Species profiles
How difficulty is rated
Every species profile rates the fish from beginner to expert, as a rough guide to how much you'll need to get right to keep it well. The rating is worked out from seven of the fish's needs, such as tank size and water, so if one of those looks wrong on a profile you can tell us there.
The five ratings
Each of the seven measures below scores the fish from one bar to four. We average the bars, and the average sets the rating unless one of the needs under "What can raise a rating" sets a higher minimum.
- Beginner
- under 1.5 bars
- Most measures are at one bar. There's little to plan for beyond giving it a tank of the right size.
- 44
- Easy
- 1.5 to 2 bars
- Most of its needs are routine, but one or two take planning, such as a group of its own kind or a larger tank.
- 422
- Moderate
- 2 to 2.75 bars
- Several things need sorting out before you buy the fish. Which ones varies by species, and could be the water, the tankmates, the space or a mix of them.
- 1,156
- Difficult
- 2.75 to 3.5 bars
- Demanding on most measures, so most of its needs go beyond what an ordinary community tank offers.
- 176
- Expert
- 3.5 bars or more
- At or near four bars on almost every measure, so the whole setup has to be planned around this one fish.
- 1
The number beside each rating is how many species have it. Another 21 can't be rated until more is known about them.
The seven measures
More bars means more to plan for. The words beside each reading are the ones you'll see in the Difficulty panel on a profile.
Space
The minimum tank length given on the profile. If there isn't one, we go by how big the fish grows.
- small tank
- a tank under 45 cm, or an adult under 6 cm
- medium tank
- a tank of 45 cm or more, or an adult of 6 cm or more
- large tank
- a tank of 90 cm or more, or an adult of 12 cm or more
- very large tank
- a tank of 150 cm or more, or an adult of 25 cm or more
Water
Every fish starts on one bar, and each of these needs adds another, up to four. A fish that needs soft, acidic water held within a narrow pH range is at the top of the scale.
- needs soft water
- a hardness of 5 dGH or less
- needs acidic water
- a pH of 6.5 or lower
- needs alkaline water
- a pH of 7.8 or higher
- needs a steady pH
- pH held within a range of 1 or less
- flexible
- none of the above
Temp
A typical heated tank runs at 24–26 °C. A fish that needs it warmer or cooler than that, or held within a narrow range, scores more bars, up to four.
- needs warm water
- a minimum above 26 °C
- needs cool water
- a maximum below 24 °C
- needs cold water, no heater
- a maximum of 20 °C or lower, a bar on top of cool water
- needs a steady temperature
- a range of 4 °C or less
- needs a very steady temperature
- a range of 2 °C or less
- flexible
- none of the above
Diet
Scored only when a fish needs something specific from its food, and each of these is three bars. Any other diet is left as unknown.
- needs wood to graze
- no meaty foods
- won't eat dried food
- needs snails to wear down its teeth
Temperament
How an adult behaves towards other fish.
- peaceful
- territorial
- fights its own kind
- eats smaller fish
- needs a tank of its own
Social
Whether it should be kept with others of its own kind, and how many.
- fine alone
- best in a pair
- needs a few of its own kind
- needs to be in a group
- needs a large group
Compatibility
Whether it can share a community tank with other species.
- fine with others
- choose tankmates carefully
When a measure is unknown
Some profiles are missing information, such as a tank size or a pH range, because it has never been written down for that species or hasn't been added yet. A missing measure shows as unknown and is left out of the average. We never count it as one bar, because then the less we knew about a fish, the easier it would look.
One bar and unknown mean different things. One bar means the profile gives the need and it's an easy one to meet. Unknown means nothing is recorded, and tells you nothing about how easy the fish is.
A species needs at least 3 of the seven measures recorded to get a rating. With fewer, its profile says "Not enough data to rate" and shows whichever measures are known.
Diet is unknown on most profiles. Most diet sections recommend a mix of dried and live foods. That could mean the fish eats almost anything, or only that nobody has written down what it needs, so we can't score it either way. Diet is scored only when a profile names one of the specific needs listed above.
If you can fill in something missing from a profile, please add it and tell us where it comes from, whether that's a book, a paper or your own experience with the fish.
What can raise a rating
A few needs make a fish harder to keep however easy it is in every other way. A fish that needs an enormous tank is a big undertaking even if it's peaceful and undemanding about water, but averaged with six easy measures that one need could leave it rated beginner. So each of these sets a minimum rating on top of the average, and some of them, such as a well-established tank or strong current, aren't among the seven measures at all. If the average comes out higher, the average stands. If it comes out lower, the fish is rated at the minimum. The profile lists them under "Other demands".
- Needs a well-established tank, as it's sensitive to the swings in water quality common in a newly set-up oneat least moderate
- Needs to be kept at 27 °C or warmerat least moderate
- Needs strong or very strong currentat least moderate
- Needs a very large tank, scored four bars on Spaceat least moderate
- Needs a tank at least 2 m long, or grows to 50 cm or more where the profile gives no tank sizeat least difficult
A hardy fish isn't rated any lower for being hardy. When one of these needs lifts a rating above its average, the profile gives the reason in a line such as Rated moderate because it needs a well-established tank and stable water.
If a rating looks wrong
A wrong rating usually comes from a measure that's wrong or missing. Use the "Something here wrong?" link on the profile to tell us which measure, what it should say, and your source for it.
A moderator can also set a rating by hand for a fish that's harder or easier to keep than its measures show. The profile then says why.