Brightly Coloured Coral Reef Cleaner Fish
Puzzle 15 of Celtic Mythology Hard Pack
Question is: Brightly Coloured Coral Reef Cleaner Fish
and the answer is: WRASSE
Word Meaning:
WRASSE — Any one of numerous edible, marine, spiny-finned fishes of the family Labridae, of which several species are found in the Mediterranean and on the Atlantic coast of Europe. Many of the species are brightly colored.
Definitions from Wiktionary.