The aim of this study was to determine the distribution of the mediator margins and marketing costs throughout the fishermen, brokers and retailers per one kilogram of commercially most preferred species in the sample of Istanbul province, Turkey. The primary data was collected with questionnaires conducted on brokers and the intense interviews with retailers. The most common commerce channel as fishermen-broker-retailer-consumer was examined. Marketing margins of fishermen and retailers active in fish marketing channels were calculated by examining the difference between monthly sales price and monthly purchase price at every stage in the study. The percentages of fishermen's income, brokers' income, marketing costs, retailers' costs and retailers' income within one kilogram of fish were varied between, 32.78%and% 54.84; 4.46% and 7.40%;2.56% and 4.42%;26.66%and48.02%, 6.67% and 12.04% respectively. The fact that; fishermen must sell their products through the cooperative to prevent low price formation during the auction and to reduce marketing expenditures was achieved. In order to increase producer income, it is very important to increase the amount of fishery products marketed through cooperatives by changing the brokerage system where fishermen market their products by borrowing.