec, Canada. The cages were designed to allow free exchange of water between the cages and the lakes, while restricting the movement of zooplankton. The fish were fed with zooplankton from either the reference or the Cd-contaminated lake, creating four treatment groups: reference; Cd-contaminated food only; Cd-contaminated water only; and Cd-contaminated food and water. In addition, uncaged indigenous perch from both lakes were sampled on days 0, 15 and 30. The gills, gastrointestinal tract (GIT), kidney and liver were sampled after 15 and 30 days of exposure and the tissues were measured for Cd. Results demonstrated that the gills, GIT and kidney were all influenced largely by aqueous Cd, while the liver appeared to respond to both dietary and aqueous Cd. To further examine Cd accumulation at the subcellular level, differential centrifugation was carried out on the liver, yielding fractions containing cellular debris, organelles, heat-denatured proteins and heat-stable proteins. In the reference treatment and indigenous Lake Opasatica fish, the majority of the (low) Cd burden was associated with organelles and heat-denatured proteins (metal-sensitive fractions, MSF), while in Lake Dufault fish the majority of (much higher) Cd burden was associated with the heat-stable protein fraction (metal-detoxified fraction, MDF). The MDF in fish exposed to contaminated food only, or contaminated water only, became increasing important as total hepatic Cd concentrations increased, indicating that metallothionein synthesis had been effectively induced within the first 30 days of exposure. The importance of both food and water as a Cd source in this field study suggests that models designed to predict Cd concentrations in yellow perch will be more reliable if they consider both dietary and waterborne Cd.
Key words: field study, dietary Cd, yellow perch, subcellular distribution