W7 AM Acclimation / Adaptation of Animals to Metals: Resistance, Tolerance, and Cost
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 327-329

(CHO-1117-238003) Chronic exposure of rainbow trout to dietary cadmium: physiological responses and acclimation.

Chowdhury, M.¹, Pane, E.², Wood, C.³, ¹ US EPA-MED, Duluth, MN, U.S.A.² Monterey Bay Aquarium Research Institute, Moss Landing, CA, U.S.A.³ McMaster University, Hamilton, ON, Canada

ABSTRACT- Chronic effects of dietary metals in fish are not yet well defined. We examined a suite of physiological parameters (respiratory, acid-base, ionoregulatory, haematological, stress, and renal) in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 45 - 52 d. Blood sampling via an indwelling arterial catheter revealed that dietary Cd exposure had no major effects on blood gases, acid-base balance, and plasma ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-), but resulted in an increase in hematocrit (49 %) and hemoglobin (74 %) and a decrease in the plasma total ammonia (43%) and glucose (49%). Urine sampling via a urinary bladder catheter showed a significantly higher excretion rate of ions(Zn²⁺, K⁺, Na⁺, Cl^-), glucose and protein in Cd exposed trout relative to non-exposed naïve trout, with no changes in glomerular filtration rate (GFR) and urine flow rate (UFR). When both groups were challenged with waterborne Cd (10 g/L, ∼ 50% of the 96-h LC50) for 72 h, fish exposed to dietary Cd showed acclimation with increased protection against the effects of waterborne Cd on arterial blood P_aCO2 and pH, plasma ions and stress indices. After waterborne Cd challenge, plasma Ca²⁺ levels declined from the pre-challenge level, but the effect was more pronounced in non-acclimated fish (44 %) than in Cd-acclimated fish (14%) by 72 h. Similarly, plasma K⁺ and four traditional stress-parameters (plasma total ammonia, cortisol, glucose, and lactate) were elevated only in the non-acclimated fish. However, urinary loss of ions and protein, not glucose, remained elevated in the Cd pre-exposed trout during waterborne Cd challenge. Thus, chronic exposure to dietary Cd produces acclimation in trout with increased protection against additional stress caused by waterborne Cd. It appears that such acclimation also involves some physiological costs in terms of renal dysfunction and elevated urinary losses (Supported by NSERC, ICA, CDA, NiPERA, ILZRO, Teck-Cominco, Noranda-Falconbridge, & Inco).

Key words: Cadmium, Rainbow Trout, Diet, Acclimation