Why does one Fantail Goldfish chase the other?

Written by jason prader Google
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Why does one Fantail Goldfish chase the other?
Fantail goldfish are often bought as first pets for children. (Getty Thinkstock)

Fantail goldfish are part of the Carassius auratus family of fish and are a popular first purchase for those looking to start a collection. They are fairly easy to care for and should be kept within a temperature range of 13 to 21 degrees Celsius (around 55 to 70 degrees Farenheit). Chasing behaviour in fantail goldfish can have a number of causes from territorial aggression to playfulness.

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Despite their minute size, fantail goldfish require a lot of tank space to live comfortably. To choose the correct tank size for your goldfish, multiply the length of the tank by its depth (i.e. 22 x 14 = 308). Now divide this number by 30 (308 / 30 = 10.2). The result gives you the size of goldfish you can comfortably house in a water tank. In this case, you could have a fantail goldfish measuring 10 cm, or 2 measuring 5 cm each. If you restrict the size of the tank any further than these limits, fantail goldfish are prone to chase each other as they feel claustrophobic and are inclined to fight to gain more territory.

Playful activities

Fantail goldfish are similar to most other animals and set aside time for playful activities. Although the chasing may appear aggressive, in many cases it is simply playful and carries no threat. Observe your fantail goldfish to see if they are chasing one another (as in taking turns) or if one is continually menacing the other. If the former is true, it is very likely that it is harmless, playful activity.

Mating rituals

One fantail goldfish may chase another as part of a mating ritual. Typically, the male pursues the female goldfish in a display known as the spawning chase. The male chases the female and targets the female abdomen for several hours. When the female is prepared, she releases her eggs in batches which the male will then fertilise with its milt spray. A fantail goldfish in her prime can lay up to a thousand eggs.


Fantail goldfish, if deprived of sustenance for long enough, may turn aggressive and start to use each other as food sources by chasing and nibbling on one another’s flesh. If your goldfish are exhibiting such behaviour despite regular feeding, check you are using a high quality feed with the nutrients fantail goldfish require. Avoiding over feeding is also important as food debris can corrupt the cleanliness of the tank.

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