Length-weight relationships were estimated for 19 fish species in sargassum beds of Gamak Bay: Aulichthys japonicus, Pseudoblennius cottoides, Pseudoblennius percoides, Ditrema temmincki, Acanthogobius lactipes, Chaenogobius heptacanthus, Cryptocentrus filifer, Pterogobius elapoides, Pterogobius zonoleucus, Hyporhamphus sajori, Hexagrammos agrammus, Rudarius ercodes, Lateolabrax japonicus, Pholis crassispina, Pholis nebulosa, Scomber japonicus, Sebastes inermis, Ernogrammus hexagrammus, and Takifugu niphobles. Samples were caught by surrounding net at depths of <7 m between November 2007 and June 2008. The most abundant families were Gobiidae (26.3%), Cottidae (10.5%), and Pholididae (10.5%). Estimates for parameter b of the length-weight relationship (W=aLb) ranged between 2.491 and 3.354.