Depending on what you are looking for I have a couple recommendations, no chains, and on the way back to Boston via the scenic route. Let me know if you want more info.
, West Rd., Temple off rte 45; no salt ever, healthy fish and plants handpicked by owner.Tanks not on a central filtration.
The Fish Bowl
, Milford, rte 101 on Milford oval; will custom order, carries salt and brackish fish as well as nice healthy selection of Africans.
Not exactly Concord but on the way