Can sick koi be fed? Salt can ease the burden on their internal organs

Aquarium keepers, did you know that inkoikeeping, salt can ease the burden on a koi's internal organs?

Next, let's talk about the koi's second osmotic pressure regulation function. So-called "osmotic pressure" refers to the movement of water in and out caused by differences in salt concentration. Normally, when the salt concentration inside a living body differs from the salt concentration outside it, water flows from the side with lower concentration to the side with higher concentration; that is, if the salt concentration inside the body is high, water will seep in, and if the salt concentration inside the body is low, water will seep out from inside the body.

Koi are freshwater fish, so pond water constantly seeps into their bodies. At such times, the outside water seeps into the body together with odors, which is why it is often said that "freshwater fish have a muddier smell than saltwater fish." In this way, koi are constantly affected by osmotic pressure and pond water seeps into their bodies, and they must expel this water; this action is called the osmotic pressure regulation function.

Koi urinate in order to expel water, so their kidneys are highly developed. Furthermore, if a koi's health is poor, its urination function (osmotic pressure regulation function) is burdened, and at such times salt is used to help the urination function. Specifically, by bringing the salt concentration of the pond water close to the salt concentration inside the koi's body, pond water no longer seeps into the koi's body, so the koi does not need to urinate, which lightens the burden on the kidneys. That salt concentration is about 0.5% (5 grams of salt per 1 liter of water), which is the concentration commonly used.

It is said that sick carp naturally move to the waters at river mouths, possibly in order to regulate osmotic pressure.