Rudd (1954), was the first scientist to study the physiology of icefish after reports that whalers had discovered three species of fish that had “colourless blood” (Figure 5). No blood pigments were found in samples of the three species, and after more detailed analysis of Chaenocephalus aceratus, an average of 0.77% of oxygen by blood volume was recorded. In comparison, two Norwegian species of fish (Notothenia rossi marmorata and Notothenia coriiceps), had mean values of 5.99% and 6.24% respectively (Rudd, 1954). Therefore, the conclusion was reached that C. aceratus did not have a method to take up oxygen in the blood, except by physical solution. Further evidence that C. aceratus lacked haemoglobin was that blood from samples contained less than 1mgm (milligram) of percentage iron, compared to mean values of 19.6-26.7 mgm in other fish species (Rudd, 1954). While Rudd was able to suggest that because the waters around Antarctic are “well aerated”, and that this may present a reason for the lack of haemoglobin, he was unable to ascertain the true cause of this loss of function and any potential benefits that it may have.
Figure 5. The lack of haemoglobin and red cells is a distinguishing characteristic of icefish. The two tubes contain blood drawn from a haemoglobin-expressing notothenioid fish (Notothenia coriiceps) on the left and a haemoglobinless Antarctic icefish (Chaenocephalus aceratus) on the right (Sidell and O’Brien, 2006).