Marine Creature of the Month Feb'20

Marine Creature of the Month

Famous Fish

Piranha 3D (2010). Photo from Syfy

Red Bellied Piranha: Piranha

Ok, so not technically "marine" but these Amazonian toothy delights are iconic, don't you agree?

Kingdom: Animalia

Class: Actinopterygii

Conservation Status: Not Evaluated (NE)

WHAT ARE THEY?

To put it bluntly, they are a fish. A freshwater fish with a laterally compressed body. They grow up to 50cm (20in) in length, but the average is closer to 35cm (14in). As the name would suggest, the adults sport a lovely red tinged belly. As juveniles, they are grey with dark spots which develop into a more silvery colour as they mature. Like with a lot of fish, they show sexual dimorphism - the ladies have redder bellies than the men. Their fins are black or red to orange across both genders.

Of course, when we think of piranhas we think of lots of razor sharp teeth! (And that it's a difficult word to spell!) They do have a mouthful of teeth which they mostly use for scavenging whatever they can find - be it fish or plant. Thanks to B-movie creature features, they are famous for attacking prey as a hoard and stripping the flesh from their victim in seconds. This actually happens rarely! Yet another misunderstood fish with a bad rep thanks to the mass media.

WHERE DO THEY LIVE?

They are found in abundance in Southern American waters - most famously the Amazon River. They are native to South America. They are more commonly found in the basins of rivers but have been found in flooded areas of rainforests. They tend to prefer whitewater - waters with high levels of suspended sediments and a neutral pH - at temperatures of 15-35C (59-95F). They can spend time in cooler waters as low as 10C (50F) but it is only for a short spell. There have been records of them living in black- and freshwater which are slightly more acidic than whitewater.

Photo from Piranha Guide

WHAT IS THEIR LIFE CYCLE?

As already mentioned, piranha are scavenger hunters eating whatever they can get their teeth on. Having said that, they are aggressive fish and have been known to attack larger prey, such a capybaras, if their numbers are large enough. But they are more likely to eat weak or dying animals than they are to actively hunt down something big. They are actually omnivorous, meaning they eat plants and meat alike. The smaller piranha tend to eat earlier in the day while the bigger and more mature fish hunt later on. While scavengers, piranhas have been known to hunt down prey or lie in wait for the ambush. Opportunists, I think!

Their reproductive cycle is a little bit of a mystery, having only been truly observed in aquaria. It is believed they are able to reproduce before they are a year old. Fertilisation is done externally, with the females laying several thousand eggs onto plant matter and the males doing their business afterwards. The eggs will hatch after only two or three days! The juveniles stay in the plants until they are big enough to defend themselves. They go from hiding from predators to becoming the big bad in the watery shadows. Adult piranhas will guard their nest sites among the water grasses and it seems this enough to keep the fish which would munch on their eggs at bay.

Piranha travel in shoals, believed to be a defense method. The iconic image of piranhas hunting as a pack is seemingly a myth, as there is little evidence to support the cooperative hunting theory. It's more likely to keep them safe from larger predators such a dolphins, caimans, and aquatic birds. They communicate among the shoal, making sounds by rapidly contracting the sonic muscles associated with the swimbladder. It makes a low drumming sounds and is designed to show aggression towards other fish.

WHAT THREATENS THEM?

Piranha populations are largely unthreatened - woohoo! They are fished by humans and hunted by other species, but they are still found in abundance. They are a popular aquarium fish and sold at all sizes. The aquarium trade can be dangerous for fish species if demand is greatly increased - just look at clown fish - but something tells me that thanks to their vicious reputation it's unlikely there will be a rush for them any time soon.

Naturally, the continuing global threats to our climate and environment are a factor in their wellbeing. The Amazon rainforest is still being torn down at an alarming rate in the name of farming and produce. It's only a matter of time before this wanton destruction catches up to the river and starts affecting the ecosystem more that it probably already is. And I'm sure the river is also subject to plastic pollution and the other crappy affects we're responsible for.

Photo by Sylvain Cordier @ Nature Picture Library

FUN FACTS

• My dad brought a souvenir piranha back from Brazil (dead and glazed on a stick) for reasons.
• There are 30 species of piranha which are actually vegetarian! They have squared teeth.
• When the piranha reproduce depends on the water levels.
• In their ecosystem, piranhas serve a similar purpose as vultures do on land.
• While they will eat most anything, they will not eat rotten meat.
• Juveniles will nip each others fin which heal surprisingly quickly.
• Piranhas are actually quite shy.

Photo from Britannica

Were you surprised by the piranha's true nature? Which is your favourite creature feature? Any suggestions for my next Famous Fish? Lemme know below!

Listening to: Smith & Thell