After a throrough scouring of the city, Hellonanjing has investigated two pet and flower markets thus far.
The first and most easily accessible is a small back lane behind FuzioMiao temple. There are only a couple of flower shops with slim pickings. There are animal suppliers as well. They've got a good stock of pure bred puppies, a few cages of haggard looking street cats, a couple of dudes hawking Chinese birds and parakeets, and a decent tropical fish vendor.
In sum, Fuzimiao market is grim and limited.
A better option, for flowers at least, is the Longjiang Flower Market. They've got a large selection of tropical and summer plants, gardening tools, and soils (although not much in terms of liquid fertilizers).
Prices are reasonable, and the vendors are easy to communicate with.
They have one large aquarium shop as well, with a slightly smaller selection than the one at Fuzimiao (goldfish, oscars, neons, etc).