Order Osteoglossiformes
Family Osteoglossidae
Perhaps there are few aquarium fish surrounded by as many legends, stories, and rumors as the arowana. Hardly many aquarium fish cost thousands of dollars. In China, the arowana is called the Dragon Fish. The Asian arowana is listed in the CITES Convention as a heavily protected animal. Trade is permitted only for a limited number of captive-bred Asian arowanas with appropriate certification. The arowana belongs to so-called primitive fishes that have survived unchanged since the Jurassic period.
Keeping an arowana in an aquarium is quite simple. Specimens that have lived to 40 years or more have been recorded. A characteristic feature of the arowana is the barbels on its lower lip. With such a mouth, the fish’s diet is clearly defined. The mouth resembles a trapdoor — it opens, swallows a cricket or a fish, and snaps shut. As a primitive fish, the arowana lacks teeth like a piranha, so it swallows its prey whole.
Despite being distributed across three continents, all arowanas inhabit similar environments. Externally, all representatives of the bony-tongue fishes are similar. This family features an elongated snout, a somewhat elongated body covered with large, prominent scales with a well-defined pattern, and dorsal and anal fins with soft rays extending along the entire body to the tail. The head is covered with bony plates. Especially characteristic in the appearance of these fishes are the dorsal and anal fins placed far back toward the tail, and low-set pectoral fins. The swim bladder in arowanas is very large; its walls are honeycombed and permeated with a dense network of blood vessels, allowing it to function similarly to a lung by absorbing oxygen from the air.
The entire appearance of the arowana — a scoop-like upper mouth, a long straight back, a dorsal fin set far back — demonstrates that these fish inhabit the uppermost, surface layer of water. Usually, facing against the current, arowanas make zigzag movements from side to side. Meanwhile, two sensitive barbels located on the lower jaw detect vibrations of insects that have fallen into the water and passing small animals. Hunting occurs not only in the water. The arowana often seizes insects, birds, reptiles, and mammals flying over the water surface or sitting on branches hanging over the water.
In the wild, Asian Arowanas are now quite rare. They are found in the islands of Indonesia, Malaysia, Thailand, Cambodia, and possibly Vietnam. Control over the catch and movement of wild Arowanas is extremely strict, so ideally, only captive-bred Arowanas from farms in Singapore, Malaysia, or Indonesia go on sale. Every captive-born Arowana has a certificate of origin which, like a passport, reflects information about the given specimen — country of origin, place and date of birth, color morph, as well as an embedded microchip under the skin encoding the identification number of that specimen. Using the chip number at the farm where the Arowana was born, one can obtain all information about the fish, as well as information about parents, brothers, sisters, and other relatives, which is important for breeding work. In certain cases, the company can share data on which country and to whom the fish was shipped.
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Actually, the name arowana is the native name of the most common species, Osteoglossum bicirrhosum. Thanks to aquarists and importers, the name arowana came to be applied to all fish closely related to this species. At the same time, Asian species are often referred to as the Asian arowana. Currently, arowanas are represented by Osteoglossum bicirrhosum, Osteoglossum ferreirai in South America, and in the Indo-Australian region by Scleropages species: S. aureus, S. formosus, S. inscriptus, S. legendrei, S. macrocephalus, S. jardinii, and S. leichardti. Some sources separate these variations into distinct species, while others consider these breeds as a single species, Scleropages formosus. This family has an elongated snout, a body covered with large, heavy scales, and soft-rayed dorsal and anal fins running along the entire body to the tail. Osteoglossid fishes are too large for a home aquarium.
A representative of the family frequently found not only in public aquariums but also in hobbyist tanks is the silver arowana (Osteoglossum bicirrhosum), inhabiting the same waters as the arawana/arapaima. The black arowana (Osteoglossum ferreirai) boasts an exquisite coloration of black and yellow stripes along its entire body. However, unfortunately, this coloration fades with age. The silver arowana practically does not change its coloration throughout its life.
Silver arowana — their unusual shape and large size quickly made them popular for office aquariums as well. The Asian arowana is imported much less frequently. This species has several color variations: red, gold, green, and red-tailed. The Red Arowana is one of the most expensive fish in the world. Australian species are best kept singly in species aquariums.
