Assessment of tissue-specific accumulation and effects of cadmium in a marine fish fed contaminated commercially produced diet

Commercially produced fish diet is now widely used in fish farming but it often contains elevated levels of cadmium (Cd). However, the adverse effects on fish are poorly understood. In this study, farm-raised marine grunts, Terapon jarbua, were fed Cd-contaminated diet or exposed to waterborne Cd for 4 weeks. Tissue-specific Cd bioaccumulation and its effects were subsequently examined. We found that Cd was accumulated in different fish tissues (digestive tracts, gills or livers). At the end of the exposure, Cd accumulation peaked in the fishes’ livers (5.0–6.3 μg g−1), followed by the digestive tracts (0.83–3.16 μg g−1) and gills (0.27–2.74 μg g−1). Endpoints such as the survival rate, specific growth rate, condition factor, and superoxide dismutase activity were not significantly affected by Cd exposure. In contrast, metallothionein (MT) induction and subcellular Cd distribution indicated that there were possible sublethal effects of Cd exposure. MT was induced in response to Cd accumulation, but it returned to the control levels after a longer exposure period, except for hepatic MT induction resulting from waterborne or low dietary Cd exposure. The Cd percentage in the metallothionein-like protein (MTLP) fraction increased over exposure time, and it accounted for more than 57% Cd in the fishes’ livers and 80% Cd in their digestive tracts by the end of the exposure period. Overall, although Cd in commercial fish diet did not have significant lethality to T. jarbua, sensitive responses such as hepatic MT induction and subcellular Cd distribution revealed that the Cd-induced storage and detoxification in T. jarbua may increase fish's tolerance to toxic metals.