【明報專訊】Villain actors

The red bellied piranha (紅腹食人鯧), so named because it has a distinctive red belly, are commonly found in the ponds and creeks of the Amazon in South America. The word "piranha" comes from the indigenous (土著的) Brazilian language, Tup�q, and literally means "tooth-fish". When they clamp their jaws shut, the top and bottom teeth interlock, turning the mouth into a trap. Sounds scary, right? But are they really the blood-thirsty monsters that devour (吞食) humans, as they are portrayed in movies?

Gifted hunters

At about 24cm long and weighing around 3.5kg, the red bellied piranha are not particularly large. They usually swim in schools of 20 to 100 individuals, which means that as a group they are a force to be reckoned with! Their diet consists of insects, fish, crustaceans (甲殼動物), snails, worms, dead animals, seeds and plants. They spend most of their time hunting for food during the day, and are especially active during dusk and dawn. The school will hide among vegetation and wait for their prey to appear. And then they will attack! With razor-sharp teeth and powerful muscles connected to their jaw, piranhas can easily snap off portions of fins, scales, or muscles, in a single bite!

The red bellied piranha are natural-born predators. In addition to their bite, they have a keen sense of smell to locate their prey. They can sense minute changes in water pressure and currents using their lateral line system (體側線), and can see well even in dark, murky waters.

Bust the myth!

Despite being a notorious type of fish, studies have shown that red bellied piranha stay in groups for their own protection, not to kill whatever stands in their way. Though they are predators of various types of animals, they are also the prey, in turn. They are the targets of birds, river dolphins (淡水豚), as well as caimans, which are relatives of crocodiles and alligators. They are also caught by humans! In fact, part of the piranha's diet is plant-based. They also help keep the Amazon waters clean of carcasses.

There are indeed stories of piranha "feeding frenzies". Unfortunately, some of these come from staged incidents in which groups of piranha were intentionally starved for days and then fed on a large carcass. Reports of piranha attacking humans are extremely rare.

As predator, scavenger (食腐動物) and prey, the red bellied piranha play an important part in the Amazonian ecosystem. We too can play a part in balancing and protecting our ecosystems! Since all waters are inter-connected, it makes sense for every one of us to keep our rivers, streams and lakes clean, no matter where we are in the world.

Text & photos: Ocean Park Hong Kong

■Glossary

reckon with (phr v) 對付

snap off (phr v) 清脆地折斷

murky (adj) 混濁的

carcass (n) 動物屍體/殘骸

[Smarties' Power English 第247期]