rivulus vs killifish

rivulus and killifish both are nouns.

Word	Noun	Adjective	Verb	Adverb
rivulus	Yes	No	No	No
killifish	Yes	No	No	No

As nouns, killifish is a hypernym of rivulus; that is, killifish is a word with a broader meaning than rivulus:

rivulus: found in small streams of tropical America; often kept in aquariums; usually hermaphroditic
killifish: small mostly marine warm-water carp-like schooling fishes; used as bait or aquarium fishes or in mosquito control

rivulus (noun)	killifish (noun)
found in small streams of tropical America; often kept in aquariums; usually hermaphroditic	small mostly marine warm-water carp-like schooling fishes; used as bait or aquarium fishes or in mosquito control