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The effect of hypoxia on the anti-predator response of grey mullets

SUMMARY Result No. 1: The effect of hypoxia on the anti-predator response of grey mullets.

Escape performance was investigated in the golden grey mullet Liza aurata exposed to various levels of oxygen: >85 (i.e. normoxia), 50, 20 and 10 % air saturation. Since the golden grey mullet performed aquatic surface respiration when air saturation approached 15-10 %, escape performance was tested at 10 % air saturation with and without access to the surface (10 % S and 10 % C, respectively). Various locomotor and behavioural variables were measured, such as cumulative distance, maximum swimming speed, acceleration, responsiveness (per cent of responding fish), response latency and directionality. Golden grey mullet showed a decrease in responsiveness when the oxygen level was reduced to 10 % air saturation, whether the surface access was obstructed or not. Hypoxia did not have any effect on the response latency.

Cumulative distance and maximum swimming speed over a fixed time were significantly different between normoxic conditions and 10 % C, while no differences were found in maximum acceleration.

While the fish escaped away from the stimulus in normoxia, the proportion of away and towards responses was random when the oxygen was <20 % air saturation. This suggested an impairment of the left-right discrimination at the initiation of the response. Hypoxia affected golden grey mullet escape performance mainly through an impairment of responsiveness and directionality, while locomotor performance was affected only in severe hypoxia when the surface was obstructed. The study showed that, in addition to forcing the fish to the surface as shown by previous studies, hypoxia may also increase the vulnerability of grey mullets facing a predator by directly impairing its escape performance.

Reported by

International Marine Centre
Località Sa Mardini
09072 Torregrande
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