From the tourist harbour in Cat Ba, there is a nearby fishing village (about 30 minutes boat ride away).
Villagers live on board house boats with mini fish farms in front of their houses. I'm not sure if you can board the house boats for a view of the fish being bred there.
Lan Ha Bay
Some guide books will not differentiate between Halong Bay and Lan Ha Bay, but the latter is the bay closer to Cat Ba island, with views similar to Halong Bay (but apparently not as dramatic).
Also, most tourist boats will not go to Lan Ha Bay although most kayaking trips do take place there.
In my opinion, I wouldn't know how to distinguish where the boundaries for the two are. I don't really care as long as I get to enjoy the peace and solitude of the bay.
Meandering through the islets, hearing the insects and coming up close face-to-face with some cliff faces in the serenity is really relaxing.
At low tide, many lagoon entrances are exposed adding to the mystery and beauty of the surrounding landscape.