This is a coastal embark because the waves and mist are real nice but the weather ended up being worst than expected and the ocean froze. This provided an opportunity to dig a 2x3 shaft through the ice down to a cavern dozens of Z-levels below. Then we waited until May and suddenly it all thawed and behold this bounty from the sea:

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Schools of fish, including anchovy, herring, hake and one seahorse; now herring has the massive schools property but neither hake nor anchovy do. We thought the fish were pulled because of the draining effect but no, after a short time they escaped the map and can't be found in the cavern below... What was that?

  • From experience or game mechanics, is it typical to find schools of fish right after some ocean thaws during Spring or was this related to the sea being drained, were the fish curious or what?
  • How come anchovy and hake were schooling despite seemingly not having this property (massive schools)?
  • Is there a channel size which would guarantee the fish being pulled down (I used 2x3) i.e. would create a strong enough pull to stop the fish from escaping, if that's what happened (not seeing anything in the raws for each fish which would allow me to figure that out, if that's even possible) i.e. do fish have speed?

1 Answer 1


Anchovies, herrings, hake, and seahorses are all vermin, which means that they don't really travel and just sort of spawn where the game thinks they ought to live. So they didn't escape the map agains the drain effect, they just vanished back into the ether that formed them. No amount of draining would trap these tiny vermin in place. True creatures like carp or zombie giant whales would be susceptible to being pushed around by water; however, they would also need to migrate in from the edges of the map after the ocean thawed, rather than simply being spawned into existence.

As for school size, the massive schools description of herring is just flavor text; it has no effect on actual gameplay. The actual amount that spawn is controlled by the [CLUSTER_NUMBER] tag in the creature (or vermin) definition. Both anchovies and herrings have [CLUSTER_NUMBER:50:100] so they will spawn in similar-sized schools. Hake have [CLUSTER_NUMBER:25:50] so they will tend to spawn in smaller groups. It looks like Toady forgot to include a [CLUSTER_NUMBER] tag on the seahorse, so it gets the default of [CLUSTER_NUMBER:1:1], and spawns all by itself.

Why you suddenly saw a big school of each of these animals: probably because the ocean thawed all at once and the game said to itself "oh man, look at all this unpopulated water! I better get some vermin in there, quick!" I admit I'm guessing on this point.

  • Thanks! I should have paid more attention to the info from the vermin article on the wiki and you're right they just sort of spawn and you can't see them on the units screen etc. Your guess is as good as mine as to why the fish were there. The cluster behavior was in the raws even in 40d but it's the first time I've seen so many fish in the game. Anyways, cheers!
    – user76919
    Commented Apr 20, 2018 at 4:57

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