The food and feeding ecology of Mugilidae in the St. Lucia lake system

The diet and feeding interrelationships of ten species of Mugilidae were studied over a two-year period in the St. Lucia lake system of South Africa. Qualitative stomach analyses were performed on over 1000 fish of more than 5 cm (standard length). All are soft bottom substrate feeders ingesting inorganic particles mixed with food items. The food of most species is the same and consists of Assiminea bifasciata , foraminifera, the large centric diatom Aptinoptychus splendens , small centric and pennate diatoms, and filamentous algae. Individual species of mullet however, differ, in the size of inorganic particles ingested and exhibit marked sand grain size preferences. The consumption of the various food items may depend upon their occurrence on substrates of the preferred particle size. There is no apparent change in diet and particle size preference according to age in any of the species and no seasonal variation was recorded in the diet. It is suggested that interspecific competition for food is reduced by substrate particle size selection and perhaps by differences in feeding periodicity. Where there is an apparent overlap in diet, as in the case of Assiminea bifasciata , on substrates of the same size then there is a superabundance of the food organism which serves to minimize competitive interactions.