Noun
The plural form of the noun catfish, a word for a living thing, is catfishes.The noun catfish, a word for a food substance, is an uncountable noun.
No, the noun 'catfish' is a commonnoun, a general word for a species of fish.A proper noun is the name of a specific person, place, or thing; for example:James "Catfish" Hunter, American baseball playerCatfish Stream Avenue, Las Vegas, NVCatfish Cove (restaurant), Oklahoma City, OK
That depends on the species of catfish unfortunately. Corydoras are common freshwater aquarium catfish and can live from 10-15 years.
Bullheads are not sold commercially, but are common catfish across North America.
Very common. Bristlenose are easy to breed and will do so if conditions are OK for them.
Unless it is a localized indigenous name, (common in the American South) they are known (properly) as "Blue Catfish", a specific species of catfish.
Common
Common noun
The white catfish is not an endangered species, common over much of the U.S.
common
Pea is a common noun, and peas is the plural...still a common noun.