Answer:

guppies

Answer	Crossword Clue
GUPPIES	Popular aquarium denizens
GUPPIES	Aquarium fish
GUPPIES	Rainbow fish

GUPPIES	Tropical fish.
GUPPIES	Pet fish.
GUPPIES	Rainbow fishes

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.