One-year rope-grown mussels (Mytilus galloprovincialis Lam.) with a mean length of 37.6+/-0.52 mm and live weight of 5.02+/-0.28 g were collected from fish farm mooring ropes and cultured in cotton or nylon socks in a long-line system in Sinop, Black Sea. The growth of the mussels, water temperature, salinity, chlorophyll a, seston and particulate organic matter were monitored from July 1997 for eleven months. Shell length and live weight were high from May to October when the temperature was 13degreesC-25degreesC. Growth decreased during late autumn and winter due to the low temperature and food availability. A significant and positive relationship was found between particulate organic matter, shell growth and live weight. At the end of the experiment, shell length reached 59.89+/-0.93 mm in the cotton socks and 57.81+/-0.88 mm in the nylon socks, while live weight reached 19.42+/-0.91 g in the cotton socks and 16.89+/-0.76 g in the nylon. Harvestable production was lower in the cotton (4.1 kg/m) than in the nylon socks (8.7 kg/m). Meat yield was high during spring and early summer and significantly and positively correlated with chlorophyll a, particulate organic matter and seston. In the light of these results, recommendations for mussel culture in the long-line system are given.