Choose Your Preferred Size of Fish

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Choose Your Preferred Size of Fish

Discus Sizes

The size of Discus fish can range, but are classified as a medium fish and are expected to be 6-10”.  Because of their shape, they are as wide as they are long. With that in mind, aquarium size must be considered from start to finish of the fish’s lifecycle. It is important for keeper’s to remember that Discus are social fish and enjoy being a part of a group. However, with that in mind, up to 3-5 Discus thrive in a 50-60-gallon tank. A larger tank will be needed to house more fish.

For first-time Discus keepers, the starter size may be misleading for just how large the fish will get at full maturity by the age of 2.5 years. The following chart provides a breakdown of general growth:

Age of Fish

Size in Inches

2 Months


4 Months


6 Months


9 Months


12 Months


18 Months


24 Months


It is important for keepers to provide adequate aquarium space so that Discus can grow to their fullest potential. The age as well as the size of the fish at maturity will greatly impact the overall are of the fish.

  • Starter– Starter fish are generally very small and range from 2-2.5” in size. With such a small appearance, it may be very tempting to get several starter fish to make the appearance of a tank seem more robust. However, it is critical for collectors to realize that in a few months the Discus will be much larger and will need space to grow. Not only will limited space alter the ability for the fish to thrive, but it could lead to a failure to adapt to the aquarium.
  • Small At full maturity, some Discus remain small. This can be an issue if there are much larger Discus in the tank. It is best to keep Discus sizes within 1” of each other in order to reduce aggression and maintain tranquility in the tank. Small discus typically range from 2.5-3.5″.
  • Medium– Medium Discus are generally about 3.5-4.5” in length. Experienced keepers have identified this as a good size because it is typically not too large to introduce starter fish nor too small to live with larger Discus. This size maintains the 1” rule for co-living.
  • Large– As mentioned, some Discus run a bit large. Generally speaking, this is any fish that reaches 6” at maturity. Keepers should make adequate changes to the aquarium if the size of the fish causes overcrowding. While many collectors have indicated that 3-5 fish fit comfortably in a 50-gallon tank, larger fish will require that some fish are removed from the tank. Large discus typically range from 4.5-6″.
  • XXL Monster– In some instances, Discus can grow to be especially large. Typically, this means that the fish is over 8”. While a large size certainly indicates that the fish has been able to thrive, it is critical to move overly large fish from a tank that houses much smaller fish. This will reduce issues with food and space and ensure that each fish is thriving to its fullest potential. XXL Monster discus exceed 6″ in size.

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