Abstract
Southern bluefin tuna (SBT), Thunnus maccoyii, are a long-lived, migratory pelagic species that spawn south of the Java Sea off the northwestern coast of Australia. Identification of T. maccoyii based on larval pigmentation has been challenging due to high pigmentation similarities with other larval tuna species and changes in pigmentation occurring throughout the larval period. Larval T. maccoyii were collected off the northwest coast of Australia between the January – March spawning season. Genetically identified T. maccoyii larvae were flexion staged. An updated “pigment wheel” and taxonomic key were developed by surveying 21 pigment locations and through caudal fin pigment spot analysis as presented in Nishikawa & Rimmer (1987). Seven pigment locations showed ≥ 70% pigment presence when combining all flexion stages together; however, the pigment presence by flexion stage showed variability for these locations. Caudal fin pigment patterns deviated from the original pigment wheel with the inclusion of zero dorsal pigment spots and separation into flexion stages. Larval T. maccoyii exhibit diagnostic pigmentation in the caudal fin and likely in other locations, though more work is needed to confirm for these locations; nonetheless, the taxonomic key description of T. maccoyii was still able to be updated. Future work will be expanded with respect to other larval tuna species from the same collection to better understand the early life history of these fish. Basic understanding of early life history can support the development of management strategies focused on protecting larval and juvenile tuna.