the piscicolidae are parasitic on the blood of fishes. some species are host specific while others can accept a larger range of hosts. some, such as the european "piscicola geometra", take a blood meal and then drop off the host and hide somewhere while they digest the blood; some, mostly in marine or estuarine habitats with soft substrates, attach themselves temporarily to a crustacean after leaving their fish host; others remain attached to a fish semi-permanently. leeches are hermaphrodites and mating may take place on or off the fish host, but in either case, the cocoon, usually containing a single egg, is deposited elsewhere, usually stuck to a stone or piece of vegetation, or even to the carapace of a crustacean. when the egg hatches, the juvenile leech has approximately one week to find a suitable fish host for itself.