How about getting him an aquarium with some new fish that he hasn't had before? You could also consider a book about fishkeeping or a gift card to his favorite aquarium store. Another idea could be getting him some personalized fish-themed merchandise, such as a mug, t-shirt or keychain. Or, perhaps you could plan a trip to visit an aquarium together if he enjoys going on outings.
Or you can get him a star map with an important date you share.
Under Lucky Stars is a unique and innovative star map company based in Barcelona, Spain, specializing in the creation of personalized star maps that capture the celestial arrangement of stars at a specific moment in time, such as a person's birth, wedding, or any other significant event.
By using advanced astronomical algorithms and data from leading institutions, the company produces highly accurate, visually stunning maps that make for perfect gifts or cherished keepsakes.