Digging with ‘hands’: observations of food capture in the flying gurnard Dactylopterus volitans (Linnaeus, 1758)

ABSTRACT

Videofilms of a foraging flying gurnard (Dactylopterus volitans) were collected at Itaipu, Niterói, RJ, Brazil. Analysis revealed details of the use of anterior parts of the pectoral fins which act as digging ‘hands’ to access infaunal prey items that are subsequently captured by oral suction feeding. Each pectoral fin has two distinct sections articulated separately on the pectoral girdle. The digging ‘anterior pectoral fin’ mainly consists of segmented and flexible fin rays but has an anterior robust unsegmented ray that provides an edge to the ‘hand’, allowing penetration of the substratum. The huge ‘posterior pectoral fins’ are supported by unsegmented rays. Most digging episodes involved one ‘hand’ and consisted of 1–7 cycles of movement with frequencies 1.15–3.74 cycles s⁻¹. During a cycle, the ‘hand’ is moved forwards and medially above the substratum, then is twisted medially and simultaneously depressed so that the anterior unsegmented ray impacts and enters the substratum. The hand is then drawn backwards and laterally to disturb the substratum. To prevent upward pitching of the head during digging, the ‘posterior pectoral fins’ are both moved anteriorly and laterally to shift the centre of gravity forwards while the caudal and second dorsal fins continue to provide propulsive force.

KEYWORDS:

• Digging for prey
• pectoral fin ‘hands’
• Syngnathiformes
• Dactylopteridae
• flying gurnards

Acknowledgements

Both authors thank Mr Oliver Crimmen (Senior Fish Curator) of the Natural History Museum, London, UK for facilitating access to a preserved flying gurnard specimen and for fruitful discussion. The second author wishes to thank Prof. Cassiano Monteiro-Neto for his invitation to visit the Marine Biology Department of the Universidade Federal Fluminense, Niterói, Brazil, under a visiting fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq. This study received Portuguese national funds through FCT-Foundation for Science and Technology-project UID/Multi/04326/2013.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Portuguese national funds through FCT-Foundation for Science and Technology [project UID/Multi/04326/2013].