The study was carried out monthly between April 2000 and December 2001 on the seagrass and/or sandy bottom in shallow waters of Erdek Bay (Sea of Marmara, Turkey).  Samples were collected using 35 m long beach seine. Fish samples were identified, measured and weighed. The length-weight relationships of juvenile and adult specimens of 36 fish species were investigated. The parameters a and b were calculated by functional regression, as was the coefficient of determination (r2). r2 values were higher than 0.950 for 27 species in the list, while only one species was lower than 0.80. The exponent b ranged from 2.282 to 3.741.