They are carnivorous, often feeding from the water surface. Osteoglossum species have been observed jumping nearly 2 meters out of the water, frequently snatching insects, birds, reptiles, and mammals flying over the water surface or sitting on overhanging branches. It is believed that young Arowanas can be well-fed with free-swimming guppy, molly, and swordtail fry. These can include not only livebearers but also goldfish and others. Arowanas feed exclusively on animal matter. If you wish to treat the fish, you can feed them insects, frogs, small fish, and shrimp. Frogs are a favorite food of many Arowana species.
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It is also very important not to forget to cover the arowana aquarium with glass lids to prevent the fish from jumping out. Successful keeping of Arowanas requires large aquariums with ample swimming space. The fish grow very fast and, although they may not reach their maximum natural sizes, they easily reach 40-50 cm. A deep aquarium is unnecessary for arowanas; even in a 40 cm high tank, the fish rarely descend to the bottom, practically only when hunting for escaping prey. However, the length of the aquarium is paramount — in any case, it should be at least 170 centimeters.
Breeding this giant in aquariums is rare. The main reason, naturally, is that in captivity, due to cramping and improper feeding, arowanas do not mature. During spawning, the male incubates enormous reddish-orange eggs up to 16 mm in diameter in his mouth for 50-60 days. Arowana eggs are very large, teardrop-shaped, with a huge nutrient reserve. The eggs continue to function as a yolk sac even in fry that have reached 6-7 cm in size, giving early juvenile arowanas a completely unusual appearance. Fry leaving the parental mouth reach 8-10 cm in length, meaning they are larger than many adult aquarium fish.
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There are many color variations of arowanas. Furthermore, as objects of selective breeding, fish farms produce arowanas with previously unknown color morphs. Often, inexperienced buyers are sold one arowana species under the guise of another, and since keeping conditions differ slightly, one must know the main distinctions. Unfortunately, fry of Australian and Asian arowanas are difficult to distinguish — they are all gray with huge eyes. Unlike Asian and Australian arowanas, this species has longer fins, with the dorsal fin extending almost to the middle of the back. From a distance, it appears as though the dorsal and ventral fins are connected with the tail. The forehead is horizontal, without a slope, and the mouth is more vertical. The fish is more flexible in its movements. Also, if you are patient, you can count the number of scales along the body. In the Silver Arowana, they are smaller and more numerous — 32-35. In the Asian one — about 21-25.
An arowana can also be distinguished by its coloration. Australian arowanas have dark scales with a pinkish tint at the edge. Juveniles do not have this — they are all gray. The main distinction is the spots on the tail and fins. In the Australian arowana, these are small, round spots of blue or dark colors. And of course, the price of the fish serves as a distinction. You are unlikely to buy an Asian arowana fry at the price of an Australian one. Although reverse examples exist — there are many hybrids between the two species, and jardini is frequently sold under the name Golden Australian Arowana, after which the word “Australian” is dropped and the price increases. Asian arowanas must have a certificate of authenticity and an implanted microchip.
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For ornamental fish enthusiasts and breeders, one part of the arowana’s body is very important and often determines the quality of the fish, especially evident in the perfection of shape and color ranges. The primary (base) color is usually surrounded by other colors. The arowana’s scales are divided into 6 levels/lines, counting from the base to the upper part of the body. The first line is located on the belly, the line above it is called the second level line, and so on up to the sixth level, which is located at the very top (back). See illustration.
Scleropages jardinii. Green Pearl, Red Pearl, Saratoga
— Australian arowanas — resemble Asian arowanas, but they have smaller scales with red spots. Asian arowanas have 5 rows, while Australian ones have 7 rows. Color varies greatly from copper to gold. Sometimes you can even encounter red and golden pearl arowanas. In the pearl arowana, the fins are usually black with a slight golden sheen. Spotted arowanas resemble the pearl arowana in appearance. Their fins and tail are dark, and the scales are smaller and more rounded, resembling spots. Australian red arowanas are very rare; their scales and fins are crimson-brown with golden dots. Golden pearl arowanas have golden spots and a more yellowish color than the ordinary Australian arowana.
Osteoglossum bicirrhosum, Osteoglossum ferreirai, Silver, Black arowana.
Arapaima gigas, Arapaima, Heterotis niloticus, Nile arowana. 
