Signs of stress in your aquarium.
A stressed fish behaves differently from how individuals of this species normally behave. When keeping fish in an aquarium for several weeks, you will notice that each species has a characteristic behavior (which is why keeping fish in an aquarium is so interesting!). Some fish are usually always near the water surface, while others, on the contrary, stay near the bottom. Some fish are continuously in motion, while others remain motionless for a long time. A deviation from their normal behavior usually indicates a stress state.
• If a fish stays near the surface, gasps for air, and has rapid breathing, this is one of the signs that there is not enough oxygen in the water. Possible causes of low oxygen concentration include insufficient water circulation, toxic substances that have damaged its gills, high levels of ammonia or nitrites, and so on.
• The fish refuses to eat or does not eat as actively as before.
• Fish constantly hide and are difficult to spot. Possible causes: aggression from other fish, insufficient number of hiding places for the fish to feel relatively safe.
• The fish has frayed fins, open wounds that do not heal. Possible cause: aggression from other fish. Usually, minor fin damage and wounds heal quickly. If this does not happen, the fish’s immune system is breaking down.
• The fish gets sick (parasites, bacteria, etc.). Of course, the disease itself is the main problem. But in most cases, the immune system of a healthy fish protects it from infection. Thus, the disease is a sign that the fish is under stress (or has been until recently).
If you notice that a fish is experiencing stress, eliminate its cause immediately. The fish are completely under your care and protection, and their stress is usually the result of your actions (or inaction). First of all, you should check the water. Check the concentration levels of hydrogen, ammonia, nitrite, and nitrate. If something is wrong, fix the situation. If everything is fine here, test the equipment. What is the water temperature, is the heater working properly? Is everything okay with the filter, is it coping with the load or does it need to be replaced? Has anything been spilled into the aquarium? Is the water clean, or is it cloudy or colorless?
If one of the inhabitants is terrorizing other fish, move the troublemaker. If a pair of Cichlidae has decided to settle down and is clearing space for itself by trying to get rid of other inhabitants, relocate the newly formed family or all the others.
If the fish is severely stressed (swimming at the surface and gasping for air, lying at the bottom and not moving, or darting around the aquarium), do not hesitate – toxic substances have entered the water. It does not matter whether it was a cleaning aerosol or something else. If you observe any of the above signs, immediately transfer the aquarium inhabitants to more suitable conditions.
If the danger is not too great and death does not threaten the small residents, perform a 50 percent water change, making sure beforehand that the new water is completely suitable for the fish. If there is a suitable container, you can move your pets, provided you have no doubts about the optimal water quality and the absence of hostility from other inhabitants. Act immediately – if you don’t hurry, you may lose your favorites.
The main source of stress, besides a “rebellious” fish or a newly formed pair, is a poor environment. A weekly twenty percent water change (maximum every two weeks) will help you prevent stress in your pets. Do not forget that you are the indirect source of all your pets’ anxieties, and it is only in your power to provide them with a calm and happy existence.
How many fish can be kept in an aquarium?
Stress and its impact on fish health. What is fish stress? 
