By tracer experiments using 32P and a comparison of sediment and stomach content particle sizes, Mugil cephalus Linnaeus is shown to prefer very fine particles wherever sediments are involved in feeding. It is suggested that these small inorganic and plant detrital sediment particles are much richer both in absorbed organic material and in adsorbed bacteria, Protozoa, and other microorganisms than the coarser material that the mullet rejects. This selectivity results in substantially higher organic values of the stomach contents than of the sediments.