How about a custom-made fish tank that fits his exact specifications? You could work with a local fish store or aquarium shop to design a tank that complements his taste in fish and home decor. Alternatively, you could plan a day out fishing together, followed by a seafood dinner at a fancy restaurant. Either way, it shows that you value his interests and are willing to share in them with him.
Or you can get him a star map with the date of your anniversary.
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.