• Species: Lung fish

  • Species: Lung fish

  • Species: Lung fish

  • Species: Polypterus ornatipinnis

  • Species: Polypterus delhezi

  • Species: Polypterus senegalus

  • Species: Polypterus delhezi

Living Fossils

09 March 2018


Aquarists with an interest in ancient life are well served by the hobby, with some very archaic types of fish are readily available and in some cases easy to keep. Bichirs are the best examples, coming in a range of sizes from small species barely 30 cm long to giants more than three times that size. So long as you pick the one that suits the space you have available, you can't really go wrong with these adaptable, basically easy-going African fish.

Lungfish and gar are two further types of primitive fish, but unlike bichirs, they're best left to the more experienced aquarists. It's not that they're delicate, they're not, but their large size and predatory habits make them difficult to house and feed. On the other hand, these fish are impressive and can make good, long-lived pets if you have the space for them.

Bichirs

Almost certainly the easiest and more widely traded species of bichir is Polypterus senegalus, sometimes called Cuvier's Bichir or the Senegal Bichir. With a maximum length of 30-35 cm, this species can be housed in aquaria upwards of 150 litres, but being reasonably tolerant of its own kind, groups may be maintained in larger systems if you allow 40-50 litres for each additional specimen. Like other bichirs, this species is not fussy about water chemistry, and may be kept in anything from 2-20 degrees dH, pH 6-8, though neutral, slightly soft to medium hardness water is probably ideal. Similarly water temperature isn't a major issue, Polypterus senegalus happily adapting to anything between 24-28 degrees C. Because bichirs are 'jumpy', the aquarium should always be covered with a secure hood.

Bichirs are among the most primitive bony fish, possessing numerous unusual skeletal traits as well as fully functional lungs. In terms of looks Polypterus senegalus has the standard bichir build, that of a robust eel covered with thick scales and sporting numerous small dorsal finlets all the way along its back. It has stout pectoral and pelvic fins that it uses partly for swimming and partly to amble across the substrate while foraging for worms and other small meaty prey. Aquarium specimens are adaptable feeders, favouring krill, bloodworms, earthworms and other foods of that sort, and some specimens will also take good quality carnivore pellets. They are of course predatory and will consume bite-size prey, but when kept with medium sized community fish they are completely peaceful. Congo tetras, kribensis and Synodontis are examples of tankmates that would work within an African theme.

Click here for more about Polypterus senegalus and to see which stores currently have it in stock.

Polypterus senegalus has been bred in captivity, though commercially hormones are used to trigger spawning more consistently. Periodically the albino form of the species is traded. Whereas the wild-type fish is grey, the albino form is white and has the pink eyes typical of albino animals. Basic care is similar to that of the normally coloured form, but like other albino fish this bichir may be a little more delicate and certainly more sensitive to bright light. The prospective owner should bear this in mind and plan the aquarium accordingly.

Click here for more about Polypterus senegalus 'albino' and to see which stores currently have it in stock.

Polypterus delhezi is similar in size from Polypterus senegalus but not as commonly traded. It is a very handsome fish, steel-grey with a pale belly and six or more black, sharply defined saddle-like bands running over its back and down its flanks. It is one of the bichirs with a slightly protuberant lower jaw, indicating that it hunts more for small fish than invertebrates, unlike Polypterus senegalus, which has the more snub-nosed appearance for those bichirs that would normally hunt things like worms and insect larvae. Needless to say care should be taken when choosing tankmates, but given its adult size is around 35 cm, Congo tetras, nurse tetras and so on would make fine tankmates.

Aquarium maintenance matches that of Polypterus senegalus as described above, and under aquarium conditions it will each much the same types of food, though small pieces of white fish fillet will certainly be appreciated.

Click here for more about Polypterus delhezi and to see which stores currently have it in stock.

Towards the upper end of the size range is the Ornate Bichir, Polypterus ornatipinnis, with adult lengths around 60 cm under aquarium conditions. Obviously these are big, powerful fish that will need a large aquarium to do well. The classic 6 x 2 x 2 ft tank with a capacity of 600-700 litres is precisely the sort of aquarium you'd need to keep Polypterus ornatipinnis, particularly if you intend to keep it in a mixed species set-up alongside large characins, L-number catfish, stingrays and so on.

This is certainly a species well worth keeping. Its body is marked with a complex black and white pattern that includes orangey markings on its fins as well. While juveniles have larger black and white blotches than the adults, these fish retain their beautiful colouration even as they mature, and their pectoral fins often acquire additional ring-like bands as they get bigger, adding to their charm. Although predatory and usually fairly expensive, this infrequently imported bichir does well in captivity and gets along well with dissimilar species. It is, however, quite aggressive towards its own kind and likely other bichirs too.

Click here for more about Polypterus ornatipinnis and to see which stores currently have it in stock.

The Ropefish, Erpetoichthys calabaricus, is a hobby staple, widely sold and inexpensive. Although closely related to the bichirs, it differs from them in being much more slender in shape, almost snake-like, and with very much smaller head in proportion to its body than a typical bichir. Their pectoral fins are much smaller too, and they lack pelvic fins completely. On the other hand, like bichirs they have a series of small dorsal finlets quite unlike the one or two dorsal fins of typical aquarium fish. Overall colouration is emerald green with an orangey underside. There pelvic fins are dark green to black in colour.

