Fish Ponds Coming to Stardew Valley in Update 1.4
Though players can certainly turn these ponds into a decorative feature dotted around their farms, Stardew Valley fish ponds are meant for making money.
They'll act like aquatic chicken coops, letting players raise as well as collect fish and roe (fish eggs) that can then be sold. Barone mentioned "other products" on top of fish and roe, but apart from some suspiciously eggy looking things simmering in nearby kegs, there's no indication what else fish ponds might help players accomplish.
From a fish(y) perspective, adding ponds and letting players harvest them is a fairly big step for the game. Up to now, fish could only be caught, then sold or used in recipes — or "gifted" to townsfolk players didn't really like.
It's also worth noting this is just a small part of the 1.4 update, which Barone has previously said would include a wide variety of updates and improvements.
Keep in mind, too, that initially, fish ponds and the entire 1.4 update will be for the game's PC version only. Console versions are still waiting to get version 1.3, with Barone citing various technical issues Microsoft and Sony are working to resolve. The same version discrepancy applies to the mobile port, too, including the recent Android release.
Fish ponds and 1.4 or not, we still count Stardew Valley as one of the best farming games in the field right now.