Planet Zoo 2 launched on October 13, 2026, and the question I have seen more often than any other this week is not about habitats, money or crashes. It is about a menu that looks broken.

Open the Zoopedia entry for the Boeseman's Rainbowfish and the two gender rows read 1 to 0. Not a range like 1 to 4 — 1 to 0, on both rows, with nothing in the game explaining it. In the r/PlanetZoo thread about it the guesses ranged from "the game doesn't sex fish" to "it's a bug" to "you can only keep one". None of them is right, and the answer was sitting in Frontier's own data the whole time.

One boolean explains it

Every species record in the Zoopedia export carries a per-species flag called shoal_fish. For the Boeseman's Rainbowfish it is true.

When that flag is set, the species is stocked as a shoal rather than as a sexed pair, so there is no male/female split to print and both gender rows collapse instead of showing a range. It is not a bug, and it does not mean "maximum zero".

The obvious follow-up is how common it is — and because pz2tools.wiki is generated from a full export of the launch Zoopedia, that is a count rather than a guess:

20 of the 130 launch species are shoal species. All 20 are fish (class: Actinopterygii).

The 20, grouped by the water they need

Freshwater — Lakes & Rivers (7): Boeseman's Rainbowfish, Blunthead Cichlid, Common Rudd, Brown Trout, Clown Loach, Giant Gourami, African Tigerfish.

Reef (7): Clown Anemonefish, Schooling Bannerfish, Longfin Batfish, Blue and Gold Fusilier, Palette Surgeonfish, Yellow Tang, Bluespine Unicornfish.

Open sea (2): Pacific Sardine, Pacific Bluefin Tuna.

Mixed biomes (4): Threespot Damselfish (Mangrove + Reef), Indo-Pacific Sergeant (Open Sea + Reef), Indian Ocean Oriental Sweetlips (Estuarine + Reef), Golden Trevally (Estuarine + Reef).

The same 20 with water type, biome, size and barrier grade side by side are on the aquarium species page.

Three things that fall out of the list

1. Fifteen of the twenty are also Exhibit animals. They carry both HabitatAquarium and Exhibit in the enclosure field, which means you can show them in a walk-in glass exhibit before you commit to a full tank build. The five that are aquarium-only are Longfin Batfish, Pacific Sardine, Indian Ocean Oriental Sweetlips, Golden Trevally and Pacific Bluefin Tuna — which is exactly the set of shoal species you cannot cheap out on.

2. The eight fish that do show a gender range are the big-bodied loners. The roster has 28 fish: the 20 shoal species above, plus eight that are stocked as individuals — Dolphinfish, Giant Grouper, Red Lionfish, Blackspotted Puffer, Sailfin Snapper, Ocean Sunfish, Clown Triggerfish and Humphead Wrasse. Those are the entries where the sexed-pair menu is the right interface, so the contrast between the two groups is a useful sanity check on the flag.

3. Two of the six Deluxe animals are shoal fish. The Deluxe Edition adds Longfin Batfish and Blue and Gold Fusilier on top of Axolotl, Golden Eagle, Golden Lion Tamarin and Great Hammerhead. So if you bought Deluxe, a third of those six new animals will show you 1 to 0 as soon as you open their entry.

The practical rule

If a fish shows 1 to 0 on both gender rows, do not assume the menu is broken and do not assume the animal is bugged. Check whether the species is a shoal species — the species page carries the answer next to biome, enclosure type and barrier grade. If it is, the planning question that actually matters is which other species share its water, and that is a biome + enclosure check you can run pair by pair on the compatibility chart.

Boeseman's Rainbowfish is a good example: eight species share both its biome and its enclosure type, six of those pairings are confirmed group-living by Frontier's own Zoopedia text, and two are unverified. So it is a fish that should be in a shared freshwater tank — which is the opposite of what 1 to 0 suggests if you read it as a limit.

Where the numbers come from

Everything above is a field in the same source-verified export: 130 species, 1,221 cohabitation pairs, biome, enclosure type, barrier grade, conservation status and the shoal_fish flag. It is mirrored on GitHub with a Zenodo DOI so the numbers are citable, and the filterable animal list is generated from it rather than maintained by hand. If you find a species where the flag and the in-game UI disagree, that is worth writing up — but every 1 to 0 case I have checked lines up exactly with the flag.