A quota is the allowable number or amount of fish that can be harvested in a commercial or recreational fishery.  This is a regulatory strategy to limit harvest.  They are set each fishing season based on allowance for sustainable harvest (e.g., see Maximum Sustainable Yield).

Image credit: Fisheries New Zealand, mpi.govt.nz)

In certain commercial fisheries, quotas are essentially equivalent to a “share” in a fish stock.  These Individual Transferable Quotas (ITQs) can be bought and sold and entitle the owner to a given proportion of the Total Allowable Catch (TAC) for a fishing season.(fishionary.fisheries.org/quota).