The underwater world is home to an incredible array of fish species, some stranger than others. Among the most bizarre is the extremely rare two-headed arowana. This phenomenon, known as bicephaly, has been observed in the Asian arowana species, scientifically known as Scleropages formosus.

While the exact causes of bicephaly are not fully understood, research suggests that genetics play a larger role than environmental factors.

Survival Challenges

Two-headed arowana face significant challenges in the wild. Their physical limitations hinder their ability to swim and feed effectively, making survival unlikely. However, in artificial environments, such as aquariums, these fish have been known to survive, particularly when reared from hand-stripped eggs.

One documented case involved a two-headed arowana that was approximately 15cm long. Although both heads were functional, it was unclear which mouth and set of gills were primarily responsible for feeding and respiration. The fish exhibited distress, breathing heavily and struggling to swim.

Despite the survival of such individuals in controlled environments, ethical concerns arise. The question of whether it is right to rear these fish, knowing the challenges they face, remains a topic of debate. The answer, in many cases, points towards a resounding “no”.

Arowana: The ‘Lucky Fish’

Arowanas, belonging to the Osteoglossinae subfamily, are freshwater bony fish often referred to as “bony tongues” or “lucky fish” in some Asian cultures. These ancient creatures have a long evolutionary history, dating back at least 150 million years.

These fish are popular among aquarists and can grow to impressive sizes, typically reaching lengths of two to three feet and weighing between six and ten pounds, with some individuals reaching up to 20 pounds. They are known for their distinctive lower jaw equipped with numerous teeth, including teeth on their tongues, which they use to tear apart their prey.

Arowanas are easily recognisable due to their:

  • bony, elongated bodies
  • large, heavy scales with a mosaic pattern
  • long pectoral, dorsal, and anal fins

These features contribute to their dragon-like appearance, further adding to their allure.

The Asian arowana, in particular, commands high prices in the aquarium trade, with individual fish often costing thousands of pounds. Other arowana species, such as the silver arowana (Osteoglossum bicirrhosum) and the black arowana (Osteoglossum ferreirai) from South America, are more affordable options.

A Spectrum of Colours

Arowanas exhibit a striking range of colours. The Asian arowana, for instance, can be found in hues ranging from stark white and pearly silver to gold, bright red, and green.

The existence of two-headed arowanas serves as a reminder of the incredible diversity and occasional oddities found within the fish world. While the survival of such individuals raises ethical questions, their presence sparks curiosity and encourages a deeper understanding of the complexities of the natural world.

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