Natural Fish Dynamics - A Mod for Factorio

Fish breed on their own in their natural habitat.
On supported planets chunks can spawn fish if:
- There is at least 2 Fish
- There is enough water.

Fish will reproduce based on a normal distribution.
Highest chance of reproduction when water is half-full with fish.

Supported Planets

Nauvis
Gleba - Check tips how to import fish on Gleba
Aquilo - Fish import is also needed (Note: Won't work with mods that void items in ammonia ocean)
Pelagos
Lignumis
Rabbasca

All settings are runtime-global and can be changed in-game at any time.

Breeding Limit – Maximum number of fish allowed per full-water chunk before overpopulation stops breeding (default 128, 16–512).
Breeding Cycle – How frequently breeding attempts occur (default "normal"; options from "ultra-fast (×10)" to "ultra-slow (÷10)").
Breeding Chunk Scale Divisor – Controls overall breeding frequency across the map. Lower values = faster fish population growth. Higher values = slower growth with lower UPS impact (default 1200).
Breeding Max Chunks Per Tick – Maximum chunks the mod can check per tick per surface. Higher = faster breeding on very large maps but higher UPS usage. Lower = better performance (default 32).
Fish Litter Size – Determines how many fish are born at once from a successful breeding (default 1, 1–16).
Enable Breeding on [Planet] – One toggle per planet (Nauvis, Gleba, Aquilo, Pelagos, Lignumis, Rabbasca). All default to enabled.

Disabling breeding on a planet you don't plan to use fish on skips all breeding checks for that planet, saving UPS with no side effects.

You can catch and release fish by dropping them in water with 'Z'
Watch video

Planet - Pelagos
Planet - Lignumis
Planet - Rabbasca
Dredgeworks: Frozen Reaches (DISABLE mod setting: 'Aquilo ocean destroys items' - or importing fish will not be possible)