Q. We have just installed a small outdoor pond — approximately 400 gallons (1500 liters) in volume and about 14 inches (36 centimeters) deep. We keep three very lovely koi in it. We plan to take our fish in for the winter because the pond will certainly freeze solid over the winter. Our question has to do with netting and moving the fish. What is the safest way to do this? I have heard that the moving process can be especially harmful to the fish.
A. Netting and moving koi and large goldfish can be very harmful to the animals if done carelessly or incorrectly. Many pond fish become very large in size and weight. Their bodies are meant to be suspended in water. If they are lifted up in a net and bounced around, severe physical injury could result.
Especially damaging with rough handling is the removal of the protective outer slime coat, which acts as an outer skin. Anytime the fish brushes against something slime is removed. In the process of netting the fish, this effect can be so extensive that the fish become vulnerable to infection and parasites.
Netting and moving can also produce internal physiological responses that weaken the animal’s immune system. This “stress” response can produce serious health problems days and weeks later. So, you are quite right to be concerned about proper procedure.
First, I strongly recommend that you use only shallow nets. There are a number of these that are marketed specifically for koi. The deep pocket nets sold in bait and tackle shops can seriously injure your fish. Given the price of good-quality koi these days, the price of a net is cheap — about $100.
Second, moving koi and goldfish with a net should be thought of more as corralling or herding. Slide the net below the fish, holding it parallel to the water surface. Keeping the net rim just above the fish’s eye level, guide the fish through the water. Again, do not try to lift the fish. Do not be surprised if the fish jumps the net rim.
Third, actual moving of the fish is done with a pail, pan or bucket. I prefer the large Rubbermaid-brand rectangular pails for this chore. The sides are high and the fish cannot leap out. Plus these pails have strong handles and the lids snap into place. These pails are available at most discount stores.
Partially submerge the pail in the pond and herd the fish into the pail. Once the fish is in the pail turn it right-side up. Pour out just enough water so that the fish’s dorsal fin remains submerged. Carry the animal to its destination, submerge the pail and tilt it so that the fish can swim out.
Studies have shown that you can decrease transport-induced health problems if you add salt to the destination pond or tank. The concentration should be about 1 gram of salt per liter of water. This is roughly equivalent to 1 pound (0.45 kilogram) of salt per 100 gallons (379 liters) of water. Maintain this level of salt for a week or so, and then you can begin to dilute it with water changes.
A second way to reduce stress is to use water from the original pond in the destination pond. That is, whenever possible, the destination pond should contain water removed from the origination pond. This way the fish do not need to adapt to new water chemistry. Then, over a period of days, partial water changes can be used to freshen the destination pond water.