Pondering Your Pond Fish: Your Unusual Questions Answered!

You may have wondered if your pond fish sleep, or whether they have teeth. You might also contemplate why fish smell or how much koi cost. We consulted with koi veterinarian Doctor Eric Johnson, also known as Doc J, on these and other puzzling questions about koi and goldfish. You might be surprised to find what you learn!

Do koi have teeth?

Koi encounter a lot of crunchy stuff as they sift through the mud and gravel on the bottom of a pond. An examination of the contents of the stomachs of wild carp reveals a mixture of plant and animal material, particularly crushed crayfish, snails, and worms. For this, koi need teeth to break up the food. They do indeed have rather large teeth located at the back of the throat behind their gill arches.

The teeth are so far back that it would be difficult to reach, even if you stuck your finger in the mouth of a large koi. They don’t use their teeth aggressively or defensively, so you’re safe teaching them how to eat from your hand. Their teeth are used to smash the food items against a boney palate on the upper surface of the throat area.

The teeth of koi come in three pairs, and they constantly develop and shed the crowns. You might be surprised to find these white, calcium rich crowns in the skimmer of your pond! The koi teeth look much like the molars of mammals such as cows and people.


koi in pond


Do pond fish sleep?

Fish do sleep, but not in the same manner as humans. Fish don’t have eyelids, so can’t close their eyes. Instead, fish catch periods of rest by floating in one place or nestling into a cozy spot at the bottom of your pond.


How can I tell if my koi are stressed?

Koi show stress by blushing red in their fins and on their bodies. This is caused by a stressful environment, such as poor water quality. It’s their way of showing you that something is wrong.


Why do fish smell?

Fish smell strongly because of amino acids in their secretions and tissues, which is rich in sulfur and very unstable once the fish dies. The amino acids break down quickly into volatile amines like ethylamine, which conveys a strong odor. When you get fish slime on your hands, it begins to decay almost immediately. That’s when you smell ethylamine. Your nose is keen to pick up these unpleasant amines and it typically means that something is spoiled and unfit to eat.


How many times can pond fish reproduce?

Koi and goldfish can reproduce twice in one year. Normally, a koi or goldfish spawns once per year, but there are situations where koi or goldfish may spawn in the spring and then again in the fall if the temperature is unseasonably warm. Goldfish are more likely than koi to have two spawns per year.


How expensive are koi?

In rare instances, some koi have sold for over one million dollars! Many show koi are sold for five figures. A koi’s value is related to the rarity of its pattern, and this is determined by the intensity of its colors and the pattern in which those colors occur. The rarer the fish’s finery, the more the fish is worth. Ultimately, a koi is only worth what someone is willing to pay for it.


pond fish- your questions answered


Are fish diseases contagious to humans?

There are a few diseases of pond fish which can transmit to a human who has an open wound exposed to the water. Various bacteria from koi are also infectious to humans and can be contracted via open wounds. So, the moral of the story is to keep any open wounds clear of the pond water.


Is the correct term for a pregnant goldfish “twit”?

The answer is yes! Over the last 40 years, in Australia and sometimes England, one common reference word for a gravid female goldfish has been some variant of the term “twit” or “twerp.” The proper term for a pregnant female fish is “gravid” with “twit” being the slang version.


If you keep koi or goldfish in the dark, will they eventually turn white?

A lot of young goldfish that start out orange or red will naturally turn white, even if kept in full sun. An example of this is the red cap oranda, which almost always turns pure white. Some fish will lose all their red, simply due to significant stress.

Any fish kept away from full sunlight, will become pale in their color. “A red fish will usually turn orange or even a brassy yellow without sunlight,” Doc Johnson says. “Kept in the dark, the effect would be more significant. However, the fish would not turn white just because it was kept in the dark.”


Do goldfish really have a three-second memory?

Despite this popular belief, most studies have found the concept of fish having a three-second memory to be a myth. On the contrary, their memories can last as long as three months! Veterinarian Dr. Richmond Loh used levers to train goldfish how to get food, and they remembered these lessons for several months without reinforcement.

There is also a man who trains a goldfish to do various tricks. Although they are easy and quick to train, the fish do not remember their routine for very long. Because they can only be trained when hungry, most training sessions are about 15 minutes long, up to twice per day.

The talented goldfish wouldn’t remember the order of its routine from day to day, but when rewarded for certain behaviors, it could be trained to put on a 15-minute show with little more than finger cues and food as a reward.


Other beliefs about koi

There are a few other beliefs about koi that are not scientifically proven to be true but would appear to hold merit based on the frequency of occurrence. For example, the more a fish costs, the more likely it is to become sick and possibly die, no matter how well you care for it. Of course, this is probably just Murphy’s Law.

And then there’s the old tale that naming your fish will surely increase its odds of developing an illness or becoming prey to predators. It’s quite common to hear a pond owner warn against naming koi. They’ll be able to back up that claim with story after story. At the end of the day, pond fish are a joy to keep. And like anything else, the more you become familiar with fish care, the more you’ll succeed.