Sturgeon Parasites

Trichodina or commonly called Trich by koi keepers is another parasites that you can't see without a microscope. If infected your fish's immunity system will be run down and other complications such as ulcers, fin rot and other bacterial infections will take hold.  It is similar in habit to Costia and Chilodonella.  All three are microscopic and are basically treated with the same medications that kills (ichIchthyophthirius or white spot).  Trichodina is not as common as the others and is not quite as dangerous though it still sets the koi or goldfish up for other problems.

Flukes belong to the family of a monogenetic named trematoda. These parasites have sets of hooks at the end portion of their body and with the help of these they affix themselves to
 the selected hosts. There are two varieties of parasites found on the bodies of koi fish, skin flukes (image on the right )
and gill flukes (image on the left ). The monogenean trematodas are similar to worms and can be 2mm long. An overstocked pool with dirty water is a perfect breeding place for this kind of microscopic intruder.
Skin flukes (Gyrodactylus) measure up to 0.4mm, and gill flukes (Dactylogyrus) are up to 2mm in length. Both types of Flukes can be found in small numbers on healthy fish, living on mucus and skin debris, without apparently causing any harm.

The fish louse (Argulus) is another common parasite affecting fish. It belongs to the class Branchiurans, which are ectoparasites of fish (any external parasitic organism). they live mainly in freshwater habitats and have flattened bodies comprised of five limb-bearing segments; the head has well-developed carapace lobes.
This flattened body means that they have a low profile when attached to the host fish but the adult Argulus can be seen without magnification, measuring up to 10mm in diameter.