It happens that fish get sick too.
Fish disease is an emergency for an aquarium hobbyist. Even experienced aquarists who seemingly follow care requirements knowledgeably can face fish diseases. Fortunately, diseases rarely occur in well-maintained aquariums. If a disease is suddenly detected in your aquarium, the urgent and deliberate measures you take will usually help avoid the worst. Many diseases, especially in their early stages, are curable.
Ichthyopathology — the science of fish diseases — divides them into contagious infectious and invasive diseases, as well as non-contagious ones. The causative agents of infectious diseases are viruses, bacteria, and fungi. Invasive diseases arise as a result of invasion — an attack on the fish’s body by animal parasites such as pathogenic infusoria, coelenterates, and worms. Some small crustaceans can also parasitize the bodies of fish. The occurrence of non-contagious diseases in most cases is associated with a violation of optimal keeping conditions for fish in the aquarium or improper handling of them.
External diseases, which usually appear on the fins and skin, are detected in the early stages and can be treated in a timely manner. Internal diseases are not as easy to identify, but most of them cause unnatural fish behavior that immediately becomes noticeable upon careful observation. Examples include loss of appetite, unnatural swimming trajectory, apathy, color change, especially darkening. Thus, even with internal diseases, an attentive aquarist will quickly spot that something is wrong.
It is important to follow this sequence: Observation — Diagnosis — Treatment. With regular and careful observation of the aquarium, many diseases can be detected in the early stages. In this case, the infected fish is not yet weakened, and there is a high probability that healthy fish will not become infected. For successful treatment, it is necessary to make a correct diagnosis. The use of medications according to a specific diagnosis avoids unnecessary stress on fish and plants. The choice of treatment method also depends on the diagnosis. Most diseases have similar symptoms, so an accurate diagnosis can only be made in a specialized laboratory using modern diagnostic tools.
Habitats for each species have their own characteristics. In their natural habitat, fish are exposed to various natural factors to which they have adapted over a long period. It is impossible to recreate good keeping conditions for all fish in general aquariums, unless, of course, you keep a single species of fish and try to create optimal conditions for that species. Parasites live on all fish, and because we cannot create natural keeping conditions, we impair the fish’s immunity and thereby give an advantage to parasites that can kill a weakened fish.
As is known, it is easier to prevent a disease than to cure it. The most effective remedy against a potential outbreak of fish diseases in the aquarium is prevention. The key to good fish health is maintaining optimal conditions of feeding, maintenance, aquarium water, and many other factors affecting fish health. Optimal conditions help fish resist diseases and strengthen their immunity. We cannot control the balance between fish and parasites, and therefore we must follow hygiene rules and avoid stressing the fish. By maintaining optimal fish keeping conditions and showing attentive and careful attitude towards them, diseases can be avoided or at least localized in time. If the fish do get sick, it is necessary to correctly identify the type of disease and immediately begin treatment. Accurate diagnosis will make treatment more successful. The above applies to all animals and objects brought into the aquarium.
Below are the phenomena and factors that can affect the well-being of fish and possibly contribute to diseases.
• Hunger and emaciation. Both can easily lead to contagious integumentary damage; fish are secondarily affected by fungus.
• Bad and unsuitable food. Easily leads to stomach and intestinal diseases. If the food is too fatty, it can lead to intestinal obesity. If the food is too monotonous and poor in vitamins, it can cause general weakening and liver degeneration. A little fasting will not harm the fish. It is just like with people: it is better to be hungry and alert than full and sluggish.
• Too low temperature. Fish can catch a cold too. The consequence of hypothermia is usually swim bladder inflammation and, consequently, a decrease in the body’s resistance. Sudden and sharp temperature changes and arbitrary transfer of fish should be avoided.
• Lack of oxygen. Most often forces fish to breathe heavily and thereby weakens them.
• Too soft water or too low pH. Far from every fish tolerates an unusually low pH well. Fish (like other livebearers), if they live in the coastal zone, do not tolerate particularly soft water or too low pH. The latter causes “acid disease” in them.
• Wounds due to contact with equipment or biting neighbors. Lead to fungal or bacterial wound infections. The selection of fish in the aquarium must be well thought out in advance.
Fish diseases.
Like other living organisms, fish are also subject to attack by ubiquitous microorganisms. Therefore, it is necessary to become familiar, at least in general terms, with some fish diseases and their causes, as timely recognition of these diseases and their treatment will help avoid unnecessary losses. This is doubly important when a large number of fish are concentrated in a single tank. Environment-induced diseases are associated with violations of temperature regime, chemical water reaction, and oxygen regime in the water. Such disturbances of the optimal habitat can lead to disease or intoxication of the fish organism. Danger for most freshwater fish species arises when pH rises above 9.0 and drops below 5.5.
