string: In the following species there are four or more haemoglobin components but they always can be divided into just two groups having different functional properties: the rainbow trout (Oncorhynchus mykiss, Salmonidae) (Binotti et al., 1971); the sockeye salmon (Oncorhynchus nerka) (Sauer and Harrington, 1988); a catostomid (Catostornus clarkii, Catostomidae) (Powers, 1974); the tench (Tinca tinca, Cyprinidae) (Jensen and Weber, 1982); an anostomid (Leporinus friderice, Anostomidae) (Peterson et al., 1989); a catfish (Pterygoplichthys pardalis, Loricariidae) (Brunori et al., 1979); the dogfish (Squalus acanthias, Squalidae) (Weber et al., 1983); and a species of sea chub ( Girella tricuspidata, Kyphosidae) (Wells et al., 1984).