What does the cryptic crossword clue "A smart-alecky fish? That ain’t right (5,5)" mean?

The wordplay uses a charade (building blocks). ACUTE (synonym="ACUTE") + ANGLE (synonym="‘fish’, verb") = ACUTEANGLE The answer is ACUTEANGLE.

A smart-alecky fish? That ain’t right (5,5)

Guardian Cryptic #29461 | 7 Down | 2024-08-14 flower