What is that!
Oh, it's my lunch (They remove a sandwich with eyes from the end of their fishing line)
...
Do you want some?
— A conversation between a local fisherman and a foreign traveller
Origins
The sandfish was created many years ago as the result of a malfunctioning spell. A young mage of the South Islands, left unsupervised by their teacher, attempted to conjure themselves some lunch when their spell backfired. They were unable to control the direction of their magic and it entered the ocean, causing an explosion of sandwich looking fish (commonly referred to as Sandfishes). Although multiple attempts were had at removing this species from Iastarene's oceans, they quickly multiplied and nowadays have become a native species.

Sandfish by Frod0_baggins
Appearance
Sandfishes are sandwich-like in nature but with large eyes at the front. They also have small side fins and a tale fin which often appear to look like lettuce or some other sandwich filling. The filling of each sandfish varies, although they are most commonly ham or cheese alongside a vegetable of some form. Although they spend their lives underwater, once taken out of the water they are quick drying and their bread-like outside does not go soggy.
Habitat
Sandfishes are native to the southern isles of Iastarene, particularly around the ports of Dentallie. They prefer shallow, warmer, water so are often caught by fisherman who fish from the beaches. They have so far not been spotted outside of Iastarene and, therefore, it has been concluded that they prefer not to travel too far from home.
Uses
Sandfishes are often a common snack for busy fisherman as they are easy to catch and don't need to be cooked. Aside from food, they have no other notable uses. There have been very little studies into how exactly they live or survive, and their existence is purely because of magic. Because of their origins in magic, it is now illegal to be caught with a sandfish due to laws outlawing magic and it's by-products. This initially sparked debate as sandfish are not technically magical themselves, however, this law is now widely accepted.
It is cute sandwich.