Gary Cryer of Grand Champion Koi in Chandler, Oklahoma, once said, “From the time koi are hatched to the time they pass away, there is always something trying to kill them.”
When I first started selling koi and goldfish, it seemed that nothing could kill these swimming jewels — except yours truly!
The first fish farmer I bought from bagged up a few hundred pounds of goldfish and koi for me and sent me on my way. I was excited to think I was going to make so much money off all these fish.
However, reality soon set in. I set up some 1,000-gallon tanks and put the fish in them. Two short days later, the water was so green that we could not see well enough to catch the fish. We proceeded with a complete water change for all the tanks using city water with chlorine. We had no idea where to find large amounts of chlorine remover to make the water safe. So, we emptied the shelves of water conditioner at our local box store and paid a pretty penny, as their chemicals were intended for smaller, 10-gallon tanks.
The next morning, we found that several fish had jumped out overnight and were glued to the floor, looking up at the sky and wishing they had not made that final jump. We also found a few floaters, having died from what we called UND disease (or “up-n-died” disease).
I was reminded of some advice I had received somewhere along the way. “Do you want to make a small fortune? Take a large fortune and invest in fish. Before you know it, it will turn into a small fortune.”
From the time I purchased these initial fish up to today, I have learned many lessons the hard and costly way.
Water quality controls whether the fish ultimately thrive or suffer. When the water quality is good, fish grow and thrive. But once the quality starts to decline, a fish’s immune system will slow down and eventually fail. That’s when parasites and bacteria proliferate and attack them.
There are several conditions we monitor closely upon receiving fish and while keeping fish. First, when the fish arrive, is the water temperature close to the water in the bag? We don’t like to transfer fish into our tanks if the water temperature is more than 10 degrees higher or lower. An acclimation time of 20 minutes up to one hour may be required by letting the bag float in the new water. Slowly balance the water temperatures as much as possible before letting the fish into the new body of water.
Perform weekly pH tests, even if the water looks clear and fine. Remember that while fish can tolerate a fairly wide range of pH, a sharp increase or decrease in pH will stress the fish. We try to keep the pH stable and between 7.0 and 8.3. Ammonia levels can range from zero to 5.0 and above. High ammonia levels may be characterized by fish being lethargic or not eating, streaks in their tails or a smell coming from the water.
Nitrite levels should be as close to zero as possible. High nitrite levels are toxic to fish. Water changes and adding bacteria or even a salt addition will lower a high nitrite level. Nitrates, by comparison, are not generally toxic to fish, but levels should still be close to zero. Reduce nitrates by adding plants, installing aeration or performing water changes.
Carbonate levels, or kH, may vary depending on your location. Here in Arkansas, we have very low amounts, so we constantly find ourselves adding sodium bicarbonate to stabilize or buffer the pH and keep the kH between 120 ppm and 200 ppm. This prevents wide swings from acid rain and natural oxygen swings over the course of a 24-hour day. Cold water can have oxygen levels as high as 10 ppm, while warm water without circulation may have levels as low as 3 to 4 ppm, which is certainly a stressor for fish. The cleaner the water, the fewer bacteria are needed, and generally the higher the oxygen levels are. We have made it a rule to keep every tank oxygenated with extra air stones moving the water aggressively from the bottom to the top of the pond to exchange gasses.
Parasites & Bacteria
There are a myriad of parasites easily visible to the naked eye and others that can only been seen with a microscope. The ability to identify what type of parasite is attacking a fish is paramount in determining the best treatment.
The main two visible parasites are fish lice and anchor worms. These two tend to attach all over a fish’s body. Because they have a chitin shell, the normal treatment are special insecticides such as Dimilin and Dylox, which are not readily available in all states. Physical removal is fairly easy to perform, but close inspection is required. Make sure they haven’t laid eggs that may hatch and continue to attach to fish.
