SHAU Kei Wan and Aberdeen typhoon shelters are black spots for illegal fish trading, officials have said.
The Agriculture and Fisheries Department said about 20,000 tonnes of marine fish were believed to be sold illegally each year rather than through the official body, the Fish Marketing Organisation.
Fisheries officer Edward Wong Cheuk-kee believes half of the catch is sold to other fishermen in international waters or to neighbouring Chinese ports such as Shekou.
''We estimate a portion of the other half of the catch - the more valuable fish - are marketed illegally near Hong Kong's typhoon shelters.
''The remaining low to medium-price fish are then sold through our wholesale markets. This has led to a decline in the commission we charge, which is based on the wholesale price of the fish,'' he said.
Mr Wong said illegal traders had a close relationship with the Hong Kong fishermen involved.