THE government-run Fish Marketing Organisation lost 30 per cent of its potential commission - $18 million - to illegal marketing last year. As a result of fishermen by-passing official markets, the organisation's commission on last year's sales was cut to only $40 million. Agriculture and Fisheries Department officials admitted high-priced fish, such as garoupa caught in the South China Sea, were no longer sold in the seven official wholesale markets. Assistant Director (Fisheries), Richard Yip Shui-ming, confirmed some of the local trawlers' catch was sold outside Hong Kong, due to economic pressure on the fishermen. But an illegal trade thrives in the typhoon shelters, even those where the official markets are located. The department believes the seven per cent commission on sales was a strong incentive for fishermen to cheat. A South China Morning Post team watched pre-dawn illegal exchanges near the Aberdeen market last week. Men off-loaded boxes of fish onto the shore from a vessel. The boxes were then loaded onto waiting lorries heading towards various retail fish stalls. Fisheries officer Edward Wong Cheuk-kee said the tonnage and value of fish going through official channels had dropped. Last year, 63,300 tonnes of marine fish worth $572 million were traded through the wholesale markets compared with 67,600 tonnes worth $647 million in 1992 and 75,800 tonnes worth $680 million in 1991. Mr Yip said many fishermen sold their catch outside Hong Kong to maximise profit. ''The first thing they gain from such an off-shore sale is time. It allows them to get back to the fishing zone quicker,'' he said. New Territories Fishermen's Association chairman So Moon-cheung said triad activities such as controlling prices in the fish markets, not the seven per cent commission, continued to be the main reason traders resorted to illegal sales. ''Triads in the official wholesale markets have been forcing traders to sell the produce to them at a lower price so that they can gain from the difference between the buying price and the market price,'' he said. ''Because of the threats, fishermen have switched to selling their produce illegally once they arrive in Hong Kong.'' Shamshuipo assistant district commander (crime), Detective Superintendent Nick Roberts, said a lack of witnesses had made investigations into triad involvement difficult. ''Triads are controlling transport and hire of coolies [labourers]. They are doing a legitimate business but just not allowing competition. It's a monopoly in which they dictate the price of fish,'' he said. Mr Wong said fisheries officers were liaising closely with police to ensure fishermen and traders had a chance of fair trading. The department will commission a consultancy study on market operations in a bid to attract more fishermen back to the traditional markets. Mr Yip said the study would address existing problems as well as projecting future needs. The president of the Hong Kong and Kowloon Floating Fishermen Welfare Promotion Association, Keung Yin-man, welcomed the review. and hoped the markets would operate systematically without a monopoly. ''It is a question of how to implement the recommendations which relate to the future of the industry,'' he said.