fish
Insects are not a species. Insects are are a class of invertebrates within the arthropod phylum. That is like asking if mammals are the most numerous species. Your question needs to be refined. Are you asking if insects are the most numerous class of animal? Most numerous species of living thing? Or perhaps you are thinking of a specific species such as monarch butterfly (Danausplexippus).
Fish species
It is a declarative sentence.
The degree of comparison is superlative.
Osteichthyes, the bony fish class, has over 30,000 species.
The positive degree of comparison is used. (That it, no comparison is made.)
Bacteria, the most numerous organisms on Earth , are unicellular organisms - just had this question on a homework
Fish
Pizza
planet
fish, birds and ants
Man