In the first part of this study, metal bioaccumulation and metallothioneins were investigated in various organs of the red‐blooded teleost,Trematomus bernacchii,and the haemoglobinlessChionodraco hamatus.Hepatic metallothionein correlated positively with Cd, Cu, and Zn concentrations inT. bernacchii,whereas inC. hamatusit showed a positive correlation only with Cd. A metal‐linking protein with characteristics typical of metallothioneins was identified in the liver ofC. hamatusas well as ofT. bernacchii.In the second part, data on the amino acid sequence of the enzyme Superoxide dismutase (SOD) were analysed and compared with SOD sequences from other animals. In the third part, a low degree of tolerance against the toxic effects of copper was recorded in two cilates,Pleuronema coronatumandEuplotes rariseta,collected from Terra Nova Bay and cultured in the laboratory.