The fish are poikilotherm vertebrata. This mean that their body temperature changes with environment temperature (water temperature). In other words, the fish can't keep a warmth, they can't adjust their body temperature and their metabolism activity relative to temperature fluctuations of their environment. The fish are adapted to water temperature changes in certain limits but these changes can't be rapid. Then we have to deal with thermal shock.
Too low water temperature causes that fish body fluids circulate slowly and it falls into a state of torpor. Then it stops eating - in extreme cases water can crystallize in fish body and it could consequently freeze in consequently. The tropical fish which aren't adapted to these conditions often catches cold and then their immune system is weakened. So they are sensitive to any secondary bacterial, viral and parasitic infections – especially fungus disease. Repeated temperature decreases lead to serious consequences – fish dwarfing, gills damaged etc.
Too high water temperature causes meaningful changes in personality of the fish, especially among no-tropical fish. They can be aggressive, very active, even hyperactive. Jump in temperature of 6°C causes serious cardiovascular impairment and it is cause of toxins poisoning. Also, this case leads to secondary infections – especially gas bubble disease and oxygen deficiency disease.
The fish much better endure low water temperatures than high water temperatures.
- lack of appetite
- clamped fins
- apathy, languid and slow movements
- the fish hang under the water surface or they are close the heater
- gill covers deformations
- forceful swimming, hyperactive, rocking from side to side
- attempts of jumping out from aquarium
- aggression
- loss of colours
- eye turbidity
- bubbles on the skine
We should gradually increase/ reduce water temperature when we notice a misstatement – about 1°C per hour. Too rapid changes cause thermal shock of the fish. We need intense to aerate the water in this same time. Next we must remove the cause this situation. The immune system of the fish is weakened, so we should use adequate vitamin preparations and water treatment conditioners (e.g. Tetra AquaSafe, Sera Aquatan, JBL Atvitol, etc.).