Effects of supplemental wild zooplankton on prey preference, mouth gape, osteological development and survival in first feeding cultured larval yellow tang (Zebrasoma flavescens)

Abstract

Yellow Tang, Zebrasoma flavescens, are a popular species in the aquarium industry. Currently, all Yellow Tang are collected from wild stocks, with collection in Hawaii accounting for the bulk of the individuals found in the trade. Although culture of this species has recently been successful, survival remains low and mass mortality events, particularly associated with the transition from endogenous to exogenous feeding, continue to be observed. Improving survival and gaining a more thorough understanding of the drivers behind early prey selection, such as mouth gape and osteological development, are of primary importance in advancing the culture of Yellow Tang. For the present study, a supplemental size-sorted mixture of wild zooplankton was offered in conjunction with and compared to the cultured nauplii of Parvocalanus crassirostris to determine the effect on survival. Prey selection was determined via metabarcoding. Osteological development was documented and mouth gape measured from 1 to 6 days post hatch to better determine appropriate prey types and size ranges. Survival was significantly lower in larvae fed cultured nauplii supplemented with wild zooplankton, 6.9% v. 18.5%. Regardless of the presence of wild zooplankton, larvae preferentially selected for P. crassirostris based on molecular determination of prey consumption. However, it is likely that protozoans were mostly excluded from this molecular analysis possibly due to the type of primer selected. Mouth gape height increased by approximately 100 μm and mouth gape width by approximately 55 μm, during the study period. Although no significant difference in growth was calculated between treatments, larvae receiving the wild zooplankton supplement diet were observed to grow at a slightly slower rate than larvae being fed only cultured copepod nauplii. The rate at which the mouth gape increased suggests that the currently cultured and utilized copepod nauplii may not be an optimally sized prey item shortly after first feed. These findings indicate that first feeding Yellow Tang larvae are capable of consuming larger prey at an earlier age than they have been offered in previous rearing attempts, but that the larvae may continue to benefit from the presence of less elusive prey items, such as ciliates or rotifers, due to their delayed osteological development. Osteological development was slow with very little ossification occurring by 6 days post hatch and only in those larvae fed solely cultured nauplii. However, their selection of copepod nauplii suggests that some aspect of this prey item is preferential to the first feeding larvae and may elicit a hunting response essential to initiating exogenous feeding.