This is one of the problems of having a heated system. I fully understand that Koi are not cold water fish but are more temperate and do benefit from a “cool spell”.
The objective of most Koi keepers having purchased a beautiful specimen, the quest is to help the Koi to grow to its full potential by providing it with a high protein diet and an expansive pond. The pond may even benefit from an additional source of heating to provide the Koi with healthy growing conditions.
If all goes to plan, the Koi will increase in length and volume at similar rates and grow into fish displaying well-proportioned bodies.
However, Koi will occasionally adopt an abnormal growth pattern, where its volume continues to increase without the associated increase in length.
This fat fish has an ovarian tumour. It is easlity distinguished from a pregnamt female as the swelling is mainly near the rear end and usually on one flank more than the other.
Besides being unsightly, such Koi will often swim with apparent discomfort, wriggling with difficulty and adopting a strange pose in the water. These symptoms are quite common, especially in older fish.
A fish suffering from a tumour is not likely to become as obviously bloated as a dropsied Koi, and it is only likely to affect a localised area of the fish. A tumour is likely to manifest itself as a lump, and the swelling may appear to one side if the Koi is viewed directly from above. As with dropsy, there is little remedial action that can be-carried out. Only the ovarian tumours have a tendency to swell the belly of the Koi.
Mature female Koi will naturally fill-out from spring through to summer when, if stimuli for spawning occur, they will spawn naturally in the pond.
It is quite common for older female Koi to reach July or August without spawning. Koi will respond to number of environmental stimuli, like sudden changes in temperature and water quality, or suitable mature males. If climate changes are not common during the summer, or the Koi are in heated ponds, then Koi will not be given the means through which to spawn - heated systems have their drawbacks.
Fatty degeneration of the internal organs
To grow Koi as quickly as possible, you may have fed them excessive quantities of energy-rich food, which will result in fat being deposited around the gut and internal organs. If this is the cause of the bloating then the majority of Koi in a pond are likely
to exhibit obese symptoms.
The remedy is to put your Koi on a diet. Change their food to a low-energy autumn/winter variety.
The belly of a Koi may bulge due to a build up of tissue fluid around the abdomen area. This can be caused by an internal bacterial infection or the malfunctioning of the kidneys. Behaving like a fluid-filled balloon, the volume and pressure within the Koi can cause blood capillaries to become visible in the skin and the eyes to protrude. This condition can easily be misdiagnosed as Koi being spawn-bound, but if scales protrude from the sleek lines of the Koi's body then this is a positive identification of a Koi suffering from dropsy. This illness is often terminal and can pose risks for other Koi in the same pond. Therefore, the affected fish should be isolated and monitored. If the affected Koi’s health deteriorates further it should be put to sleep with an overdose of anesthetic.
Thanks to Ben Helm for letting us use some of his content
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