Bichirs

Polypterus

“if I had discovered only this species in Egypt, it would compensate me for the pains usually involved in a long journey”. According to scientist Geoffry Saint Hilaire, who in 1798 took part in a scientific expedition organized by Napoleon to the mysterious and closed Egypt.

Sitting along the Nile, he discovered a meter-long primeval fish, which was already known to the Egyptians from the time of the Pharaohs. The locals called the fish something like Bee-sheer, which the French may have phonetically spelled Bichir in their own way. In 1902 the species was given the scientific name Polypterus bichir. The find was of great scientific significance.

Today’s primeval fish Polypteridae are the only survivors of the group Polypteriformes. Its origins go back to the late Cretaceous period, from 100-60 million years ago, known as the last phase in which dinosaurs flourished. Polypteriformes occurred in the area that now includes Africa and South America.

Today’s Polypteridae (Bichir’s) are among the most primitive ray-finned species still in existence. They all occur in freshwater areas in Africa, most of them up to about 10 degrees north and 10 degrees south of the equator. A fossil find of the modern Polypteridae in Chaad indicates that the species as we know it today already existed in the late Miocene (5.3 million years ago). The fossil (appropriately named Polypterus faraou) bears close resemblance to Polypterus bichir and Polypterus endlicheri, two species still found there.

Evolution does not seem to take place very quickly in these primeval fish. Nevertheless, due to the large geographical spread and different habitats, various species and variants have arisen: The family itself consists of two genera.

Erpetochthys (with only one species: Erpetochthys calabaricus).
Polypterus consists of 13 species and a number of variants within them.

In recent decades, much confusion has arisen among ichthyologists about the species classification and how the later discovered variants should fit into it. Substantial changes have recently been made to the species classification due to a change in insight. A distinction is now made into three main groups of Polypterus:

The Senegalus group including Erpetoichthys. These upper jaw types have a longer upper jaw than the lower jaw or at least of equal length. The mouth opens downwards, so that they are better equipped to eat (dead) food lying on the bottom. The maxillary group consists of E. calabaricus, P. senegalus, P. palmas, P. delhezi, and P. polli.
The Weeksii group. Also an upper jaw type with a longer or minimally equal upper jaw than the lower jaw. This group includes P. weeksii, P. ornatipinnis, P. retropinnis, P. teugelsi and P. mokelembembe
The Bichir and Endlicheri group with a lower jaw longer than the upper jaw, so that the mouth opens upwards. This makes them more specialized in hunting live animals, such as amphibians, aquatic insects, and fish. This group includes P. bichir, P. ansorgii and P. endlicheri. Lower jaw types tend to be a lot larger than the upper jaw types.

The fish

Bichirs have a cylindrical elongated body, resembling that of a reptile. It is equipped with scale armor and 7 to 16 separate triangular dorsal fins (Polyperus means many-finned), which gives the fish a dragon-like appearance. The pectoral fins are exactly where you would expect the legs to be in a lizard. The swim bladder evolved into a primitive lung, which also allows the fish to use air from the surface. Combined with the gills, they can survive in the low-oxygen conditions of warm swamp areas and even out of the water for a while. Even if the oxygen content in the water is sufficient, they will regularly swim to the surface for a mouthful of air. Juveniles have clearly visible external gills, like salamanders. In most specimens, these disappear at a later age. The skin is covered with a strong scale armor. The scales are triangular, with a hook at the end, and covered with a hard and tough material that also prevents water loss outside the water.

Polypterus has poor eyesight and a highly developed sense of smell. It follows scent trails to find food. For this, they are equipped with tubular nasal openings. Polypterus can survive out of water for several hours, and in humid conditions for up to 2 days. The fish then propels itself over land with its pectoral fins.

Prey are slowly stalked and swallowed up close. Bichirs have two plate-like bony structures in the lower jaw that help them chew food. In nature, when eating carrion, the fish has been observed to rotate on its axis to tear off chunks of flesh (much like crocodiles do).