32 PHOSPHORUS TRANSFER IN SYSTEMS OF FISH AND AMPHIPODS EXPLOITING DETRITUS PARTICLES

Detrital size preferences of the fish Mugil sp. and the amphipod Echinogammarus veneris were determined in the laboratory by P-32. Three different size-classes of leaf-detritus particles, inoculated with a fungus, were offered separately in 24-h experiments. Detritus P-32 increased with particle size, depending on the growth of microflora. Both species preferred the largest size-class. In mixed-species experiments, P-32 uptake by Mugil was significantly less than when it was alone. A similar P-32 transfer was measured in Mugil fed on the largest particles, previously utilized by E. veneris. This indicates that the feeding activity of the amphipod indirectly affects the detrital utilization by Mugil sp. It is suggested that the influence might depend on the microbial impoverishment and the change in the particle size.