Determining Ingestion of Microbound Diet Particles by Mud Crab, Scylla serrata, Larvae

Abstract

This study evaluated 14C-labelling as a tool to investigate the suitability of microbound diet (MBD) particles for the various larval stages of the mud crab, Scylla serrata. The results showed that S. serrata larvae held in seawater containing 14C leachate from 14C-labelled MBD particles (after MBD particles had been removed) did not contain levels of 14C above background. However, dead S. serrata larvae held in water with 14C-labelled MBD particles had a significantly higher 14C content than background even after thorough washing. They suggested that MBD particles trapped on the body of crab larvae cannot be completely washed off, and they represent a source of error that needs to be corrected when using this technique to determine ingestion of MBD particles by crab larvae. Consequently, a control treatment consisting of dead larvae held with 14C-labelled MBD particles was used to correct larval ingestion data in subsequent experiments. To determine larval ingestion of MBD particles, each larval stage of S. serrata was fed 14C-labelled MBD over a five-hour period and their radioactive contents were determined hourly. MBD particles were readily ingested by all larval stages of S. serrata. Ingestion of MBD particles increased with larval development with megalopa consuming more than three times the amount of MBD than Zoea V and more than ten times that of Zoea IV larvae. Ingestion of MBD particles by Zoea I declined after four hours, whereas ingestion by Zoea II, III and megalopa did not differ significantly over the five-hour feeding period. Zoea IV and V showed greater levels of MBD ingestion after four and five hours than after one hour. The present results suggest that the time to reach maximal ingestion, as indicated by the time to achieve maximum larval 14C content, for Zoea I, II, III and megalopa is one hour, but is greater for Zoea IV and V. The results of this study allow fine-tuning of a technique with great potential for investigating aspects of the nutrition of S. serrata larvae and indicate clear potential for developing successful MBD for them.