Most fish breathe when water moves across their gills. But if the gills are damaged or water cannot move across them, the fish can suffocate. They don't technically drown, because they don't inhale the water, but they do die from a lack of oxygen.
Before we go, here's another myth to be busted: all fish other than sharks die if they stop swimming. In reality, breathing in nonshark fish species is just as varied as it is in shark species. Some fish sleep on the ocean floor just as some sharks do.
Most other marine animals don't need to swim in order to stay alive. Many fish don't need to swim in order to breathe – as long as there's enough oxygen in the water, they survive just fine. For example, stingrays can be seen lying flat amongst the ocean floor.
A fish's respiratory system allows it to spend its entire life in water. It does not require to come to the surface of water frequently to breathe air. It gets necessary oxygen required to live in, from water through tiny blood vessels spread over the surface area of its gill and not from air.
“Fish do feel pain. It's likely different from what humans feel, but it is still a kind of pain.” At the anatomical level, fish have neurons known as nociceptors, which detect potential harm, such as high temperatures, intense pressure, and caustic chemicals.
The differences in acidity and dissolved oxygen, not to mention all of the fat, proteins, carbohydrates, and other minerals in the milk that might clog the creature's gills, would quickly spell trouble. The animal would likely die within minutes, if not sooner.
A fish breathes by first opening its mouth to gulp water in and then opening its gill flaps to let water out. This ensures that there is a constant flow of fresh water through its gill chambers, which are the pockets that contain the gills.
While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.
They rely on something called “ram ventilation” to push water through their gills. These are the fish that need to swim to breathe, because the forward movement is what pushes water through their gills.
Most fish are slightly denser than water, so sink immediately after death. However, like a drowned human, they become more buoyant over time as bacterial decomposition produces gases inside the body.
One common cause is improper water temperature. If your fish's water is too hot or too cold, they will be very inactive. Check your heater and verify that your aquarium is at the right level. Other possible causes are overfeeding and improper water quality.
Some sharks such as the nurse shark have spiracles that force water across their gills allowing for stationary rest. Sharks do not sleep like humans do, but instead have active and restful periods.
If fish are experiencing acute stress (i.e., gasping up at the surface, lying on the bottom and not moving, or darting around the aquarium), you can be pretty sure that the water has been poisoned in some way. Maybe cleaning sprays got into the aquarium, or something released toxins into the water.
Staying near the water-surface or piping ('gasping' or mouthing for air) Increased respiratory rate or laboured breathing. Flashing (scraping/scratching themselves against objects) Clamped fins (fins held flat against the body).
According to Collins Concise Dictionary, drowning is “to die or kill by immersion in liquid” – so no, fish cannot drown. However, they can suffocate when fresh water does not contain enough dissolved oxygen – either as a result of eutrophication (an excess of nutrients) or drought.
The answer is still no; as they live in water they probably don't take it in as a conscious response to seek out and drink water. Thirst is usually defined as a need or desire to drink water. It is unlikely that fish are responding to such a driving force. What about salmon?
Yes, fish experience both physical and emotional pain. Scientists say that it's likely a different type than what humans experience, but it's pain nonetheless. Fish have nerve cell endings called nociceptors, which alert their bodies to potential harm such as high temperatures, intense pressure, and harmful chemicals.
Fish-keepers sometimes see their pets 'glass surfing' – swimming repeatedly up and down the glass of the tank. This could be the aquatic equivalent of the pacing of a captive tiger that's bored from a lack of stimulation. But the fish could also be stressed from an overcrowded or unfamiliar tank.
Fish out of water are unable to breathe, and they slowly suffocate and die. Just as drowning is painful for humans, this experience is most likely painful for fish. Compounds like cortisol—the hormone associated with stress—can significantly increase during periods when fish are out of water.
Signs of Low Oxygen
They will swim less vigorously and even eat less often. As oxygen levels drop further, the fish will begin to show labored breathing and more rapid gill movements as they desperately attempt to get enough oxygen from the water by passing more water over their gills.
An aquarium fish can stay up to two days without oxygen (in still water) but they still need some more amount of oxygen to breathe and do their essential daily work.
In general, grieving is unlikely in fish - unless you have individually bonded fish which might be possible in some species.
Most goldfish live a relaxed existence, spending lazy days rummaging through neon pink gravel, bumping into gaudy ornaments, and getting fat on flakes and pellets. But our fishy friends have a secret superpower: they can survive in oxygen-depleted water for long amounts of time by producing alcohol.
As soon as a fish dies, the other fish in the tank will begin feasting on their former friend. It's not personal; it's nature. Don't assume they murdered their former tank mate. They are just taking the opportunity to have a fresh meal.