Leaping blenny: A fish out of water

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The Pacific Leaping blenny (Alticus arnoldorum) has evolved a rich and complex social life out of the water, according to a study by researchers from Australia and the USA to be published in a forthcoming issue of the journal Ethology.

Terry Ord and Tonia Hsieh carried out their study on Guam, where the Leaping blenny is reasonably abundant on its shores. They first carried out an abundance survey at two locations on the island, before conducting detailed behavioural observations on individual adult males and females.

The authors found that the blennies confined their activity to the day and were most active during mid-tide and when the temperatures were neither too high nor too low (27–30°C). This meant that the blennies were at their most active for only two to four hours per day.

At high tide, the waves were often so violent that the blennies spent most of their time clinging to rocks or sheltering in crevices and holes above the waterline. At low tide or at high temperatures, the blennies were observed to retreat into moist crevices and rock holes to avoid drying out.

Observations by the authors also suggest that the males defend small territories centred on rock holes. Males were observed to vigorously nod their heads at the entrance of their holes in order to attract passing females to enter and spawn with them (see the short video below).

Although females were not territorial and spent most of their time grazing on algae, they were aggressive to conspecifics, especially those that encroached their feeding sites.

The blennies appeared to have adapted so well to living out of the water that they appeared not to voluntarily return to the water and spent almost all of their time avoiding submersion by the waves. Rather than jump into the water, the typical escape response of the blenny to a perceived threat was to hop rapidly along the rocks and hide in crevices above the waterline.

Because the Leaping blenny is behaviourally terrestrial while continuing to be constrained by its dependence on water for respiration, it offers a unique opportunity to discover how the transition from water to land may have taken place in the ancestors of all tetrapods, according to the authors.

For more information, see the paper: Ord, TJ and STT Hsieh (2011), A highly social, land-dwelling fish defends territories in a constantly fluctuating environment. Ethology doi: 10.1111/j.1439-0310.2011.01949.x

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