Tapeworm in Koi are nearly always
bothriocephalus acheilognathi. They can be a problem mainly from planted semi
wildlife koi ponds or bought in fish from raising ponds or mud
Many tape worm species have other host cycles e.g. birds, pond
snails, etc. but are not always detachable.
The fish loses weight like
hexamita. Mostly only a single fish is infected, it's very rare to have more
than one at time, but I have seen four in one pond.
It can be treated.
Tub the fish, wait for faeces, check for spores. If none are found treat for
tape worm just in case. This sounds very haphazard, but to be sure, you would
have to open the fish up.
Most tapeworm is sadly only found upon
postmortems, where parasite treatments, used via a wrong diagnosis, have been
given with a view to fish's condition or supposed starvation, which in a koi is
nearly impossible when kept in a pond. I have seen the latter in a tank.
Symptoms can mimic hexamita, fish tuberculosis.
When a fish has
carried the worm over a long period, the fish will look in a poor state. Very
thin like a tadpole, all head, very thin body, with eyes sunk. It finds
swimming hard and will eat if it can get to food. These are symptoms of TB as
well, so it may not be a worm. But at this stage, recovery is only at 10%. The
fish has lost most of its digestive tract to anorexic intestine.
Thankfully, it's not a common problem.
One of the few times you will ever see a live worm. I have
coloured it in