All fish are potential carriers of a large number of different parasites. Most aquarium fish carry some number of parasites. In small amounts, these parasites are usually not harmful. They only become a danger to the fish when they multiply due to special circumstances. Since parasites multiply very quickly under favorable conditions, they can quickly become ill and, in the worst case, kill numerous fish.
A basic distinction can be made between parasites that live outside the fish on the body surface, the gills or the fins (ectoparasites) and parasites that live in the fish, such as e.g. B. in the blood and in organs (endoparasites) live.
Photos: Martina Berghauser
Cichlid with a parasite on its mouth. The parasite was gone 30 minutes after the photo was taken. The mouth initially remained swollen. If anyone recognizes the parasite, please email the contact with the name.
External parasites (ectoparasites)
These parasites cause many of the plague diseases in aquariums. The great danger of these parasites lies in their extremely high reproduction rate. While a few of these parasites are harmless and can be found in almost all aquariums, they multiply very quickly under favorable circumstances. In nature, many of the new pathogens die before they have found a new host.
Individual fish can then be severely affected, but the disease spreads only slowly and does not endanger the entire stock. Due to the high stocking density compared to nature, the fish in the aquarium come into contact with each other and with the parasites much more frequently than in nature. The parasites are therefore able to survive en masse and infect new victims. Even healthy fish are then often not able to successfully fight the sudden and massive infestation with their body’s own defences.
Since external parasites often invade the external organs such as B. the skin, they often open up points of attack for secondary diseases such as fungal infestation, bacterial infestation, etc.
Internal parasites (endoparasites)
Compared to external parasites, internal parasites are less common in aquariums, but are particularly difficult to detect and positively identify. Many of these parasites require intermediate hosts such as B. snails and are therefore not always present in the aquarium. They are therefore usually introduced with new fish or the corresponding intermediate hosts. Often they can only be recognized indirectly. Sluggishness and lethargy can be indicators of internal parasites. Some worms partially hang out of the anus. Many of these parasites can only be recognized after dissection of dead fish and with a microscope.
Detect infestation with parasites
A common mistake in treating fish diseases is suspecting the wrong disease and treating it with inappropriate remedies as a result. If a cure doesn’t work, another cure is tried. Not only is money wasted, valuable time is also lost and often such an approach harms the diseased fish more than no treatment at all, since any treatment additionally stresses and weakens the fish.
Most fish parasites can only be recognized with certainty using a microscope. However, many aquarists either lack a microscope or lack the experience to be able to identify the parasites with certainty.
Beginners usually lack both microscope and experience. Long-time aquarists have often learned from experience to recognize the most common diseases based on their symptoms.
Larger parasites such as worms or ichthyo can be seen with the naked eye. Typical indirect indications of parasites are:
- unusually frequent and violent chafing of the fish on rough surfaces or edges
- skin opacities
- Red stain
- heavy breathing
- mucus secretions
- inertia
- reluctance to eat
However, these symptoms can also be caused by other diseases, so these symptoms can only give indications and an accurate diagnosis must be made before treatment.
The different forms of parasites
All unicellular organisms (unicellular organisms) with a cell nucleus that is separated from the cell plasma are called protists. Very small protists that can actively move with the help of one or more flagella are the flagellates.
Among the flagellates, a distinction is made between the intestinal flagellates and the skin flagellates.
Ciliates are relatively large single-celled organisms whose entire surface is densely covered with cilia.
Through a coordinated movement of the lashes, the ciliates actively move or gather food. The ciliates include B. the pathogen Ichtyophthirius multifiliis (white spot disease).
Sporozoa are unicellular parasites that rarely occur in the aquarium, but are then difficult to treat.
Worms infest the surface or internal organs of fish in many different ways.
» Show everything about fish diseases on Amazon*