Fish are often thought to be immune to drowning since they live and breathe underwater. However, the reality is more complex. While fish cannot technically drown in the same way humans do, they can still suffer from a lack of oxygen, leading to suffocation and ultimately death.
The Difference Between Drowning and Suffocating
Drowning, as defined by the Collins Concise Dictionary, is “to die or kill by immersion in liquid.” This term is not entirely accurate when applied to fish. Fish have gills, which allow them to extract oxygen from water, rather than lungs that take in air like humans.
When a fish is unable to obtain sufficient oxygen from the water, it experiences suffocation. This can happen due to various reasons, such as:
Damaged or blocked gills, often caused by fishing equipment or disease
Lack of water movement, which reduces oxygen levels
High water temperatures, which decrease the amount of dissolved oxygen
Excess plant and animal waste in the aquarium, depleting oxygen levels
How Fish Breathe Underwater
Fish have a unique respiratory system adapted to their aquatic environment. They use their mouths to take in water, which then passes over their gills. The gills are rich in blood vessels, allowing for efficient gas exchange. Oxygen from the water diffuses into the blood, while carbon dioxide is expelled.
Some fish, like sharks, must swim constantly to ensure water flows over their gills. Others, such as nurse sharks, rays, and skates, can pump water through their mouths and over their gills while at rest.
Exceptions: Fish That Can Breathe Air
While most fish rely on water to obtain oxygen, there are a few exceptions that can breathe air directly:
Lungfish
Lungfish, which first appeared around 400 million years ago, have primitive lungs adapted from their swim bladders. They come to the surface to breathe air and can survive periods of drought by burrowing into mud.
Arapaima
The arapaima, the largest freshwater fish in the world, can survive out of water for up to 24 hours. It has small gills and a modified swim bladder that allows it to take in oxygen from the air.
Marine Mammals and Reptiles
While not fish, marine mammals and reptiles like whales, dolphins, and turtles also need to surface to breathe air. They are adapted to holding their breath for much longer periods than humans, with the record held by a Cuvier’s beaked whale that dived for 138 minutes.
The Impact of Climate Change
As ocean temperatures rise due to climate change, the amount of dissolved oxygen in the water decreases. This can lead to the formation of “dead zones” with lower oxygen levels, putting fish populations at risk.
Some fish species are better equipped to tolerate higher temperatures than others. Those that live in variable environments, such as estuaries, typically have a greater tolerance to environmental changes compared to fish that live in the stable open ocean.
Preventing Fish Suffocation
To ensure the health and well-being of aquarium fish, it is crucial to maintain proper water conditions. This includes:
Providing adequate water movement and surface area for gas exchange
Keeping the tank clean and performing regular water changes to remove waste
Monitoring water temperature and ensuring it remains within the optimal range for the specific fish species
By understanding the unique respiratory needs of fish and taking steps to maintain a healthy aquatic environment, fish enthusiasts can help prevent suffocation and ensure their finned friends thrive in captivity.