As a result of the decomposition of organic matter in water, ammonia and nitrates appear. They are toxic and capable of causing fish poisoning even in relatively clean aquariums with old water. Dirty filters pose a particular danger. Danger can also arise from improper use of medications or from toxic substances entering the water.
A decrease in oxygen content can occur due to the presence of an excessive number of fish in the aquarium, from the decomposition of organic matter (food residues, decaying plants). This can be a consequence of excessive growth of plants and algae, which absorb oxygen dissolved in the water at night, releasing carbon dioxide, as well as a consequence of an unexpected drop in atmospheric pressure. Fed fish require more oxygen than hungry ones.
The reverse, although rarer, but no less harmful phenomenon is water supersaturation with oxygen. It can occur under intense sunlight illumination of plants or during intensive aeration. Frequent water changes, mixing warm and cold water can lead to spontaneous release of oxygen and the appearance of tiny air bubbles (white mist), which is very dangerous for fish as gas enters their circulatory system. The first sign of danger is the formation of gas bubbles under the fish’s skin, especially noticeable on the fins. Mass mortality of fish results from cardiac embolism.
Affected fish sometimes lose the ability to maintain a normal swimming posture. Some may lie on their sides, turn upside down, or swim on the water surface. Loss of balance can have many causes. Severe disease or poisoning can sometimes be to blame. The gas filling of the swim bladder, which functions as a buoyancy device, can be disrupted, causing the fish to lose balance. In other cases, the swim bladder may overinflate, causing the fish to float helplessly on the water surface. Unfortunately, swim bladder problems are difficult to treat.
Diseases caused by improper nutrition may be a consequence of feeding monotonous or spoiled food. Digestive disorders manifest as inflammation of the stomach and intestines (mucous excrement, body cavity enlargement, scale protrusion, etc.). Monotonous food lacking certain vitamins leads to avitaminosis, which undermines the health of fish.
Viroses and bacterioses. The spread of such diseases can be avoided by maintaining hygiene, strict quarantine of new fish, and creating an optimal habitat. At the same time, timely removal of sick and dead fish is an important measure to prevent an epidemic. The most common issues are infectious dropsy, furunculosis, tuberculosis, and bacterial fin rot.
Fungal diseases are usually the result of tissue damage in weakened fish kept in unfavorable conditions. Carriers of such diseases are fungi of the genera Saprolegnia and Achlya. Fungi usually appear on affected body parts, mycelium develops, grows, and spreads to healthy parts. Failure to treat fungal diseases exhausts the organism, leading to complete exhaustion, poisons it with toxic substances, and the fish dies.
Invasions can be caused by single-celled parasites living on the body of fish. They are brought into the aquarium with natural food or infected fish. Typical signs of invasion appear massively among fish species prone to such diseases. A rash appears on the body surface and fins, noticeable under a certain lighting angle or when transilluminating the fins. With a high degree of fish infestation, the rash is noticeable on the dorsal area of the body and resembles velvet. Fish, especially young ones, look emaciated, their fins become ragged and clumped, and if left untreated, they die.
When fish are infected with Ichthyobodo necatrix, resulting in a thin, wavy blue-gray film and reddened skin hematomas on the fish’s body; or when infected with the infusorian Ichthyophthirius, when the entire body and fins are covered with white specks. The infusorian is very sensitive to malachite green, thanks to which fish diseases caused by this infusorian have now become a very rare phenomenon.
Another causative agent of invasions can be internal and external parasites from the worm group, for example, Gyrodactylus and Dactylogyrus — parasites living on the gills. Signs of the disease include ragged fins, unnatural fish movements, and behavior similar to oxygen deficiency. Parasitic leeches of the genera Piscicola and Hemiclepsis, which can be carriers of blood-sucking parasites and other infections, can be introduced into the aquarium with natural food.
Parasitic crustaceans, most often fish lice (genus Argulus), also attack fish, sucking out their body cavity fluid. They enter the aquarium in most cases along with zooplankton.
Main mistakes leading to fish disease.
— Keeping fish in unsanitary conditions.
— Tap water is not treated to remove chlorine.
— Proper acclimatization and quarantine of newly acquired fish are not performed before placing them in the general aquarium.
— Adding incompatible fish species to the aquarium.
— The aquarium is too small for the acquired fish.
— Overcrowding the aquarium with fish, keeping them in cramped conditions. Failure to consider that small fish purchased will reach significant sizes when adult.
— Feeding monotonous, vitamin-poor, and expired food. Slow and bottom-dwelling fish do not get enough food.
— Water changes are irregular and insignificant. Aquarium water parameters are not tested.
— Low dissolved oxygen content in the water.
— Incorrect chemical composition of water for the fish being kept. Prolonged exposure to excessively hard or soft water.
— High concentration of free CO2.
— Mixing cold-water and tropical fish in the same aquarium. Water temperature too low or too high.
— Untimely detection and improper treatment of sick fish.
