Species-transformation provisions allow fishers to convert quota of one species to that of another species at prescribed conversion rates. These provisions, along with other catch-quota balancing mechanisms, are meant to aid fishers in matching available quota to actual catch so that incentives to discard are reduced. In this paper, we use a bioeconomic model to examine how species-transformation provisions affect sustainability and profitability of a multispecies fishery. We base parameterization of the model loosely on management of the Icelandic demersal fishery, which currently employs one of the broadest implementations of species transformations. To represent fisher behaviour in each year, effort is allocated among two or three métiers, such that total profit for that year is maximized. Each métier represents a combination of three species’ catchability rates that define which species are targeted by each métier and how independent a species’ catch rate is from that of other species. Assumptions regarding the degree to which fishers can target specific species by shifting effort between métiers, as well as how relative profitability among métiers varies, are paramount to understanding more generally how fishing regulations such as species transformations can be expected to change fishing patterns. This constraint depends not only on how strongly associated species catches are within a métier but also on relative species abundance and what alternate métiers are available.