Tardeo, near the AC market. Starters 200/-, fish 250/- to 375/-, rice 90/- [7/01].
After Only Fish became famous, the tiny old place in Shivaji Park was no longer adequate. The restaurant has now moved to a more expensive avatar in Tardeo, and changed its name.
The food is excellent and nearly worth the price. The Dab Chingri is a spectacularly well presented variant of a much loved traditional dish. The Doi Machch and the Shorshe bata Machch are probably the best you can get this far to the west of the Bangladesh border.
The ubiquitous Rosogolla should be passed over for the less well-known desserts. Rosogollar Payesh is a good fallback if you can't bring yourself to try something new.
The service is excellent if you speak Bengali.