There is so far only one type of non-predator fish in The Blockheads. It has a square body with curved, vertical stripes and a generally diamond-shaped, broad tail fin. Fins stick out from either side which are most visible when viewing the creature head-on or if it's flopping around.
It generally resembles a common clownfish (amphiprioninae ocellaris).
Fish seem to swim idly in the water, appearing to undulate while doing so. They also emit bubbles, small, lightly-colored squares that quickly diminish and vanish as they ascend. Their bubbles can rise above the surface.
They will avoid a standing Blockhead and move away from a swimming one, so in shallow water can be herded. A Blockhead walking in very shallow water will typically be ignored. They will swim quickly away from a Blockhead that has struck them, moving faster than a swimming Blockhead. Sharks provoke no reaction.
When encountering the bait on the end of a cast fishing rod line, an interested fish will quickly move back and forth until it gets hooked and reeled in.
Fish will turn around if they encounter a vertical wall at least two blocks high. However, they will swim up and down diagonal walls.
In cold regions where freezing occurs, fish will tend to swim deeper as ice forms. Yet it's possible for a fish to become trapped in ice, in which case it will eventually despawn if not freed. They can also despawn in unfrozen water.
A fish dug free of ice (or, presumably, removed from water alive) will flop around on a block until it dies and despawns.
Despawning fish make a watery "blurp" sound. They have not been reported as dropping anything when they despawn for reasons other than a Blockhead's attack.
Fish can be killed by the usual means (hand or tool), but it's more efficient to use a fishing rod. At least eighteen (18) fish can be caught with one fishing rod.
A caught fish goes into inventory as raw fish meat.
Fish captured in a bucket can be placed where desired as a form of decoration.