This paper studies the role of middlemen in open-access fisheries and how the organization of the supply chains affects resource exploitation and the level and distribution of economic rent. Imperfect competition among middlemen can help ensure that fish stocks are not depleted, which is typically the case in open-access fisheries with competitive markets. Middlemen with market power can also induce higher economic rent for the supply chain in total, but these rents mainly benefit the middlemen. The supply chains of inshore anchovy and offshore skipjack tuna fisheries in Vietnam are used as empirical examples. The analysis shows that in the anchovy supply chain, the middlemen have insignificant market power and the stock is being overexploited. In the skipjack tuna supply chain, the middlemen have oligopsony power and the stock is higher than the level that produces maximum sustainable yield.