According to IFLScience.com, despite the brain and heart not functioning, cells in the fish's body still respond to stimuli – including sodium. Dead fish will continue to move around until they use up all their energy stores. It doesn't mean the fish is alive or in any pain.
Fish can drift considerable distances downstream after they have died in a river. This can make it difficult to identify dead fish, and the exact site and time of death from telemetry studies. Furthermore, dead fish can be moved within the river, or taken out of the river, by scavengers.
After a few days, the internal organs of the dead fish decompose and a gas is formed. This gas causes the fish to once again float.
Fish are able to move even when they have been beheaded or gutted due to their unique anatomy and physiology. Fish have a series of reflexes that are responsible for their movements, such as the spinal reflex and the stretch reflex.
The fish's brains are very much dead, but most of their tissue is very much alive. The muscles in the fish contain adenosine triphosphate, the main source of energy for muscle contractions. "Most of the tissue... is actually still alive," a chemistry professor at the University of Virginia explained to Discovery News.
Neurobiologists have long recognized that fish have nervous systems that comprehend and respond to pain. Fish, like “higher vertebrates,” have neurotransmitters such as endorphins that relieve suffering—the only reason for their nervous systems to produce these painkillers is to alleviate pain.
Fish often remain unusually still after a fellow dies in the same aquarium. Researchers say this behavior is probably due to stress hormones released into the water by the dying fish.
Try to scoop the fish into your aquarium net.
Look for signs of struggle as you place the net around the fish's body. If your fish is just sleeping, they'll wake up and try to wiggle their way out of the net. If they don't, they could be dead or very sick.
While most fish remain motionless when they're sleeping, certain species of sharks must keep moving, even while at rest, to ventilate their gills. On an even more interesting note, some species of marine Parrotfish and Wrasses surround themselves with a mucus cocoon when the sleep.
The wild wriggling and squirming fish do when they're hooked and pulled from the water during catch-and-release fishing isn't just an automatic response—it's a conscious reaction to the pain they feel when a hook pierces their lips, jaws, or body.
That said, the decomposition process can sometimes result in enough gas being produced and trapped inside the fish to cause it to float to the surface. So in short, fish float upside when they die because many of them are top heavy and posses an organ in their lower region that is filled with air.
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. Usually, enough gas builds up in body cavities to make the corpse float, like an inflated balloon.
Any dead fish should be removed, as its body will quickly rot in the warm, bacteria-laden water. A corpse will pollute water, risking the health of other fish in the tank. If it died from disease the last thing you want is other fish consuming its body parts, so remove immediately.
Dead animals can carry a host of bacteria and viruses that can be passed on to humans and pets. Tularemia is a disease that can be spread to humans via contact with a dead animal. It is a bacteria usually found in mammals, especially rodents and rabbits, and sometimes fish and birds.
Sadly, a dead fish cannot be revived. However, all is not lost if you have lifeless fillets aging somewhere in your freezer since last summer.
Run your aquarium as normal for two weeks without fish and you should be fine. doing a water test right after your fish have died will be useless. You will have an ammonia spike from the dead fish. The time to test your water would have been before they died.
Key Takeaways. Dead fish float in water because decomposition fills the fish's gut with buoyant gases. The reason fish typically go "belly up" is because the spine of the fish is more dense than its belly.
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.
If you see your fish lying on the substrate, gasping for breath, that could indicate the beginnings of nitrate poisoning, and you'll need to do an immediate water change.
It's pretty easy to tell when fish are sleeping: they lie motionless, often at the bottom or near the surface of the water. They are slow to respond to things going on around them, or may not respond at all (see some sleeping catfish here). If you watch their gills, you'll notice they're breathing very slowly.
Place the goldfish in a container filled with cool water from his tank. The cool water contains oxygen and will help to revive your fish. Some experts also suggest placing your goldfish right back into the water in his tank, even if he appears dried out.
The natural death of the fish in a fish tank is said to be the end of your problems. As per the aquarium Vaastu, the dying fishes take away the problem with them. However, you should immediately replace the fish as soon as possible.
If your fish is swimming frantically without going anywhere, crashing at the bottom of his tank, rubbing himself on gravel or rocks, or locking his fins at his side, he may be experiencing significant stress.