flat fish
That's called the flatfish!
Better question: why are there evolutionary niches allowing flat fish to thrive? Three answers, although you shouldn't consider me an authority: 1. Flounders lay flat on the bottom, and flatness allows them to be less conspicuous. 2. Flatness minimizes shadows on the ocean floor, thus aiding in stealth. 3. In coral reefs, a flat body and a long nose allows fish to get at food inside coral heads. In each of these three scenarios, it's not hard to understand how flatter fish would be more successful -- and therefore more likely to reproduce.
You format the hard disk
Hard Coral is not a fish but, some small fish live in hard coral.
4 toes and one thumb behind it but it is very hard to see clearly.
yes,it is hard to clean out a pet fish's filter
yes it is hard
flat and hard
The fish you are referring to is likely the pufferfish. When threatened, pufferfish can inflate their bodies with water or air to appear bigger and deter predators. They have spines on their skin that lay flat when not inflated but become prominent when they puff up.
If you hit the fish hard enough yes.
You buy it...
A hard blow with a flat object.