Is 'piscantur necesse est' a correct adaptation of the well-known Plutarch maxim 'navigare necesse est'? I would like to say "angling is necessary", but I am unsure whether it remains correct after my modification.
In Latin, "fish" is piscor, -ari, -atus sum, a first conjugation deponent verb.
The form you use, piscantur, is third person plural. It means "they fish."
The original phrase is a later Latin translation of Plutarch's Greek translation of what Pompey said, presumably in Latin: "πλεῖν ἀνάγκη, ζῆν οὐκ ἀνάγκη."
Navigare is active infinitive: "to sail." The equivalent form of piscor is piscari. You thus have:
Piscari necesse est.
If you want a gratuitous addendum, here's how Plutarch would have said it in Greek: