Iron golems attack fish, squid and dolphins. This screenshot was made with no mods enabled except for Terrestria and Fabric API

This is fixed in today's Terrestria releases. Thanks for the issue report.

Can you please provide logs? I don't think Terrestria does anything to change the behavior of the golems so in order to look into this I definitely need more details, particularly the versions of everything and ideally any log info that might provide a hint.

@gniftygnome here's prismlauncher's log: https://mclo.gs/SnVSepH
i don't know if there's any other logs i can get

That looks like complete logs, yup. Much to my dismay it's not got anything interesting logged, but at least I know the versions of things now. Do you even need to be in a Terrestria biome for this to happen? Probably not?

nope, the screenshot is in plains and i've seen that happen in other vanilla biomes too

Uh. We were certain you would like how easy this makes farming bonemeal? ;)

I've got no idea what is happening there yet but I can reproduce it so I've got what I need to try and figure it out. Thanks,

Oh I think I found it (right where I looked first). It looks like I was accidentally using interface injection to turn WaterCreatureEntity extenders into Monster implementers. Sloppy work on my part earlier this year I guess. I'll get it tested and then release an update.