I imagine if he were offering it back to you (sort of like re-gifting), it might feel more meaningful, rather than you reclaiming it for yourself. A relational process rather than a unilateral one. If the two of you were able to discuss the significance of the fish (the meaning is obviously not just about the fish itself) and what the giving, receiving, placing of the fish symbolizes then the offering it back to you could open up further work again. For example, the fish might be understood as parts of you and those parts belong with you and not others. At the moment it all sounds locked in rejection, shame, misunderstanding instead of being able to explore what's happening relationally and in your process. He seems to be thinking of it all very literally.