Ropefish are gregarious and do best in groups of three or more specimens. They are shy and naturally nocturnal, and unless they feel very settled they tend to hide away in favoured cave with just their heads poking out. Because of the small size of its head the Ropefish isn't much of a predator, consuming small invertebrates such as insect larvae in the wild. This makes them safe with all but the smallest community fish; pretty much anything larger than a danio should be fine.

The biggest challenge with Ropefish is keeping them in tank! They are amphibious to a degree in the wild, slithering through swamps and marshes as they hunt for prey during the night. It's essential to ensure the aquarium is escape-proof, especially the hood, otherwise they will eventually escape.

Click here for more about Erpetoichthys calabaricus and to see which stores currently have it in stock.

Gar

Gar are nowadays an exclusively North American group, but fossil gar can be found elsewhere, including Europe. They are definitely ancient-looking animals with heavily armoured bodies and long snouts bristling with sharp pointed teeth. Other primitive features include the ability to breathe air using their swim bladder and their asymmetrical (rather shark-like) tail fin. Scientists recognise seven species across two genera, Lepisosteus and Atractosteus, but aquarists may also come across hybrids and artificial forms (like golden gar) from time to time.

All gar are rather large, even the smallest ones getting to about 60-70 cm under aquarium conditions. Obviously they need very spacious living quarters, upwards of 750 litres, and realistically the more the better.

They're arguably fish for public aquaria rather than home aquarists, though one or two species have some value. Chief among them is the Spotted Gar, Lepisosteus oculatus. Wild specimens can exceed 120 cm in length, but aquarium specimens are normally no more than 60 cm long. Although they are not fussy about water depth, the width and length of the tank is critical because these armoured fish can't turn around as easily as fish covered with more normal scales. Certainly the tank should measure at least twice the length of the fish from front to back, and at least four times the length of the fish from end to end. In other words, an aquarium 120 cm wide and 240 cm long would be the smallest viable system for an adult specimen.

Gar are not fussy feeders. They're carnivores, and tend to favour fresh and frozen foods such as lancefish, prawns, squid and so on. But settled specimens will also take good quality carnivore pellets. As always with carnivores it's important to minimise the consumption of thiaminase (found in mussels, prawns and cyprinid fish especially) and the use of a vitamin supplement is useful. Obviously they will consume very small tankmates, but if housed with fish of similar size they are extremely peaceful and easy going, working nicely with large but peaceful cichlids, L-numbers, stingrays and so on. Water chemistry is not a major issue, but being large predators they do need robust filtration if water quality is to be maintained. Gar are jumpy fish that should not be kept in open-topped tanks.

Click here for more about Lepisosteus oculatus and to see which stores currently have it in stock.

Lungfish

Whereas bichirs and gars are primitive fish from the evolutionary line that eventually produced bony fish, lungfish are primitive fish from the lineage that ultimately gave rise to the amphibians, and through them, reptiles, birds and mammals. This makes them very interesting from a biological point of view, but they have never been especially popular among aquarists. One problem is their large size, the African Protopterus species reaching lengths of up to 2 m in some cases. Protopterus are also notoriously grumpy and aggressive animals, and given their size this makes them impossible to keep in mixed species set-ups.

The South American Lungfish Lepidosiren paradoxa is smaller, up to 120 cm in length when fully grown, though aquarium specimens are usually much smaller. They are also much less aggressive, so while predatory, might be kept with armoured catfish of similar size, including various L-numbers and Doradidae. They are not much to look at (basically brown eel-like fish but very robust in build) but very interesting in many ways. Obviously they breathe air using their lungs, but they are in fact so dependent on air breathing that the adult fish have gills that are all but useless. Their paired fins are essentially thread-like and useless for swimming, but males develop feathery extensions to their pelvic fins that allow them to release oxygen into the water around their nests, ensuring the eggs and fry are able to respire. Curiously, the youngsters have external gills, like those of tadpoles; these atrophy as the fish mature.

Lepidosiren paradoxa is not difficult to keep. Because it is inactive it doesn't need a huge amount of space, despite its size, and a fully-grown adult could be maintained in a well-filtered 450-litre aquarium without problems. Smaller specimens can be housed in smaller tanks, but the wise aquarist won't push this too far, especially in mixed species situations. Lepidosiren paradoxa are jumpy though and a secure hood is essential, but with enough space between the water and the lights for the fish to gulp air comfortably. Because they are big and clumsy, it's best to use some type of heater that goes outside the aquarium, though a plastic heater guard might be used to protect a traditional aquarium heater if needs be. Feeding is not a major problem as they'll take all sorts of meaty foods of appropriate size, from krill and bloodworms for youngsters up to lancefish and earthworms for adults. But overfeeding can be a problem, as with any big, inactive predator likely to receive much more food in captivity than in the wild!

Click here for more about Lepidosiren paradoxa and to see which stores currently have it in stock.