Selecting Healthy Koi for Your Pond or Aquarium
Seeking a koi in top-notch health should be foremost in your mind, even ahead of color and pattern. This requirement becomes especially important if the fish must be shipped by air or ride in a vehicle for several hours to get it home. Such handling, even at its best, can quickly stress out a healthy koi for several days. If the fish is below par to begin with, the trip can be fatal. Of course, even generic koi should be free of malformations.
Examining koi in a group
Before you pick out a particular koi from a group in a quarantine tub or a dealer’s show tank, look at them as a whole. Consider the following characteristics about the group:
- Are they oriented vertically in the water? Fish that are ill may list (tilt) from front to back or side to side. Unless they’re feeding, the head shouldn’t be oriented toward the bottom of the tank.
- Do they seem to move easily through the water with no jerkiness? Skeletal malformations, swim bladder problems, and a host of other conditions can disrupt normal swimming patterns.
- Are the fish rubbing themselves on the bottom of the tank or against objects within the tank? If so, they may be trying to dislodge parasites.
- Are the koi swimming about in a frenzied fashion, or do they seem unusually listless? Both behaviors can indicate water quality problems or disease.
- Are the koi gasping or gulping air at the surface of the water? This behavior can indicate low oxygen levels (which eventually stress the fish) or water quality problems.
If the answers to the preceding questions raise any concerns, ask to see another batch. Better yet, resist your impulsive urge and find another source. However, if the koi pass the group test with flying colors, you’re ready to take a closer look.
Assessing a single koi
Select the fish that interests you the most and ask to have it placed in a bowl. Take a few minutes to study it close up. Before you fall in love with its color or its pattern, get steely-eyed about its health. Expensive or not, buying an unhealthy fish makes no sense.
As you give the koi a good inspection, ask yourself the following questions. If you answer “Yes” to any of them, move on to another fish, tank, or supplier.
- Does the fish have any rough spots? Do its scales seem to puff out away from the body? Koi whose scales stand out from their body like a bas-relief may be exhibiting pinecone scale, a symptom of an overall internal infection, or enteritis, which causes such pressure from within that the fish actually bloats, pushing the scales out. This symptom is a very bad sign.
- Is it missing part of a fin or part of its tail?
- Looking at the overall proportions of the fish, do you notice any stubby parts?
- Is its mouth asymmetrical or its snout sharply pointed?
- As the fish swims past you, is one side of the body wider or more curved than the other, rendering the fish asymmetrical in appearance? Does the tail curve up or wiggle to one side only?
- Are the eyes cloudy or protrude abnormally?
You can also ask the dealer to bag the fish. When it’s in the bag, you can examine the koi’s mouth, underside, and tail. Signs of infection, such as fuzzy, grayish, or white patches, may appear on the lower aspects of the koi and aren’t otherwise easy to see.
Fish that look healthy may still carry external parasite eggs that won’t hatch until conditions are right. Be aware that transferring the fish to a new pond may give these eggs the opening they need to proliferate, particularly if the fish has been in a cool pond and is moved to your warmer pond. This problem doesn’t mean you bought an unhealthy fish or that the vendor’s a crook. No treatment kills external parasite eggs.