I thought about it again and came to a solution:
-Sparos (nom. sing.) bēgra (acc. plural) ipradas?
-Sparos (acc. sing.) bēgra (nom. plural) ipradis?
So we just need to change ipradas to ipradis, because the trout is plural. But if it would only be one trout, then the two sentences would be identical. So the problem is that both "sparos" and "bēgor" have the same form in nominative and accusative.
With dragons you could differentiate:
-Sparos zaldrīzī ipradas?
-Sparos zaldrīzes ipradas?