In this paper, I investigate aquaculture externalities on fisheries, affecting either habitat, wild fish stock genetics, or fishing efficiency under open-access and rent-maximising fisheries. This is done with a Verhulst-Schaefer model of fish population-dynamics and production, coupled with a simple aquaculture production model. Externalities are modelled by letting carrying capacity, the stock's intrinsic growth rate, or catchability coefficient in the fishery depend on aquaculture production. The different externalities can give totally opposite results on steady-state fishing effort, yield, and stock, even for only negative externalities. With a catchability externality, increased unit cost of fishing effort implies reduced aquaculture production to maximise benefits to society under reasonable assumptions. Resource allocation between the industries is analysed under three different coastal management regimes: 1) aquaculture has a primary right of use; 2) joint management of aquaculture and fishery; 3...