Why Would One Goldfish Bite the Tail Off of Another One?

Many consider goldfish to be the perfect pet. They are easy to care for and a delight to watch as they glide serenely around their watery environment. Misconceptions about these animals include thinking they are stupid and complacent creatures. But goldfish are just as complex as any other pet and require the right care, conditions and situation to live happily and thrive. When a fish's needs are not met, it may exhibit unusual behavior including aggression towards companions.

  1. Environment

    • Most goldfish are cold-water creatures, though some species prefer their environment slightly warm. A substantial rise in water temperature, caused by close proximity to home heating or direct sunlight, can stress them into aggressive behavior. While done with the best intentions, introducing new accessories such as plants, rocks or structures can disorientate or confuse these sensitive creatures. Sudden illumination, such as switching on a room lights from darkness or opening morning curtains, may startle fish into hostile actions through shock or fear.

    Diet

    • Some pet owners may provide generous quantities of food such as large pinches of fish flakes, assuming it will last for several days. But goldfish tend to eat for only a few minutes at a time, and untouched food is likely to sink and rot. Providing the wrong type of food or irregular feeding times can lead to hunger. This may provoke violent activity when starving fish have to forage, or begin to view companions as a food source.

    Territorial

    • Colorful goldfish swimming blissfully around a bowl is a common sight but developing fish may outgrow their home. With overcrowding comes the possibility of competing for necessities including space and food. Physical attack on another is a forceful way to gain the majority of scarce resources. The natural instinct to mate can also instigate a battle as rivals compete over a female's favors. Many species of animals exhibit a hierarchy, or pecking order, with the challenger dominating the others through hostile actions or force.

    Considerations

    • Aggressive behavior in a goldfish or other pet requires swift action to determine the reason and eliminate the cause. Exploring the possibilities of problems arising from care, conditions, relationship or environment is the first step. If no obvious cause is found, expert advice from professional organizations, breeders and pet store or aquarium specialists is advisable. In extreme cases, separating problem fish may be the only answer to avoid the risk of serious injury or fatalities.