Eyesight is important for any predator, both for depth perception and to locate prey. For Piranha which are diurnal, but can live in murky water eyesight is more important than ever.
So, can Piranhas see in the dark? In short, yes Piranha can see in the dark. Piranha see dark water as red, that gives them a perception when the light falls. Piranha are diurnal so are mainly active during the day, but they are not blind during the night. Other senses like hearing and smell assist but their lateral line measures changes in water pressure around them so they can monitor currents, other fish around them, and make them aware of large predators in the water.
The Piranhas Eyes
Piranhas have large eyes compared to the rest of their body. This allows a lot of light in, perfect for a fish that may find itself in murky flooded forest plains. Being diurnal, they have eyes primarily for adapted for daylight.
However, some of their predators, like the caiman are active at night, so they need to be capable of quick evasion in the middle of the night.
Their eyes have a reflective layer, that aids light entering the eye. Piranha have colored vision, as they contain cones, and their vision is monocular. This means they have great vision near to them but have the ability to focus on distant objects. They have perceptive distance ability so can take an accurate bite if they need to.
Piranha Vision
The Piranha is actually perfectly placed to see in dark or black looking water. Murky water is actually perceived by Piranha as a dark red, because vegetation soaks up other spectrum colors. Far red light penetrates the murky water and allows the Piranha the ability to hunt prey if it needs to.
The Piranha has vision perfectly compatible with the fact that water absorbs light the further the depth of the river or lake.
Perception Helps
It’s not just their vision that helps them be aware of their surroundings. Piranhas have a lateral line used to give perception to the surroundings they are in.
It is a line that runs the length of their body from the head to the tail which houses neuromasts. It allows the Piranha to sense or ‘see’ what is around them, whether a fish or foliage. Aquarium Piranha are more likely to receive better lighting than they do in their natural habitat, a fact that can stress them if it isn’t low light or there is adequate cover from the bright lights.
Do Fish Move Around In The Dark
If you have Piranha in an aquarium, you might be concerned about what happens when you turn out the lights. You can’t see across the room, so what about your Piranha.
This has an inverse as well, as to whether Piranha freak out once lights are turned on from a dark room. Frankly, people use very different strategies to deal with this.
Some keep a low level light on in the room, or low tank lights, or even a combination to give the impression of a darkening day. And the inverse happens for the dawning of the day.
Another option is a timer, where the tank lights turn on at a repset time to give equivalent day and night hours.
Piranha, preferentially at night will enter a rest state, that some may call sleep. They appear inert and unresponsive and their brain activity lowers. The lateral line keeps the fish subconsciously aware of their surroundings.
Conclusion
So Piranha are not helpless during the night. Despite having large eyes, and a vision that has depth perception, they see ‘dark red’ in the murky water allowing them to visually keep aware of what is around them.
They are assisted by other senses, notably smell and hearing but the lateral line is a motion detector that allows them to perceive the world around them. They sense changes in water pressure that gives them a full picture of what is going on around them.
In dark water, where there is little light, they will not swim around bumping into fixed objects and other fish.
Still, it is recommended to give tank Piranha a day and night routine, as they would in the wild, and place tank lights on a timer.
