African Leopard Lungfish and Fish Guides for all Types of Unusual Fish
African Leopard Lungfish

What are unusual fish? These are simply strange fish…  rare fish, odd fish and downright weird fish!

Unusual fish are types of tropical fish that just don’t fit any of the typical groups. This a collection of the odd fish containing various true bony fish such as the Arapaima and Butterflyfish, pseudo-bony fish like the gar, pike, and sturgeonfish, as well as lungfish and a bunch of other strange fish. These specimens make fascinating aquarium inhabitants, and an impressive display of unique showpieces for top-notch aquarists.

There are many true bony fish and pseudo-bony fish families, and they are found in both freshwater and sea water. Odd fish included here are true bony fish families that often have very few species, sometimes containing only one. The pseudo-bony fish are most closely related to the true bony fishes, and are very similar, but they are much older in an evolutionary sense. Lungfish, also known as salamanderfish, are also some very primitive fish but there are very few species.

These fish are truly unique aquarium specimens. The unusual fish species list below includes familiar varieties and lesser known species of rather strange fish. Each fish guide has in-depth fish information including their places of origin, habitats and behaviors as well as the fish care needed for successfully keeping them in the aquarium. Fish pictures are also provided within each fish guide to help with fish identification and to aid in choosing pet fish.

Placed in their own sections are true bony fish and pseudo-bony fish families that contain a number of species. True bony fish types include cyprinids (barbs, danios), characins (tetras), catfish, eels, elephant snout fish, killifish, knifefish, loaches, hillstream loaches, and puffers. Pseudo-bony fish types include families like bichers and ropefish.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

Bony-Tongued Fish
Sub-order: Osteoglossoidei
Large freshwater species like Arapaima and Arowana to unusual fish like Butterflyfish

The bony-tongued fishes include a number of large and unusual freshwater species. There are seven families, six genera and 34 species.

The Arapaima is one of the largest of all freshwater fish. The Arowana, of which there are several kinds, is a fairly common aquarium fish that usually surprises the owner with its’ size and beauty. The Butterfyfish, though very similar to these others, does have some significant differences. The male anal fin has been transformed into the genital organ. Butterflyfish eggs are fertilized internally so the fry are born alive.

Click for more info on African Butterflyfish
Pantodon buchholzi
Click for more info on Arapaima
Arapaima gigas
Click for more info on Silver Arowana
Osteoglossum bicirrhosum

Order: Pleuronectiformes
Tonguefish, Sole, and Flounder, Soleidae “sandal” family of flat bottom dwelling fish

The flatfish or sole family, Soleidae, consists of 22 genera containing 89 species. Popular flatfish are Tonguefish, Sole, and Flounder. Flatfish are found in tropical areas of America, Africa, Asia, and Australia; primarily in the ocean but with some that are found in both brackish and freshwaters.

The name sole comes from the latin word ‘solea’ which means sandal. As both the name ‘sole’ and the name ‘flatfish’ suggest, these are flat, bottom dwelling fish. They have elongated bodies with both eyes on one side (the right side) and a single gill shaped like a slit at the base of the throat. They can breathe atmostpheric air both through this gill cavity and from parts of the hind gut, enabling some species to live at the waters edge.

Click for more info on Tonguefish
Brachirus panoides

Order: Lepidosireniformes
True to their name, Lungfish have lungs and need to breathe air!

Unusual fish known as Lungfish or Salamanderfish. members of the Sub-class Dipnoi, are unique in that they have characteristics of very primitive Osteichthyes (Super-class of bony fish). These intriguing fish are comprised of only 6 known species.

The African Lungfish (family Protopteridae)  contains 1 genera and 4 species and is found in western and central Africa. The South American Lungfish (family Lepidosirenidae) is found in the northern and central parts of South America. It has just 1 genera and 1 species and is also called the Aestivating lungfish. From south-eastern Queensland, Australia is the Queensland Lungfish (Family Ceratodontidae) which also has just 1 genera and 1 species.

Lungfish have an eel like body that is moderately elongated with small round scales, They also have air bladders or lungs. The Lepidosireniformes are able to aestivate during dry periods. Aestivation is a state of reduced metabolism which enables these fish to survive by burrowing into a mud hole and enclose themselves in a mucous cocoon. The eggs are laid in muddy holes and guarded by the male. The Ceratodontiformes from Queensland differs in that it can only survive a few days out of water, and then only if it is kept moist.

Click for more info on Marbled Lungfish
Protopterus aethiopicus aethiopicus
Click for more info on South American Lungfish
Lepidosiren paradoxa

Unusual Fish
Unique bony fish, weird pseudo-bony fish… and other odd fish!

Strange fish and each unique…  there are lots of very unusual fish!  The range of bony fish and pseudo-bony is vast. Some date back to an ancient prehistoric world,  others offer a unique and delicate beauty. Fish like the Gar and Sturgeon are some very, almost scary odd fish  and  other types are simply weird fish.

Click for more info on Freshwater Lionfish
Batrachomoeus trispinosus
Click for more info on Needle Nose Gar
Xenentodon cancila

True Bony Fish Types

There are many true bony fish and pseudo-bony fish families, and they are found in both freshwater and sea water. Their classification has been undergoing revisions in recent years. Currently, starting with the “Bony Fish” of the Super-class Osteichthyes , the true bony fish and pseudo-bony fish are placed within it as members of the Class Actinopterygii, or “Ray-Finned Fishes”. This class is divided into two Sub-classes, Chondrostei and Neopterygii. The Sub-class Neopterygii itself contains two Infraclasses, Holostei and Teleostei. The “true bony fish” are members of the Infraclass Teleostei.

Odd fish included here are some very interesting members of the Teleostei Infraclass. These range from one of the largest of all freshwater fish, the Arapaima, to the fancy Butterfyfish, the stick-like needlefish and flatfish like the Tonguefish.

Pseudo-bony Fish Types

The pseudo-bony fish include members of families such as true gars, pikes, and sturgeonfish. These are also members of the Super-class Osteichthyes of “Bony Fish” in the Class Actinopterygii of “Ray-Finned Fishes”. But at this juncture some are members of the Sub-class Chondrostei (sturgeon), while others are also in the Sub-class Neopterygii (flounder, gar, pike). These fish are most closely related to the true bony fishes, and are very similar, but they are much older in an evolutionary sense. Pseudo-bony fishes include such as families of true gar, pike, flounder, and sturgeonfish as well as families like bichers and ropefish.

Lungfish Types

Lungfish, also known as salamanderfish, have a different classification structure. They also start with the “Bony Fish” of the Super-class Osteichthyes at the top. But they then branch into the Class Sarcopterygii of “Lobe-finned Fish” and are placed in the Subclass Dipnoi which has two Orders, Ceratodontiformes and Lepidosireniformes. The lungfish also retain some of the very primitive characteristics of the Osteichthyes, but there are only about 3 species.

 Arapaima gigas at National Zoo (Image Credit: Jeff Kubina, Wikimedia Commons CC BY-SA 2.0 Generic)