Goldfish
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.
Goldfishes There is no plural for goldfish. Goldfish itself is plural. Example: Hey Bob, can I see that goldfish you caught? Example2: Hey Bob, can I see those goldfish you caught?
The goldfish's
There is no plural form. Do and Do not are verbs
The plural form of the noun dog is dogs.The plural possessive form is dogs'.Example: All of the dogs' collars have a tag imprinted with their name.
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "I" is "we."
The plural form of "was" is "were."
"Groceries" is the plural form of "grocery."