Matt Clarke gets the rare opportunity to see mouthbrooding arowana and has a close look at their eggs and fry, and finds out how the farms breed them.
Dragon fish, or arowana, are one of most popular large fish with fishkeepers in the Far East and are considered lucky, so they can fetch massive prices.
The most colourful and the most unusual varieties attract the highest prices, which can rise well into the tens of thousands for exceptionally colourful specimens.
Most people consider Asian arowana to be members of a single species, Scleropages formosus, but recent - and controversial - molecular and colour-based studies by some authors have split the genus up to include a number of distinct species. The Asian species include Scleropages aureus, S. formosus, S. legendrei and Scleropages macrocephalus.
The many varieties of arowana sold in the trade today are descended from wild fish collected from various parts of Asia. It's these varieties which some experts consider to be valid species in their own right.
Arowanas are paternal mouthbrooders and produce small broods of fry and take a long time to reach maturity, so they've been vulnerable to exploitation for both food and the aquarium industry.
As a result, Asian arowanas have been protected under CITES, the Convention on International Trade in Endangered Species.
MicrochippedThe fish are not banned, and it is perfectly legal to trade in them, but the fish do have to be bred and captivity and all fish need to be tagged with a special identification microchip so authorities can tell that the fish are not taken from the wild.
All of the arowana farms in Singapore are regulated by the Agri-Food and Veterinary Authority (AVA), which monitors the fish on behalf of CITES under its Dragon fish Management Scheme.
At a size of around 15cm/6" or so, officials from the AVA visit farms and insert microchip tags into the offspring and provide a special certificate for each fish so that the suppliers can legally trade in them.
Several of the arowana suppliers we spoke to said that it was possible to tag smaller fish, but only if the tag was inserted into the body cavity.
However, this carries a risk of damaging the internal organs, so farms prefer to wait until the fish are larger and the tag can be inserted into the shoulder area by injecting the tag under the scales.
As a result, even the smallest fish tend to be expensive as farms have to rear them to a much larger size than most other fish species.
Arowana farmingAdults are kept in large shoals in massive mud ponds. Periodically, the ponds and harvested by teams of farm workers who wade through the pond using a giant seine net and remove any male fish which are brooding clutches of eggs or fry.
As the fish are so valuable, they're handled really carefully. The male is placed in a large aquarium and his mouth is prised open so the fry drop out onto the aquarium floor. He's then returned to an earthen pond for fattening up.
Each clutch contains 10-20 eggs, which measure around 15mm in diameter. The males brooding the eggs and fry, are quite easy to spot, as their buccal cavities (the fleshy gap between the jaws) is quite distended.
After about a week, the eggs hatch and a tiny 1cm long fry appears on top of each egg, still attached to a gigantic 15mm yolk sac.
After another month or so, the fish have grown to a size of around 2-3cm and have started to consume some of the nutrients in the yolk sac.
A week or two later, the yolk sac gets much smaller and the fish start to resemble their parents and try to swim. After about two months they become free-swimming and are released by the male.
Since there is a risk of predation by the parents and other fish, farmers remove the offspring and rear the fry in tanks of their own.
It takes up to a year for the offspring to reach a saleable size.