Influence of binder type on leaching rate and ingestion of microbound diets by mud crab, Scylla serrata (ForsskcEl), larvae

摘要

Microbound diets (MBD), composed of nutrients held within a matrix or binder, were shown to be readily ingested by larvae of the mud crab, Scylla serrata (ForsskcEl). In an effort to improve experimental MBD developed for S. serrata larvae, this study determined the effects of various binders on estimated larval ingestion of MBD as well as their leaching rates. Microbound diets with the same dietary compositions were bound with either agar, alginate, carrageenan, gelatin or zein. All diets contained p#tC-labelled rotifers and were fed to Zoea I, III, V larvae and megalopae. The p#tC content of larvae fed p#tC-labelled MBD for 2 h was used to estimate the relative ingestion rates of MBD. For all larval stages tested, the estimated mean larval ingestion of MBD did not differ significantly between binder types (P>0.05). Determination of the amount of p#tC-labelled nutrient leaching from MBD bound with various binders after 30, 60 and 240 min of immersion showed that for all types of binders, p#tC leaching occurred primarily within the first 30 min of immersion. Zein-bound MBD consistently showed the lowest numerical leaching rate among the five binders tested for all immersion periods examined, and the differences compared with other binders were often significant, particularly after 60 and 240 min of immersion. Larval feeding experiments showed that MBD prepared with binders showing higher rates of leaching were not utilized to a greater degree by S. serrata larvae. Furthermore, unnecessary leaching from MBD particles wastes dietary nutrients and is likely to impact on water quality. On this basis, our results suggest that because of its consistently lower leaching rates, zein is probably a more suitable binder for MBD developed for S. serrata larvae.