HEALTH
I have a pond containing three generations of goldfish—about 15 fish altogether. One of them is getting rounder and rounder, and I think it’s been like this too long for it to be eggs. The bulges are on both sides of the fish. What’s causing this and is there anything I can do about it?
LEA JOSEPH
PETER REPLIES: Possible causes of bodily swelling in goldfish include the following:
Egg-binding: Known technically as dystocia, this generally arises when a mature female fish fails to spawn, perhaps due to the absence of mature males or lack of environmental spawning triggers, such as too cold a temperature at spawning time. The unshed eggs, if not reabsorbed, may accumulate within the body, causing swelling, and can prove fatal in some cases.
Abnormal accumulation of fluid within the fish’s body, or ‘dropsy’: This can be caused by damage or disease affecting one or more organs involved in the fish’s osmoregulatory system (the system which regulates the fish’s internal salt and water balance). A diseased kidney or gills can lead to fluid accumulation, as can organ failure due to old age. Affected fish may exhibit raised scales and/or pop-eye and may display other signs of ill-health such as reduced activity, or loss of appetite. Where a highly infectious bacterial or viral disease is the cause, several fish may exhibit bodily swellings and associated symptoms.
Internal tumour: Certain internal tumours can cause fluid accumulation. One or more internal organs may be affected, depending on the size and location of the tumour, and affected fish may exhibit various signs of ill-health. Such tumours generally prove fatal over time.
Polycystic kidney disease: Also termed kidney enlargement disease, this commonly affects goldfish. The kidney tissue develops cysts and may enlarge massively over time, causing displacement to internal organs, including the swimbladders. Affected fish may show an asymmetric bodily swelling. In goldfish, kidney enlargement has often been linked to an infection with an internal parasite, Hoferellus carassii, which unfortunately, is virtually impossible to treat successfully. There may be other causes of polycystic kidney disease, including a genetic predisposition.
In the case of your fish, my
