Why do fish swim upside down?
Diseases in fish can make them to swim as if they are drunk. Some fish also do swimming in upright position usually due to these diseases. The most commonly occurring disease in the goldfish is disease affecting the swim bladder. Fish like goldfish such as orandas, ranchus, ryukins, fantails and moors are those which can succumb to this condition. The fish might recover from these diseases sometimes and sometimes they may not. The fish swim in water as they are not denser or less dense than water. The fish which are living will not have any buoyancy. They do not float or sink and will be with the same density as that of water. The density of water and its pressure alters as we go deeper into the waters. The fish possess an organ which helps them to swim and dive inside waters. The organ that helps them to do this is called as swim bladder. This organ will take off oxygen from the gills and store it to generate more buoyancy. This organ will automatically do this function and is not controlled by the fish.
But, when the fish dies, it is observed to be floating on water upside down. It appears as if it is swimming upside down. When the fish are dead, the oxygen will remain stored in swim bladder and as their body no longer is open to the environment, all the gases that are accumulated in the stomach due to decomposition will make the fish to float upside down in water.
If the fish are unable to exhibit balance and are not able to sustain their position in waters, then it is due to problem of swim bladder. This swim bladder disease might result in the fish not being able to stay upright or swim in a strange manner and swim in an awkward manner. The fish also will stay upside down in the tank bottom. The swim bladder that is present below the vertebral column and above the abdominal cavity of the fish will help in maintaining its buoyancy and position in water. The usual functioning of swim bladder like inflation and deflation can cause the fish to swim properly.