These fish are all residents of the water, I know. They are pleasure-seekers for just a few hours, I know.

This couplet is a profound observation on the nature of temporary pleasures. The fish, being permanent residents of the water, symbolize a life lived within a specific environment. But the poet observes that their 'extravagance' or joy is only for a fleeting moment. It suggests that no matter how beautiful or natural a joy seems, its duration is always limited. It's a gentle reminder about the transient nature of earthly delights.