The Heteractis magnifica assemblage at the tip of the Sinai Peninsula was examined. The actinian size, location, and number of resident anemonefishes were recorded. The anemones were found at depths down to approximately 40 m and the sizes of clustering H. magnifica and clusters were positively correlated with depth. The shallow waters of the anemone assemblage contained few mainly small, solitary actinians. There seemed to be a tendency for solitary actinians to cluster once they reached a certain size-range. The resident anemonefishes Amphiprion bicinctus and Dascyllus trimaculatus were present in very large numbers (approximately 250 and 1800 respectively) and the A. bicinctus home range size was positively correlated with depth.

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Juvenile anemone¢sh Amphiprion ocellaris were tested in two behavioural laboratory set-ups for their ability to visually or chemically recognize conspeci¢cs. Individuals of two other species of anemone¢sh, A. clarkii and Dascyllus aruanus, were also used as test specimens for recognition. The results indicate that juvenile A. ocellaris recognize conspeci¢cs visually rather than by olfaction. This is contrary to their ¢nding mechanism of their host anemone. However, the results also indicate that the juvenile A. ocellaris are neither attracted nor deterred by the presence of conspeci¢cs. This is contrary to the settling mechanisms of the damsel¢sh D. aruanus and D. reticulatus, and of the temperate herring Clupea harengus. Hence the results emphasize the variation of sensory abilities and behaviours in ¢sh larvae and juveniles. It is not an area prone for generalizations.

The olfactory organs in juvenile Dascyllus aruanus and Amphiprion ocellaris, studied by scanning and transmission electron microscopy (SEM and TEM), consisted of two bilaterally radial rosettes per specimen, fan-shaped, located medio-ventrally, one in each of two olfactory chambers. In D. aruanus the rosette comprises six lamellae, three on each side of a midline raphe; in A. ocellaris 12 lamellae, six on each side. In both species, the sensory regions in the lamellae are continuous, except for the margin of the lamellae, and richly covered with stereocilia. Areas with juvenile bipolar receptor cells were observed in both species. Two dissimilar types of olfactory receptor cells in the sensory epithelium: ciliated and microvillous were observed.