I have an 11 year old common goldfish and he has recently been having some swimming issues-but only in deep water after a few hours. He is fine in shallow water and he can swim fine for about 8-9 hours in his tank but any longer that that and he ends up on his side or swimming in a spiral pattern. Once this happens he will recover in a few hours once he is put in the shallow water. He seems fine otherwise-eating etc. normally and all water parameters are normal for a freshwater tank. He has been to the vet and on x-ray there was some increased density in the bones of the respiratory tract and they suspect that a bacterial infection is the cause, but the vet was unsure of why this would cause swimming problems. He is currently on a course of antibiotics and anti-inflammatory medications from the vet to try and help him. I am just wondering if anyone has any experience with this sort of presentation?
I do not think the swimming problem is related to the increased bone density so you need to take a look at other possible causes, it sounds to me like this might have a neurological cause like nerve damage.
Swimming normally for several hours before the symptoms begin is a bit strange, had it been swimbladder problems it should have been a constant problem.
Increased bone density in the respiratory organs of goldfish can have several causes, one is low oxygen. Over time this is often a result of living in water that is too hot; if the temperature is above 25 °C water can hold little dissolved gases - this causes the gills to work harder to keep the oxygen level up and the heart has to work harder too.
If a fish has swimbladder problems it will change the buoyancy of the fish, it will float or sink; this causes the fish to have a jerky swim pattern where it struggles to maintain its possition in the water.
Swimbladder problems can be caused by a viral or bacterial infection in the lining of the swimbladder or the tube leading to the swimbladder, internal deformities in the swimbladder or the tube leading to it can be the reason for chronic swimbladder problems.
A fish tipping over or laying upside down is not the same as swimbladder problems. This is often caused by neurological problems, probable causes for this is infection of the nerves or the brain, another cause is poisoning by nitrite-nicotine-insecticides or air fresheners in the room if inside. Outside pesticides might be the cause, CO2 poisoning can be a cause for this too.
The most common cause for problems in a fishtank is overfeeding, or that the tank is not properly cycled before fish are introduced to the tank.