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Homing behaviour of an inter-tidal fish Oligocottus maculosus girard Khoo, Hong Woo

Abstract

The purpose of the study is to find out how Oligocottus maculosus homes and what mechanisms or sensory channels are involved in the homing process. The species' home range was defined from pool fidelity and movement observations. Evidence was obtained to show that the fish homes when displaced to unfamiliar areas. The roles of season, distance and direction of displacement as well as sex, size and experience of the fish in homing were assessed. The roles of both vision and olfaction and the related environmental cues were also investigated. Some fish showed strict fidelity to specific tide-pools while others moved from one pool to another but limited themselves to a restricted group of neighbouring pools. The range of movement seldom exceeded an area of about one hundred square feet which was defined as the maximum home range. Homing, i.e. striving to return to its home range instead of going to other equally habitable areas, was observed throughout the year; homing was most successful between March and August. This seasonal variation was probably the result of mortality owing to the seasonal sea conditions. In my study O. maculosus had been shown to home from as far as one thousand feet. A decrease in homing returns with increasing distances from home was observed. This was attributed to the effects of wave action which decreased the chances of survival with increasing distances from home. Direction of displacement did not seem to affect homing performance and no difference in homing performance was observed between the sexes or among fish of different sizes. Fish which were shown to home at least once seemed to home better than naive fish though no further improvement in homing was observed when the former were repeatedly displaced. There is a strong indication that there is inherent variability in homing ability, that some fish home better than others and that learning per se is not important. Displacement experiments conducted with blind and anosmic fish had shown that blind fish could home better than anosmic fish indicating that olfaction, not vision, is more important in homing. Studies on the ability to home on cloudy nights, the ability to discriminate sea water from different sources in the laboratory and the ability to return to pools with the immediate environment destroyed further indicated the importance of olfaction in the homing mechanism of O. maculosus. How the fish finds its way from the release point to its home range is still not known with certainty. However, it is suggested that the fish homed by (i) following odour streams originating from its home area or (ii) an exploratory search process or (iii) a combination of the two processes.

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