Yes, contrary to popular belief, koi do in fact have teeth – quite a lot of them, too! The thing is, we just never get a chance to see them as they’re located way down, past the gills at the back of the throat. These kinds of teeth are called “pharyngeal teeth,” and can be found in a variety of freshwater fish, including goldfish, loach, and ornamental koi carp.
Since goldfish are much smaller in comparison, you may be able to spot the teeth under the correct angle and lighting while feeding. In terms of koi, you’d be lucky to be able to even reach that far down as their sheer size means their teeth are very well hidden.
Even though the teeth aren’t located in the mouth, they’re still attached to a bony structure called the pharyngeal bone, located just behind the gill chambers. This may not be a jaw bone, but the food is still chewed by koi with the help of a bony section (“carp stone”) located at the top of the pharynx (throat) right above the teeth. The food is crushed and ground up with a familiar chewing motion which can sometimes even be heard if you listen carefully enough.
Here’s a video showing what they actually look like and their relative size (they’re pretty small!):-
Can Koi Bite if I Feed Them? Are My Fingers Safe?
Koi have very muscular mouths and will be able to give your fingers a noticeable “pull” if they manage to get ahold of any while feeding. However, since their actual teeth are located far back inside their throat, it would be quite difficult for you to actually get nipped in the process. Koi also make sure to “taste” any food they suck up before moving it into chewing reach, and we’re most certainly not on their favourite foods list for that to happen.
In younger or smaller koi, you could technically reach far enough to touch their teeth, but for adult fish, they’re usually located past fingers’ reach, so you’d never get within range. If your koi has flukes (a type of parasite) which attach to the gills and you’re checking them over, you may be able to catch sight of the teeth as you check over their gill chambers, but even this is unlikely to lead to any biting. Any injury you have from touching the teeth is more likely caused due to the stress you’re putting on the koi, causing them to wiggle and gulp to get free.
In other words, you’re very unlikely to ever get bitten by a koi you’re feeding – even if a jumbo-sized one! They may look big and scary, but the worst you’ll encounter from a hungry carp is a slight pull of the finger and less food in your hand.
While they won’t actively hunt for other fish, anything a hungry koi can suck up into its mouth may become fish food pretty quickly. Even though koi are very unlikely to eat smaller fish, such as goldfish, they’ll happily gobble up fry (baby fish), tadpoles, snails, and pretty much any insect they can find. Just because they won’t eat smaller fish, however, doesn’t mean you won’t have problems.
Some koi are more temperamental than others, with every fish often having very distinct personalities. There is also a “pecking order” established in herding fish, with larger, more aggressive koi often being the ones in charge. Problems can arise when you have a more aggressive koi trying to maintain its pecking order in the presence of smaller fish, as the larger koi may choose to nip at the fins and tail of the fish to assert dominance in the pond. Luckily, this is actually quite rare and most of the time even the largest of koi are very docile fish, so you shouldn’t have anything to worry about if you want to put them together. Fully matured goldfish are even less likely to have problems, but none will actually be eaten by koi.
I think I found a koi tooth – Is that bad?
If you look hard enough, especially while cleaning your filter box, you may notice small white objects that may actually turn out to be teeth from your koi. This is perfectly normal and nothing to be alarmed about. Koi, just like other species of fish, will shed a certain amount of teeth naturally throughout their life.
You’ve likely heard of sharks having multiple rows of teeth, and while koi don’t hold lots of sets, they still shed old teeth in the same manner to make way for new teeth. In fact, koi may shed upwards of 30+ sets of teeth in their lifetime, so it’s fairly common for you to start finding old teeth around the pond the longer you have your fish.
As stated, the filter box is the most common place to find them as they’re easily sucked through your pump into the mechanical filter media. You may also notice them inside your bottom sludge if you start raking it out during a clean of the pond. Unless you have a lot of koi, which would mean a lot of shed teeth (sharp objects), you don’t need to remove them as they pose no major problems. However, they can eventually lead to tears in the liner or damaged filter media, so keeping up with general pond cleaning and equipment maintenance is important so that doesn’t happen.