Old English fisc, from Proto-Germanic *fiskaz (cf. Old Saxon, Old Frisian, Old High German fisc, Old Norse fiskr, Middle Dutch visc, Dutch vis, German Fisch, Gothic fisks), from PIE *peisk- "fish" (cf. Latin piscis, Irish iasc, and, via Latin, Italian pesce, French poisson, Spanish pez, Welsh pysgodyn, Breton pesk).
Fish story attested from 1819, from the tendency to exaggerate the size of the catch (or the one that got away). Figurative sense of fish out of water first recorded 1610s.
Plural fish or fishes
Any of numerous cold-blooded vertebrate animals that live in water. Fish have gills for obtaining oxygen, a lateral line for sensing pressure changes in the water, and a vertical tail. Most fish are covered with scales and have limbs in the form of fins. Fish were once classified together as a single group, but are now known to compose numerous evolutionarily distinct classes, including the bony fish, cartilaginous fish, jawless fish, lobe-finned fish, and placoderms.
Other and more pressing matters to attend to; more important things in prospect: Anyway, we've got bigger fish to fry/ Tell him to relax, we've got bigger fish to fry