After 'To jest' you use nominative case. Why would you use accussative?
Examples of nominative cases:
-To jest duża ryba - This is a big fish
-To jest wysoka góra = This is a high mountain
Examples of accusative cases:
-Widzę dużą rybę - I can see a big fish
-Widzę wysoką górę - I can see a high mountain
Sorry what i meant a bove is either that way or i actually typed in this fish is tasty which is definitely also a correct translation to english and it didnt accept it and mark me down. Correct gramatical translations would be this is a tasty fish or this fish is tasty... This is tasty fish just makes no sense and seems be a very rudimentar translation of the sentence literally word by word.