Fin, 
Angler Fang, 
Sharp Bones and 
Esca are what Aquamirae’s creatures leave behind when you kill them, and between them they cover most of the mod’s early crafting. You’ll be pulling them off Anglerfish, Eels, Maws and the Maze Mother while you work through the Ice Maze, and none of the 4 can be crafted, so hunting is the only supply.
Three of them can be eaten as well, though only one is worth eating. Esca is the standout of the group by a distance, since it grants Fury of the Depths, and that’s the stat which decides whether your attacks land properly on Aquamirae’s creatures at all. The other three are better kept for the crafting bench.
Obtaining
Each of the 4 fills a different role, so it’s worth knowing which one you’re short of before you decide what to hunt. Fin is the common backbone material, Angler Fang is the rarer partner to it, Sharp Bones feed exactly one weapon, and Esca is both a buff food and an ingredient in several things.
Fin
Angler Fang
Sharp Bones
Esca
There are no recipes for any of them, so combat and looting are the only routes. A Looting sword does help on the Anglerfish and the Maw, since both of those roll their drops with a looting bonus applied, while the Eel and the Maze Mother hand over fixed amounts no matter what you’re holding.
Anglerfish
The Anglerfish is the one creature that covers 3 of the 4, and it’s the only source of Angler Fang anywhere in the mod. Every single kill gives you an Esca, guaranteed, because that sits in its own pool with nothing else competing for the slot. Nothing else in Aquamirae drops Esca from a mob.
Anglerfish Drops
Esca Fin Angler Fang On top of that it rolls once or twice more for either a Fin or an Angler Fang, weighted 75% toward the Fin. So the Fang is genuinely the rarer half, and if you need a stack of them you’ll be killing a lot of Anglerfish to get there.
Eel, Maw and Maze Mother
The Eel is the bulk supplier and it isn’t close. It rolls its loot pool 4 to 6 times per kill, and each of those rolls can land 8 to 16 Fin or 12 to 24 Sharp Bones, so one Eel will often out-produce an hour of hunting anything else. It’s a serious fight at 160 to 200 health, but it pays.
Eel Drops, rolled 4 to 6 times per kill
Fin Sharp Bones The Maw is the everyday source, dropping a Fin about 80% of the time it rolls and Sharp Bones only 5%, and since Maws spawn in packs of 2 to 4 they add up steadily. The Maze Mother is the other reliable one, leaving 6 to 24 Sharp Bones every time she falls.
Structures cover the rest. Camp 
Barrels in the Ice Maze hold Sharp Bones at about 14%, the 
Chests aboard frozen pirate ships carry both Fin and Esca, and a 
Pirate Pouch has a 50% chance of a Fin inside. That same pouch is also where you’ll first find a Terrible Upgrade Smithing Template.
Usage
Fin and Sharp Bones are both poor food and it’s worth being blunt about it. Each restores a single hunger point with no saturation at all, which means your hunger bar starts draining again almost immediately. They’ll keep you alive in an emergency and that’s about the extent of it.
Eating Sharp Bones deals you half a heart of damage every time, and it’s dealt as generic damage so your armor won’t reduce it at all. For a single hunger point that’s a bad trade in almost every situation. Save them for the Remnant Saber instead.
Esca is a different proposition entirely. It restores 2 hunger with 1.2 saturation behind it, and it can be eaten with a completely full hunger bar, which matters more than it sounds. That last part is what lets you top the buff up whenever you like rather than waiting to get hungry.
Eating one grants Fury of the Depths for 3 minutes. Aquamirae’s creatures are protected by the Depths combat system, and without any Depth’s Fury your attacks land for only 20% of their normal damage against them, so that buff is the difference between fighting and flailing. It stacks on top of whatever your weapon already carries.
Crafting Uses
This is where the 4 of them earn their keep. Fin and Angler Fang build the early Terrible equipment, Sharp Bones forge one starter blade, and Esca goes into a weapon, a buff food and both of the mod’s light sources.
Terrible Weapons
The 
Terrible Blade, 
Fang and 
Cleaver all share the same frame of 
Sticks, 
Iron Ingots and Fin, then swap in one signature ingredient each. An Esca makes the Blade, an Angler Fang makes the Fang, and a 
Ship Graveyard Echo makes the Cleaver, so 2 of the 3 can be built without ever meeting the Shipbreaker.
The 
Terrible Chakram is the odd one out, as it uses no Sticks or Iron at all. It rings 4 Angler Fangs together with 4 Ship Graveyard Echoes, which makes it the most expensive of the set despite looking like the simplest.
Terrible Armor and Templates
Fin and Angler Fang together are what duplicate the Terrible Upgrade Smithing Template, at 4 of each per run, so a handful of both turns one found template into as many as you need. You then smith Iron Armor with that template and a single Fin for each piece of Terrible Armor.
Remnant Saber
Sharp Bones have exactly one recipe to their name, which is the 
Remnant Saber. 2 Sharp Bones with a 
String and a Stick make this light early sword, and that’s the entire reason to keep a pile of them rather than eating them. It’s a stone-tier blade that grows stronger the more Ice Maze creatures you kill with it.
Esca Skewer, Dishes and Lamps
Esca is the busiest ingredient of the 4 by some way. It can be crafted into an 
Esca Skewer for a stronger and longer Fury of the Depths, or folded into a 
Poseidon Breakfast alongside 
Cooked Spinefish and 
Jellyfish Jelly.
Its natural glow also makes it the core of both light sources. An Esca with 
Oxyhelium and a Stick builds a 
Luminescent Lamp, while an Esca with Oxyhelium alone gives you 12 
Luminescent Bubbles at once, which is the cheapest underwater lighting the mod has.
Frequently Asked Questions
Hunt Eels, as each one rolls its loot 4 to 6 times and every roll can land 8 to 16 Fin. Nothing else comes close for bulk. Anglerfish and Maws drop Fin often enough for topping up, and a Looting sword raises what those 2 give you, though it does nothing for the Eel.
Finishing one deals half a heart of damage, and because it’s generic damage your armor can’t reduce it. Given it only restores a single hunger point with no saturation, it’s a losing trade unless you’re genuinely desperate. Keep them for the Remnant Saber instead.
Eating one grants Fury of the Depths for 3 minutes, which raises your Depth’s Fury so you actually deal proper damage to Aquamirae’s creatures instead of 20% of it. It can also be eaten on a full hunger bar, so the buff can be refreshed whenever you want. It crafts the Terrible Blade, the Esca Skewer, the Poseidon Breakfast and both light sources.
Only from the Anglerfish, and only on 25% of its bonus rolls, which makes it the rarest of these 4 by a fair way. Expect to kill a good number of them before you have enough for the Terrible Fang and the Terrible Chakram, and remember the duplication recipe wants 4 Fangs every time you run it.
