It is both. The plural form is the same as the singular. This is generally true of the word 'fish' on its own or used as a suffix. I don't think 'fishes' as a plural is incorrect, but it isn't commonly used.
The plural of goldfish is goldfish. It is the same as the singular.
Goldfish
practitioner is singular (plural practitioners)sofa is singular (plural sofas)satellite is singular (plural satellites)clips is plural (singular clip)dentist is singular (plural dentists)dollars is plural (singular dollar)article is singular (plural articles)magazines is plural (singular magazine)laminator is singular (laminators is plural)radios is plural (singular radio)
singular and plural
Singular: book / Plural: books Singular: cat / Plural: cats Singular: child / Plural: children Singular: foot / Plural: feet
Are is plural. "Is" is singular. For example, "There is a glove on the chair". That is singular. "There are gloves on the chair". That is plural.
"Has" is singular, e.g. He has, she has. "Have" is plural, e.g. They have, we have. The exception is "I" - e.g. I have.
The word team is singular; the plural form is teams.
Who may be singular or plural.
This is singular. These is the plural form.
These is plural, this is singular
'These' is the plural form of 'this'.