Faster way to get to Tung Choi St (Fish St in HK)...
Take MTR to Prince Edward MTR station, exit B... exit at the one leading to Allied Plaza...immediately after exiting look to the left and cross the road,turn right,walk straight until the end where you have to left turn...the first shops start there
Other marine specialty shops worth mention in HK...they are not in the main fish area and quite far from most hotels...but I feel worth the trip if you have time:
Polaris Aquarium
Take the tram that goes toward Shau Kei Wan...the tram line runs through almost the whole HK island... just look out of the window and you will see it on the left...good general marine shop....lifestock generally very good,well quarantined and sometimes rare things
Blue Castle
Take MTR to Hang Hau MTR station...exit B1 and look for the way towards La Cite Noble or "Sun Bo Seng" in Cantonese...it's a small housing estate and the shop is right at ground floor...quite new so nothing spectacular yet...but the equipment they use is more up to date and livestock quite good...they seem quite knowledgeable too...
website: www.bluecastleaquarium.com
Hope this helps