Why Do Aquarium Fish Die?

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Aquarium fish are a very popular pet as they can add beauty and serenity to your home, be a fun pet and provide a soothing scene to enjoy. However, many new aquarium fish owners are saddened to find their fish dead shortly after purchasing them and with no apparent reason. There are several reasons for the high mortality rate found with aquarium fish.

  1. Unhealthy fish

If your new fish dies relatively quickly, there may be a chance that it was unhealthy when it was purchased. Fish owners should review information regarding signs of illness prior to shopping for a new fish. Some symptoms of distress or illness could include:i

  • abnormal swimming patterns
  • gasping, labored breathing, or abnormal swimming
  • loss of appetite
  • changes to the body shape or contours
  • loss of coloration
  • the presence of cysts, sores, blood-stains, or ragged patches

Unfortunately, if you purchase a fish that is in poor health, there is often little or nothing that can be done to prevent its death and even providing an optimal environment to promote health may not ensure that it lives.

  1. They are overfed

Watching aquarium fish feed is one of the most exciting parts of being an owner. This is a time when they are most active and engaged. However, this can cause a tendency to overfeed them. Understanding how much food is required for your fish is much harder than it sounds, and many new owners assume that because they are still eating, or still acting hungry, that they must need more food. But this isn’t necessarily true, as they really only usually need a few mouthfuls daily (usually only the amount that can be consumed in 1-2 minutes), and only need to be fed once in a 24-hour cycle. If severely overfed, spoiled food may accumulate in the tank and be another risk factor in the fishes’ health.ii

  1. Exposure to untreated tap water

It’s easy to think that any freshwater fish would be able to survive in regular tap water, but this usually contains chlorine and chloramines, which can prove lethal to fish. This can be avoided by treating the water with a water conditioner. Prior to purchasing a fish, consult with an expert on the type of conditioner that would work best in your aquarium.iii The water may also have nitrates and ammonium contaminants. These are usually balanced by natural bacteria, but this can take time so the levels should be checked regularly prior to adding new fish.iv

  1. Rapid water or temperature changes

Once a healthy environment is established in a tank, it should be carefully monitored. Any changes in water must happen slowly as changing it quickly will disrupt the chemistry of the tank and will cause the fish to go into shock, causing death. The same is true regarding drastic temperature changes. Most fish can adapt and survive within a range, but if there is sudden, drastic temperature changes, it may make the fish more susceptible to illness and can even cause death.v It is recommended that all water be given time to slowly acclimate to the tank temperature using small bags to prevent temperature shock for the fish.

  1. Unexpected toxins

Another common cause of premature death in aquarium fish may be due to the introduction of unexpected toxins into the tank. Even in very small amounts, these chemicals can be fatal to fish. These toxins are usually introduced when someone reaches into the tank without washing their hands first. Things like bug spray, cleaning chemicals, lotions, perfumes and even soap can quickly kill aquarium fish even in tiny amounts. For this reason, it is very important to wash your hands with an unscented, non-antibacterial soap before reaching into the water. You should also invest in a high-quality lid that will prevent anything from entering the tank that may be sprayed nearby.vi

  1. Deterioration of tank water

Establishing a healthy water balance for aquarium fish to thrive in is not an easy task, and it is certainly not one that is complete once the goal is initially reached. The pH level of the tank must constantly be monitored as even the slightest change may have an adverse effect on its inhabitants. As mentioned earlier, ammonium and nitrate may exist in tank water. This is because fish produce these as natural waste, and in high levels exposure to them can be lethal. Many experts recommend having a filter running continuously that will remove these wastes. While bacteria will break down these toxins, and that is how it is commonly treated in natural environments, there is typically not nearly enough of it in a tank environment to keep up with the amount produced by the fish. Under most normal circumstances, fish will only survive 6-8 weeks in a tank when ammonia and nitrite are not removed. It is also recommended that the tank water is tested periodically for ammonia, nitrite, nitrate and pH using a liquid water test kit to ensure that the filter is operating properly. If it is a saltwater aquarium, there are additional steps required to ensure the proper level of salt, or salinity, is maintained.vii


Author: Rikki Roehrich

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