Aquarium Compatibility Guide

Quick answer: Aquatic compatibility in Planet Zoo 2 follows the same cohabitation rules as land animals, with one hard split first — freshwater species and saltwater species cannot share a tank. Per-species compatible pairs are not published in a shared Frontier list — read each species' in-game Zoopedia entry.

What's confirmed

Cohabitation applies to aquatic species — the same compatibility system Frontier says is "more significant" in the sequel (Cohabitation)
Freshwater and saltwater are separate environments — a species' water type decides which tank it can go in
Compatibility drives stress vs. enrichment — compatible tankmates enrich each other's welfare; incompatible ones cause stress

The freshwater / saltwater split

The first compatibility check is water type. The full confirmed aquatic roster, with each species' type, is on the Aquatic Animals page. Mixing a freshwater species into a saltwater tank — or the reverse — is not a valid combination.

What's still waiting

Specific compatible pairs, per-species water temperature and salinity tolerances, and mixed-species tank rules are not published in a shared Frontier list. The in-game Zoopedia flags compatibility per species.