Diagnosing Disease in Fish

 Kevin has a relatively large backyard pond.

┬áThe pond begins with a two-tiered waterfall and small stream section that terminates into the main pond area, which is 6 feet deep and contains about 12,000 gallons of water. Kevin’s pond also contains three turtles and 12 large koi carp, which have been in the pond since it was built some 10 years ago. The carp, however, are no longer the fingerlings they used to be.

The koi are now 14 to 20 inches long. Over the past three to four weeks, Kevin has noticed his fish acting more lethargic. Normally, when Kevin comes out to the pond in the morning, all 12 koi are waiting at the top of the water with gulping mouths. That has not been the case lately. Kevin now finds all 12 spending most of their time in one area of the pond near the bottom.

Kevin has netted a few of his fish to get a closer look and has noticed that their fins are showing bright red where they are normally a much more pale color. Other than this change, he notes nothing else physically abnormal. He has done his research on the Internet but has not reached any conclusions. That’s why he’s asking for help.

There are signs we can perceive from some species – dogs, cat, birds and rabbits – that we can understand, such as pain in a particular area or obvious signs like vomiting, diarrhea and coughing. With fish, that is not so much the case.

There is one clue we have with Kevin’s fish. Their fins are turning red. I would advise Kevin to pick out one fish from his group, preferably the one that appears to be most affected, and bring it to a veterinarian with experience working with fish.

The fin changes do likely hold an answer to why the fish are not thriving. I generally recommend a fin clipping in a case like this one. We take a few small pieces of affected fins and prepare them for microscopic examination. This will allow us to see what might be causing the changes in the fins.

There are several possibilities, including bacterial disease, fungal infection, protozoal infection and parasites. A fin clipping should be very helpful in ferreting out the answer.

A pond-water analysis also should be done. There may be something awry with water quality that has allowed a problem to occur with the fish. A veterinarian familiar with fish medicine will be able to help with pond analysis as well. If Kevin cannot find a veterinarian, he might be able to find help both for his fish and his pond through a retailer specializing in ponds and/or koi carp. The retailer will not likely be able to do fin analysis but probably will have significant experience with pond management and diseases in koi carp. The key, as always, is to get started. It is extremely unlikely that Kevin’s fish will get better on their own.

(Jeff Kahler is a veterinarian in Modesto, Calif. Questions can be submitted to Your Pet in care of LifeStyles, The Modesto Bee, P.O. Box 5256, Modesto CA 95352.)


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