Current knowledge status on myctophids’ diversity in the Southwest Atlantic Ocean

Myctophids (Family Myctophidae) are among the most common and abundant mesopelagic fishes in the world’s oceans, characterized by ca. 250 species grouped by 33 genera. Despite their globally recognized ecological relevance due to their role in pelagic trophic webs, in the Southwest Atlantic Ocean off of Argentina (33º S - 56º S), myctophids are still understudied, and the available information about these fishes is scarce and fragmented.

During the second half of the last century, a series of surveys was conducted by foreign research and fishing vessels along the continental shelf off of Argentina and its adjacent waters, driven with the aim of studying the main pelagic and demersal resources of the Argentine Sea. Some of these cruises have been pivotal in addressing the first assessments of myctophids’ species diversity and distribution patterns in the region. In the past decades, myctophids have been captured mainly as by-catch aboard fishing and research vessels; nonetheless, there is currently a lack of ecological studies that specifically target these mesopelagic species.

The aim of this study was to provide a comprehensive review of current knowledge of the Family Myctophidae in the Southwestern Atlantic. We analyzed myctophids’ diversity patterns in the region, updating with non-published data and new records from 1,248 fishing trawls collected during 10 cruises (1978-2023) along the Argentine continental shelf, the shelf break, and part of the oceanic domain between 33º and 56º S.

A total of 79 myctophid species belonging to 24 genera were identified, with distinct distribution patterns: 22 tropical, 13 subtropical, 4 temperate, 13 subtropical convergence, 15 subantarctic, 7 antarctic, and 5 widespread. Based on the new data, our results revealed that myctophids’ species-richness is higher in the oceanic zone north of 40° S (Brazil--Malvinas Confluence zone) and lower at the shelf break, with no species present on most of the continental shelf.