Black spot disease (fish)

The life cycle of the parasite typically involves a fish-eating bird, a snail and a fish.

[4] The black spot larvae grow to sexual maturity in the infected bird's intestine.

When the eggs reach water, they hatch into free-swimming organisms which then penetrate snails for further development.

[5] The dormant encapsulated larvae associated with black spot disease do not appear to harm their fish hosts.

In very rare cases, a large number of cysts may form in the tissues above the eye, which can lead to blindness.