First viewed by Practical Fishkeeping at Aquarama 2007 in Singapore, this poor Asian arowana, (Scleropages Formosus) hatched with two heads
The fish world is brimming with strange and unusual looking species. With over 34,000 different species found in the world’s waters, there are a few standouts which make our list of weird fish for a few different reasons. One that will certainly top the list and must surely go down in history as one of fishkeeping's most bizarre fish is the extremely rare two-headed arowana.
The two-headed arowana
This two-headed arowana is an extremely rare Asian arowana, Scleropages formosus, which has hatched with two heads (also known as bicephaly).
The causes of a fish or animal growing two heads aren't entirely known for sure, but research on this topic suggests that the result is likely due to genetics, rather than environmental factors (like our friend Blinky the three-eyed fish from The Simpsons.)
Can a two-headed arowana survive?
If a two-headed arowana is hatched in the wild, fry are unlikely to survive as they will have significant physical challenges which will reduce their ability to feed or swim, and therefore limit the chances of long-term survival.
Two-headed arowana fry are a more common occurrence when the fish are artificially reared from eggs that have been hand stripped, which means that the normally ill-fated fish can and do survive. The individual(s) pictured were approximately 15cm/6" long and on show in a bare tank at an exhibition.
While this arowana had two separate functioning heads, it was unclear as to which mouth and set of gills were doing the work.
The fish couldn't swim, lying on the bottom and flailing instead, with both fish heads breathing heavily and looking stressed. Whether the fish survived long term is unclear, however given the question of whether it should have been reared in the first place, the answer surely has to be a hard “no”.
What is an arowana?
Arowanas are freshwater bony fish belonging to the Osteoglossinae subfamily, also referred to as bony tongues, or ‘lucky fish’ within some Asian cultures. Arowanas are one of the larger fish species that is commonly kept by aquarists and usually grow to be two and three feet long. Most arowanas weigh between 6 and 10 pounds, but have been known to grow up to around 20 pounds.
They have a large lower jaw sporting many teeth for ripping apart their prey, including teeth on their tongues.
Arowanas are often called ‘fossil fish’ because of their long evolutionary history, and these ancient creatures have been around for at least 150 million years.
In the hobby, Asian arowana, Scleropages formosus, tend to command the highest prices, with individual fish frequently running in to thousands of pounds each. Silver arowana, Osteoglossum bicirrhosum, and black arowana, Osteoglossum ferreirai, both originate from South America and are considerably cheaper.
Arowana appearance
Unmistakably recognisable for their bony and elongated bodies, arowana are long and covered by large, heavy scales with a mosaic pattern on their sides. They have long pectoral, dorsal, and anal fins giving them their famous dragon-like appearance.
Despite their distinctive shape and appearance, arowanas (Asian arowana in particular) vary in colour and range from stark white, pearly silver to gold, bright red, and green.