You stand before the BBEG as they deliver their grand speech. They get to line seven of paragraph five on page three when you decide to tell them to shut up in the most effective way possible. Too bad all you have is a bag of fish product. You shrug and decide that's good enough for what you're gonna do. You cast a spell as you throw the bag, and suddenly the BBEG stops talking. They look stunned and insulted. "Did you just throw a fish at me!?" They snarl at you. Yes, yes you did. 

As you cast the spell you proceed to conjure and throw a single fish in the direction of your enemy. As it makes contact with them you utter words of contempt for that creature. Make a ranged spell attack against this creature.  This creature must make a wisdom saving throw equal to your spellcasting modifier. Upon a fail they take 2d4+2 bludgeoning and psychic damage. Upon a success the creature only takes 1d4+1 bludgeoning damage. If the fish makes contact with the creature they will have disadvantage against everyone but the caster as they are too distracted with the idea that that person has the audacity to hit them with a fish. 

At higher levels:; if you cast a spell at levels higher than level 1 for every level the spell is cast at you will gain one fish, and at levels above five the size of the fish increases by one size category, as well as the damage increasing by 2d4+2 bludgeoning and psychic damage per size category. If the size of fish would cause the creature to be pushed or knocked prone they must make a strength saving throw and a wisdom saving throw. 

It can be used in any situation on anyone or anything you want. The text is just flavoring for comedic affect. If you wanna throw a fish at a wall you can. I don't know why you would, but you did it so clearly there's a reason.