There are other microscopic parasites in any body of water with fish; however, it’s important to determine whether the fish can naturally fend off these invaders, or if human treatment is necessary. We prophylactically treat for microscopic varieties coming out of winter and going into fall to keep the parasites at a low level. A microscope is highly recommended to view the tiny world that is not visible to the naked eye.
Also be wary of bacteria with scary names like aeromonas and pseudomonas. They generally are opportunistic, and a fish’s immune system may fend them off. Other virulent types like KHV (koi herpes virus) and SVC (spring viremia of carp) are widespread and can wipe out an entire population in a few days.
Effective quarantining and testing is the answer to keeping the bacteria in check. Infections can occur when parasites poke holes in the fish, or if a fish accidentally scrapes its body against a sharp edge or rock. Bacteria will capitalize and attack the fish from any newly opened puncture. To treat, coat fish food or distribute medicated fish food. Other methods include treating the entire body of water, or if the fish can be contained, you can give them shots. Special methods are needed to give shots, and this is generally not recommended for the novice, as more damage can be done to a fish if not done correctly.
The recommended number of fish per gallon ranges from 1 inch of fish per five gallons of water to 1 inch per 10 gallons of water. Can the concentration be higher? It depends on the water quality. If too many fish are in the pond and there are not enough good bacteria to take care of the waste, the ammonia will rise. pH may suffer. Oxygen levels will certainly decrease. Fish will not survive. However, if overcrowding occurs, nature will take care of it by removing fish, and generally the prettiest fish will be the first to perish.
Don’t overfeed, either. Simply put, koi should be fed what they can eat in five minutes. Feeding small amounts of food several times a day is preferable to feeding one or two large quantities. We have found that the best food is generally small, brown, round pellets whose first ingredient listed on the label is something akin to fish meal. High flour or wheat additives as the main ingredient is not as healthy as lower flour levels. Warmer weather will cause the fish to consume more, while cooler weather will have the fish eating less. Leaving food in the water will cause the water quality to decrease. The neighbor who has been tasked with feeding the fish may continue to throw in food, thinking the noise will cause the fish to eat. This well-meaning action will certainly cause issues with water quality, as the excess food will sour in the water.
When koi get in the mood to spawn, the female emits a pheromone that excites the male fish to tap or hit the female on her side. This causes the female to throw (or lay) eggs, and the male emits sperm to fertilize the eggs. During this time, the ammonia level will generally go up, and if the water is not buffered properly, the pH will go down. The action of the male hitting the female rubs the slime coat off both fish, exposing them to whatever parasites and bacteria are in the water. We have observed instances when a female would get hit by so many excited males that she would be exhausted to the point of hiding in rocks or a skimmer.
Gravid or egg-laden female fish that don’t lay eggs in a timely manner will soon become lethargic and can actually die if they do not shed the eggs. The proper conditions in the pond should get the female to shed the eggs. However, if they are not released, they can kill the fish.
We have frequently observed that fish will not eat when predators are around. Raccoons and birds of prey on the hunt may preclude the fish from coming to the surface to eat. When fish don’t eat, they will suffer from lack of nutrition, and their immune system can and will be diminished. Snakes are a common problem in the warmer seasons. Although there are many non-venomous varieties of snakes that will not harm humans, they will still try to feed on fish in a pond.
Koi may have to get used to pumps and skimmers, too. Using a pump with suction that is too strong for the fish to get away from the intake, or adding a skimmer that allows fish to get inside but not leave, will soon lead to its demise. I have seen may fish sucked into a solids-handling pump where the intake was not in a skimmer or placed simply on the bottom of the pond. Skimmers are notorious for capturing fish and not letting them swim away from the current caused by a strong pump.
Our basic proposition to every customer is, “Your job is not to take care of the fish. Take care of the water, and the fish will take care of themselves.” We then sell them a complete test kit and show them how to use each one, detailing what the water parameters should be. Basic testing on a weekly basis should take around 10 minutes. During this time, most water problems can be corrected, and the fish will not only survive, but thrive!