Larval distribution of the ocean sunfishes Ranzania laevis and Masturus lanceolatus (Tetraodontiformes: Molidae) in the Sargasso Sea subtropical convergence zone

Abstract

Abstract Sunfishes or Molidae are a rarely encountered family within the teleost order Tetraodontiformes and most details of their reproductive biology including times and places of spawning and their larval ecology are rather unclear. Spawning of two species of Molidae was suggested in the Sargasso Sea before, yet comprehensive data on larval distribution from this area or elsewhere have never been published. Here we report on the abundance and size distribution of 383 sharptail mola (Masturus lanceolatus) and slender sunfish (Ranzania laevis) larvae, present novel information on their larval growth and development and test correlations with prevailing hydrographic data. Only 18 mostly larger Masturus larvae were caught evenly distributed over the study area and with no obvious hydrographic preferences. We conclude that there was no active spawning of M. lanceolatus in the area during the time of the cruise. In contrast, Ranzania larvae were caught primarily inside and south of a thermal frontal zone with increasing abundances toward warmer surface layers in the southeast of the study area. Due to the consistent presence of young Ranzania, it can be assumed that spawning activity was ongoing throughout the month of April, 2015. Our findings confirm the Sargasso Sea as a spawning area for R. laevis.