fishing is a verb or verb-ing
It can be either. Where is your sentence?
It can be either:

"I like fishing": (strictly speaking ambiguous, but verb is the more salient interpretation ("I like to fish"). Noun interpretation can be forced by adjectival premodification, as in "occasional fishing". Likewise "Fishing is prohibited", verb preferred but noun can't be excluded ("Even occasional fishing is prohibited"). It can only be a noun in "The fishing here is good" (note the definite article "the"). And only a verb in "I am fishing", (progressive aspect).

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