What sick fish in rivers and lakes
About the most common parasites living on the bodies of fish. The questions of their vital activity are covered, are parasites so dangerous for humans, and much more.
Parasitological analysis of fish
Systematic scientific research that allows us to create a more or less complete list of fish parasites has not been carried out here since the 60s of the last century !!! There are, of course, very good and interesting works on this subject, but they relate, as a rule, to one particular reservoir, or a specific species of fish, or a specific parasite (group of parasites). And so, to look and describe everything in a row, making a complete parasitological analysis of all types of fish, in all regions of the country (from the capital to the very outskirts), in various reservoirs, in all seasons of the year – this has not happened for a long time.
Although, of course, in order to study in detail the parasitofauna (totality of parasites) of all species of fish in all reservoirs of the country, the work of several large institutes would have been required over the course of several generations. But it’s better to give a small piece of live, real information than not at all.
So what parasites live on the bodies of fish that live in rivers and lakes.
We are talking here purely about natural rivers and lakes, and not about private pond farms, they have their own specifics. It seems that one should not breed a boring long lecture and go deep into biological features, development cycles, taxonomic affiliation, etc. each of them. However, it is impossible not to touch on this issue at all, since many of the parasites are “in sight”, and a lot of questions arise in this connection.
Here, for example, is ectoparasite infusoria (not to be confused with slipper infusoria, she is an independent young lady, she did not hunt for a period of time with parasitism). This is an imposing, thick ichthyophthyrius, nimble as a little devil, trichodina, “dying heart” chylodonella, “glass on a leg” – apiasoma. All these fish parasites are visible only under a microscope, with the exception of particularly large, well-fed ichthyophthruses, which can reach 2 mm in diameter; the fish struck by them looks like it was sprinkled with semolina. Ciliates are not dangerous for fish in natural reservoirs, but when they penetrate into pond farms, where fish live in more cramped conditions, they can create very big problems, up to mass death.
The same applies to all other ectoparasites – microorganisms that live “outside” on the surface of the body, gills and fins of fish. These are monogenetic flukes — microscopic helminths, dactylogiruses and gyrodactyluses, as well as the “not very microscopic” diaplozone, a completely paradoxical creature consisting of two fused individuals. It is called in Latin – Diplozoon paradoxum, and the second Russian name is a spike. The fact is that young individuals of this parasite grow together in pairs with abdominal suction cups so as not to search for a sexual partner; the female reproductive system fuses with the male, and cross-fertilization occurs. And no one is an outsider to this creature, which at the same time looks like a butterfly and a two-headed eagle in camouflage, is no longer needed.
An ectoparasite is also a scribble geometer – a striped leech, which is attached by a wide “muzzle” to the body and fins of fish, or, even worse, lives in the oral cavity. Once, from the mouth of a kilogram bream, we took a dozen and a half of these leeches, while on the surface of the body we did not find a single one.
You can also see nasty grayish-brown pins peeping out from under the fish (crustacean genera of Lernaea), flat oval translucent blotches (crustacean genera of the argumentus, or fish louse), and on the gills – light paired dashes (crustacean of the Ergazilius genus).
The causative agents of the “ink disease” (trematodes of the genus postodiplostomum) that are clearly visible on the surface of the body and fins cannot be fully attributed to ectoparasites, since they are buried inside the skin of the fish and under the skin, forming cystic tubercles of black color. Cysts burst over time, parasites die, and ugly, blurry spots remain on the surface of the fish’s body for a long time.
Larvae of trematodes of the genus diplostom parasitize in the lenses of fish eyes. They are visible only under a microscope if the lens is crushed to a completely flat state between the glasses. These are oval, slowly moving formations, the number of which in one eye can reach several tens. Tilodelphis live in the eyes – long, wildly wriggling worms. The former parasitize mainly in peaceful fish, the latter in predators.
And what kind of helminths were not found when opening the fish!
Under the scales of carp and common carp, long red female filometers live. Female filometers of another species live between the rays of the fins of the crucian carp, and a third type of filometers lives in the cavity of the body of the bream. After fertilization, males of all three species remain to survive their eyelids in the swimming bladders, and females move to their final destination.