One group of fish, the Channichthyidae, are peculiar in that their blood lacks haemoglobin. The mackerel icefish belongs to this group. The phenomenon is otherwise known only in the transparent eel larva (leptocephalus). This was unknown to science until the early 1950s, when the Norwegian whale scientist Johan T. Ruud began to look at what the whalers called “fish without blood”. At first, it was believed that they lacked red blood cells as such, but they do not.
Otherwise, many fish groups are represented in the Antarctic fauna, although in most cases, only by one or two species. Some of these, called “endemic species”, are found only in the Antarctic. These species are often difficult to identify on the basis of external characteristics alone, so their swim-bladders and otoliths (tiny stones in the ear) need to be checked in order to identify them accurately.
Squid
Antarctic squid vary widely in size, from the small, 15 cm-long Brachioteuthis species to the colossal 4m-long Mesonychoteuthis which, in addition to its suckers, has hooks on its arms that it uses to catch its prey.
Cuttlefish
The cuttlefish are less well known, and although they are very common, there are doubtless several species still unknown to science in the Antarctic ecosystem.
