"fish which lives or burrows in mud," c. 1500, from mud (n.) + fish (n.).
Entries linking to mudfish
mud n.
late 14c., mudde, "moist, soft earth," cognate with and probably from Middle Low German mudde, Middle Dutch modde "thick mud," from Proto-Germanic *mud- from PIE *(s)meu-/*mu- [Buck], found in many words denoting "wet" or "dirty" (source also of Greek mydos "damp, moisture," Old Irish muad "cloud," Polish muł "slime," Sanskrit mutra- "urine," Avestan muthra- "excrement, filth"); related to German Schmutz "dirt," which also is used for "mud" in roads, etc., to avoid dreck, which originally meant "excrement." Welsh mwd is from English. The older word is fen.
Meaning "lowest or worst of anything" is from 1580s. As a word for "coffee," it is hobo slang from 1925; as a word for "opium" from 1922. Mud-puppy "salamander" is by 1855, American English; the mud-dauber wasp was so called by 1856. The children's mud-pie is attested from 1788. Mud-flat "muddy, low-lying ground near a shore" is by 1779. Mud-room "room for removing wet or muddy footwear" is by 1938.
The expression clear as mud (that is, "not clear at all") is by 1796. To throw or hurl mud "make disgraceful accusations" is from 1762. To say (one's) name is mud and mean "(one) is discredited" is recorded from 1823, from mud in obsolete sense of "a stupid twaddling fellow" (1708). Mud in your eye as a toast is recorded from 1912, American English.
fish n.
"a vertebrate which has gills and fins adapting it for living in the water," Old English fisc "fish," from Proto-Germanic *fiskaz (source also of Old Saxon, Old Frisian, Old High German fisc, Old Norse fiskr, Middle Dutch visc, Dutch vis, German Fisch, Gothic fisks), perhaps from PIE root *pisk- "a fish." But Boutkan on phonetic grounds thinks it might be a northwestern Europe substratum word.
Popularly, since Old English, "any animal that lives entirely in the water," hence shellfish, starfish (an early 15c. manuscript has fishes bestiales for "water animals other than fishes"). The plural is fishes, but in a collective sense, or in reference to fish meat as food, the singular fish generally serves for a plural. In reference to the constellation Pisces from late 14c.
Fish (n.) for "person" is from 1750 with a faintly dismissive sense; earlier it was used in reference to a person considered desirable to "catch" (1722). Figurative sense of fish out of water "person in an unfamiliar and awkward situation" attested by 1610s (a fisshe out of the see in the same sense is from mid-15c.). To drink like a fish is from 1744. To have other fish to fry "other objects which invite or require attention" is from 1650s. Fish-eye as a type of lens is from 1961. Fish-and-chips is from 1876; fish-fingers from 1962.