The successful and selective feeding of larval fishes in the low-latitude open ocean: Is starvation an insignificant source of mortality?

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Historical interest in understanding the larval stage of high-latitude fishes has provided extensive insight into feeding-related processes that can influence larval fish mortality. However, the feeding dynamics of larvae that occur in lower latitudes, especially those that primarily inhabit oceanic waters, is notably limited. From monthly sampling across the Straits of Florida (SOF) over two years, we acquired data on the feeding ecologies of 21 taxa of fish larvae in order to elucidate levels of feeding success, as well the degree to which this subset of the larval fish community relies upon specific zooplankton prey types. Larval taxa examined included billfishes, tunas, mackerels, and seven families of coral reef fishes. All but one taxon examined for gut contents (total n = 3138) had feeding incidences near 100%. Additionally, gut evacuation was rapid and occurred in ~3 hr, indicating successful and frequent prey consumption. These observations, in conjunction with the fact that larvae withstand a nightly non-feeding period (10- 14 hrs in low-latitudes), point to the possibility that fish larvae in these waters experience low or even negligible levels of starvation mortality, although additional efforts specifically addressing this possibility are needed. Furthermore, diets of larvae were taxon-specific and often extremely narrow, illustrating very selective feeding among a high diversity of available zooplankton prey. Two notable characteristics of the diets of these larvae were high reliance upon appendicularians by several taxa and the prevalence of piscivory, which appears to be exhibited by over 30 species of scombroid larvae that occur in the SOF.