【明報專訊】A fish out of water. Must be a difficult situation, isn't it? Not so for the fish named arapaima (海象魚). In fact, the arapaima is equally comfortable in water and out of water. Such is the wonder of nature!

1. Fish in dual action

Found in the web of rivers of the Amazon River Basin flood plains, the arapaima has well adapted to its low-oxygen habitat. Nature has given this special fish the ability to breathe air! The arapaima can breathe in two ways. It has small gills (鰓) for breathing in water, just like any other fish, and also a swim bladder (鰾) that works like a lung, which allows it to breathe air above water.

2. Amazing adaptation to nature

Necessity has made the arapaimas develop this awesome natural gift. The slow-flowing rivers they live in are low in oxygen during the dry season. For the other half of the year, when water is abundant (充足的) and the rivers overflow onto the flood plains, the arapaimas are carried to forests miles away. These forests are full of decaying vegetation and the floodwater has a very low oxygen content. Most fishes struggle to survive in such water, but not the arapaima. This amazing fish surfaces above water every 10 to 20 minutes to breathe air. It can survive as long as 24 hours out of water!

3. Iconic fish of the Amazon

Reaching three metres and weighing 200kg, it is possibly the largest freshwater fish in the world. The arapaima has a wide mouth and a bony tongue, which work well in combination with its sharp teeth.

When it opens its wide mouth, it creates a vacuum which pulls in nearby prey (獵物). The prey is quickly crushed by its tongue and teeth. The diet of the arapaima includes mostly fish, but it also feeds on fruit, seeds, insects and small animals found on the water surface.

But even the resilient arapaima is under threat. Because of its habit of breathing air with a loud gulp, they are easy targets for fishermen. Many arapaimas no longer live and grow as large as they might in a natural life cycle. Although it may seem that we are far from the Amazon, we can still help by protecting forest resources and consuming only the fish that are sustainable.

Text and photos: Ocean Park Hong Kong

■Glossary

survive (v) 生存

diet (n) 飲食

resilient (adj) 適應力強的

threat (adj) 威脅

[Smarties' Power English 第258期]