Can one tuna species breed with another from a different geographic location (Atlantic with Pacific or Southern bluefins)?

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David, from Sweden, asked us: Can one tuna species breed with another from a different geographic location (Atlantic with Pacific or Southern bluefins)?

Fernando de la Gándara from the Spanish Institute of Oceanography answered:

Atlantic (Thunnus thynnus) and Pacific bluefin tuna (Thunnus orientalis) were considered subspecies of the same species until 2003. Although they don’t coexist in the same geographical areas, cross-breeding is certainly a possibility. It may also happen with Southern bluefin tuna (Thunnus maccoyii). In this case, T. orientalis and T. maccoyii do coexist, but hybridization must be very rare, because their spawning grounds don’t overlap.