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The swim bladder is a gas-filled buoyancy organ which is present in many, but not all, fish, providing them with buoyancy and avoiding the need to swim constantly to remain afloat in the water column.
Swim bladder problems are commonly encountered in some kinds of tropical aquarium fish (cichlids) as a result of internal injury caused by aggression. Certain fancy goldfish varieties, such as moors, veiltails and orandas, are particularly prone to this condition, and often have misshapen swimbladders.
Swim bladder is caused by various factors, including sudden changes in temperature, although other factors, such as microbial infection, may be involved in some instances.
Although an affected fish usually appears in reasonable condition, it experiences difficulty in maintaining its position in the water. It may show a list to one side, for example, or even float on its side or back at the water surface or remain sunk on the bottom of the pond. If the fish exhibits sporadic floating problems, such that it swims normally for some of the time, this may indicate air-gulping and not a swim bladder problem.
Signs to Watch for:
Abnormal swimming behavior, with loss of neutral buoyancy. The affected fish may have problems in keeping its position in the pond. The swim bladder may be damaged so that it is unable to deflate or inflate, causing the fish to either float to the surface or sink to the substrate, respectively. In some cases the fish may swim nose/tail down or swim/float/lie on its side or even upside down.
Systemic bacterial infection is a major causative factor. Certain species of Protozoa (coccidia) and Nematode worms (roundworms) may cause swim bladder problems in cold water fish. Swim bladder problems may also result from pressure on the swim bladder caused by, for example, tumors, constipation, or dropsy. Loss or absence of buoyancy is a common symptom in the later stages of many other diseases, and temporarily in cases of shock.
Treatment
Since the exact causes of this problem are poorly understood, recommending a reliable treatment is difficult.
Air gulping occurs when fish feed greedily at the surface and suck in air with the food. One solution is to briefly hold the food just beneath the water surface so they quickly sink when released and have to be eaten in mid-water.
If the buoyancy problem is not due to air-gulping, then it could be a more serious condition affecting the swim bladder. Try moving the fish to shallow water, say 5" (13cm) depth. In the case of goldfish and other cold water fish, slowly increasing the water temperature by about 9°F (5°C) sometimes brings about an improvement.
Dosing the tank with an antibacterial remedy and/or pond salt may be affective in some cases. A veterinarian may be willing to X-ray the affected fish in order to visualize any damage or derangement of the swim bladder chambers. If swim bladder over inflation is discovered, it may be possible for the vet to aspirate the excess gas, although this does not always bring about a permanent cure.
Despite attempts at treatment, many cases of swim bladder problems fail to improve. If the affected fish seem very distressed or is unwilling or unable to feed then it might be kinder to put it down.