It is widely believed that because of biomechanical trade‐offs, fish body shape and the mode of propulsion are strong predictors of swimming performance, with the best cruisers, maneuverers and accelerators having different body forms and emphasizing different propulsion mechanisms. This paradigm is regularly projected onto routine swimming behaviour and dominates the ecomorphological literature, despite the paucity of field measurements.
In this study, we measured variation in swimming behaviour among 48 species of Indian Ocean coral reef fishes using recordings from a remote stereo video system. We measured average swimming speed, average swimming bout distance, frequency of turns and percent of time spent station‐holding and looked for the predicted trade‐offs between them.
We find little evidence of the expected relationships between swimming behaviours across species, little evidence that body shape affects swimming and few differences between species that swim by undulating the body and those that emphasize the use of median and paired fins. Taxa widely thought of as archetypical maneuverers (Chaetodon) and cruisers (Caranx) were not outliers in any behaviours.
Our results indicate that swimming behaviour is not easily predicted from simple measures of body shape and that alternative swimming modes can produce comparable behavioural profiles.
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To test life‐history theory that body size and sex should influence how animals allocate time to foraging versus reproductive activities, we measured the effects of size and sex on courting success and foraging behaviour of black surfperch Embiotoca jacksoni off Santa Catalina Island, southern California. Observations of focal fish were made while snorkelling, during which the length of each fish (estimated to the nearest cm), total duration of courting encounters and foraging rates were recorded. We made observations during and outside the mating season. Courtship occurred only between pairs and its duration increased with the size of both the male and female. Although males would court females that were smaller or larger than themselves, pairs that were closely matched in size had long courting sessions, whereas those that differed considerably in size courted only briefly. Small fish foraged more than larger fish, both during and outside the mating season. Males and females foraged at similar rates outside of the mating season, but during the mating season males reduced their foraging rates to less than half that seen outside of the mating season, whereas females continued to forage at the same rate. This decrease in foraging rate of males during the mating season was seen in all sizes of males but was proportionally greatest in the largest males. These observations indicate that males trade off time spent on foraging for time spent courting during the mating season, whereas females do not.
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