Aquarium tropical fish and fish diseases


Osmoregulatory stress

Osmoregulatory stress

Latin name:
Other names: Osmoregulatory shock

Symptoms: Clamped fins, Disequilibrium (dizzyness), Excited behaviour, Fish are inert, Rapid breathing, Brightening (lighting) of body colors, Darkening of body color (Black discoloration), Fraying of fins

Fish may show common stress symptoms: abnormal light or dark coloration, abnormal behavior (lethargy or hyperactivity), clamped fins, rapid breathing. In advanced cases they will lose equilibrium.

Osmotic shock can be a result of a breakdown in osmoregulation due to inappropriate chemical composition of the water. It can also be caused by increased permeability of the skin resulting from a disease or trauma. Osmoregulation enables fish to maintain the proper balance of salt and water in the body, which is necessary to create optimal conditions for various physiological and biochemical processes. In all fish species osmoregulation developed in a way that enabled them to maintain the proper balance of salt and water in the water with chemical composition found in their natural habitat. If osmoregulation is disturbed due to adverse conditions (osmotic stress) or a sudden change in the chemical composition of water (osmotic shock), fish might not be able to physiologically cope wih it.
Chronic osmotic stress can eventually result in fishs death and osmotic shock can cause death very quickly.

Osmotic stress
It occurs when fish are kept in water with inadequate mineral levels (too high or too low). Osmotic stress affects more seriously fish whose natural habitat is rich in minerals and who are kept in th aquarium with a low mineral level, as osmotic gradients (difference) between the internal fluids of the fish and its surrounding environment (water) increase. Such fish have a less effective osmoregulation than those who are physiologically adapted to water with a low mineral level. That is why they are not able to cope with overloading of osmoregulation.
However, osmotic stress can occur if fish from ponds with a low mineral level are kept in hard water.

Osmotic shock
A sudden change in salt concentration (for example, if fish are transferred without gradual acclimatization from the water with a different mineral level). This causes death within 2-3 days and is a common reason for high mortality rates among newly introduced fish. High-concentration salt baths (used to treat, for example, external parasites) can also cause osmotic shock. All fish that show adverse reactions to such baths should be immediately returned into fresh water.
In less dangerous cases, when the difference in water conductivity is small, mucous membranes will flake away, which causes secondary infections. When the difference in is big, cartilaginous parts of fins can snap under high osmotic pressure. Large pieces of fins begin to fall off and the resulting wounds can be infected with fungi and bacteria, which happens because fish are weakened. Ammonia can also have an adverse effect on osmoregulation.

How to cure:
The concentration of mineral salts should be altered to suit a particular species. If osmotic shock occurs, this concordance should be exact and it should be established immediately. Newly-purchased fish if they are obviously affected should be transferred to the aquarium with appropriate chemical composition of water (for example, into a quarantine tank, where they should be kept for some time). Changing chemical composition of water in the main aquarium can cause osmotic shock in fish already living there.
Then change water in the quarantine tank so that its characteristics coincide with those in the main tank. This is done gradually, within 2-3 weeks. Only transfer can newly-acquired fish be transferred into the main aquarium.
If fish suffer from osmotic stress the concentration of dissolved salts should be changed gradually, within 1-2 weeks, so as to avoid osmotic shock.

Sera mineral salt

Osmotic shock can be avoided by gradually (sometimes within several days) balancing osmotic gradients between the fishs present and new habitat by means of water change. Under no circumstances should be fish exposed to sudden changes in the chemical composition of water.

Fish susceptible to the disease/disorder: