How does the speaker personify the fish? Why does Bishop have the speaker revise her initial statement about the fish?

First of all, the speaker personifies the fish by giving him gender. She refers to him using the pronoun "his". Even though we know fishes can not convey emotions, she uses adjectives to describe his expression such as "battered and venerable", or "his sullen face".

As she observes closer, she begins to empathise with the fish and finally sets him free.