This is an extremely variable species that, along with other members of the family, is becoming increasingly popular. Stingrays are most definitely not suitable for new aquarists and should in any case be treated with caution because of the dangers posed by the sting. Seek specialist advice and consult specialist literature before purchase.
Most sturgeons can grow to very large sizes—e.g. Huso huso (Beluga) can reach around 26ft (8m)—and are therefore totally unsuitable for aquaria. However, the Shovelnosed Sturgeon, along with Acipenser ruthenus (Sterlet) and A. stellatus (Stellate Sturgeon), are smaller and can be housed in aquaria as long as they are spacious enough. One of the reasons for their growth in popularity in certain countries — beginning in the late 1980s/early 1990s—has been the expansion of the pondkeeping/watergardening hobby in general, and that of Koi keeping in particular. Shovelnoses, Sterlets, and Stellate Sturgeons are transferred to outside ponds once they outgrow their aquaria.
This is the most widely available member of its genus. Although they have a number of characteristics in common with Erpetoichthys calabaricus (Ropefish), birchirs do not possess a snakelike body and do not lack a pelvic fin. Several other species are occasionally available: P. congicus (Congo Birchir), mainly from D. R. Congo; P. delhezi (Armored Birchir), also from D. R. Congo; P. palmas (Marbled Birchir) from Guinea, Liberia, Sierra Leone, and D. R. Congo; and P. senegalus (Cuvier’s or Senegal Birchir) from Senegal, Gambia, the Niger, White Nile, and several major lakes, such as Lakes Albert, Chad, and Rudolf. All of these species have similar requirements.
Ropefish is closely related to the birchirs (Polypterus spp.), with which it shares several characteristics, such as the possession of a number of dorsal finlets (7-13) rather than a single fin, and the ability to use its swimbladder as an auxiliary respiratory organ. It is distinguished from its relatives by its extremely elongated snakelike body and the lack of pelvic fins. Ropefish can survive out of water for several hours, as long as the air is humid.
This tough large fish is, like all other lungfishes, able to tolerate a wide range of conditions. As their native pools dry up in the wild, all the African species bury into the substratum and secrete a mucous cocoon within which they estivate (undergo a period of summer dormancy) until the rains return. The pectoral and pelvic fins of African Lungfish are long and whiplike rather than finlike.
This is the best known and most colorful of all the spiny eels. It is also among the largest and perhaps the most sensitive to poor water conditions as well as parasitic infections and injuries. Special care must therefore be taken to ensure that its aquarium requirements are scrupulously met.
Like all spiny eels, the Lesser Spiny Eel is an expert escape artist, so care should be taken to ensure the aquarium is well covered. The species is characterized by a number of prominent eyespots along the base of the dorsal fin and a series of darker and lighter bands running from snout to caudal peduncle. As in all spiny eels, the dorsal fin is preceded by numerous isolated small spines that can be raised, hence the common name for these interesting fish.
This legendary fish of the Far East is steeped in history and mystery and is one of the “greats” of the aquarium. In their native lands, Red Arowanas are said to bring health, wealth, and luck to their owners. As a result, they are highly sought after. The only specimens that can be legally traded are those bred in captivity and approved by the Convention in International Trade in Endangered Species (CITES). However, this species is now bred in such large numbers in captivity that current demand can be satisfactorily met. There are three main color varieties: silver/green, gold, and—the most highly prized and expensive—red. Several other varieties have been added and more are likely to follow. An Australian species, S. jardinii (Gulf Saratoga), is also now being bred in captivity, while another Australian species, S. leichardti (Spotted Saratoga), is only rarely seen.
Two species of Amazonian arowana are available, the Silver Arowana and O. ferreirai (Black Arowana) from the Rio Negro. The adults are very similar, although Silver Arowana is somewhat sturdier looking, with fewer lateral line scales, dorsal and anal fin rays, and vertebrae. Juvenile O. ferreirai exhibit the characteristic black coloration responsible for the common name of the species. Both these arowanas are excellent jumpers that can pluck prey from branches above the water surface. This ability has earned them the local name of macaco d’agua (water monkey).
This is one of the so-called glass knifefishes grouped by some authors, along with other related species, within the family Rhamphichthyidae. However, according to the classification followed here (as in Nelson 1994), the Rhamphichthyidae are known as the sand knifefishes and contain only two genera. Green Knifefish look particularly impressive in a shoal, where the establishment of a strict pecking order prevents fighting and, thus, injuries. Steatogenys duidae (elegans) (Barred Knifefish), Sternopygus macrurus (Variable Ghost Knifefish), and various species of Gymnotus, especially G. carapo (Banded Knifefish), all of which have similar requirements, are occasionally available.