Are Discus Fish Aggressive?

Discus fish are popular aquarium fish because they are large, colorful and not prone to hide. There are many species of discus fish available in the pet trade and they are usually not aggressive with other discus or with many other non-aggressive tropical fish species. But sometimes they can get aggressive. Individual discus fish may be more aggressive than others of the same species.

  1. Size

    • Generally, discus fish will harass fish that are much smaller than they are, even if the small fish is another discus. Having plenty of hiding spaces in plants, tubes or other decorations can help some harassed fish hide from any aggressive discus. But if the fish is small enough to fit inside of a discus' mouth, it will be eaten. Keep in mind that most discus grow to be 6 to 8 inches in diameter.

    Bottom Feeders

    • The best fish that discus get along with other than its own species are bottom feeders. These fish are too big for the discus to eat, do not compete for the discus' food and stays out of the discus' way. Walter's Discus Aquarium web page recommends plecostomus, upside down catfish, Kuli loaches, clown loaches, dwarf catfish and twig catfish as compatible tank mates.

    Spawning

    • The time when discus will be most aggressive to other fish or to other members of its own species is when they are spawning. The pair picks a territory and defends the eggs and newly hatched fry vigorously, even to the point of killing any other fish that gets too close. Pairs are best left together without any other fish to provoke them.

    Numbers

    • Discus tend to feel safest when they are in groups of at least four of the same species. According to the United Kingdom's Tropical Fish Centre, discus fish are most likely to attack each other when there are only three or less of them. A solitary discus will also menace the other fish. A minimum size tank should be 40 gallons in order to comfortably house four adult discus.

    Warning

    • According to the book "Discus Fish," discus will feel threatened by fish that normally swim fast, like danios or silver dollars. Discus are sensitive to the vibrations in the water that these constantly fast-moving swimmers produce. It's recommended to keep the discus separate from other species, with the exception of bottom feeders.