It can be either. The plural of salmon may be either salmon or salmons.
The word "salmon" is both singular and plural.
The noun 'mice' is the plural form of the singular noun 'mouse'.
The singular noun is "louse" and the plural noun is "lice."
noun that are plural in form but singular in meaning
The noun children is the plural form of the singular noun child.
The noun 'circus' is a singular noun.The plural noun is 'circuses'.
The noun juggler is a singular noun. The plural noun is jugglers.
The singular noun is trio; the plural noun is trios.
The singular noun is Tuesday.The plural noun is Tuesdays.
The noun 'orchid' is a singular noun, a word for one.The plural noun is 'orchids'.
salmons is the plural way but salmon is the singular way
The noun mailbox is the singular form; the plural is mailboxes.