OPERCULAR JETTING DURING FAST-STARTS BY FLATFISHES

Citation
El. Brainerd et al., OPERCULAR JETTING DURING FAST-STARTS BY FLATFISHES, Journal of Experimental Biology, 200(8), 1997, pp. 1179-1188
Citations number
27
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biology
ISSN journal
0022-0949
Volume
200
Issue
8
Year of publication
1997
Pages
1179 - 1188
Database
ISI
SICI code
0022-0949(1997)200:8<1179:OJDFBF>2.0.ZU;2-2
Abstract
When attacked by predators, flatfishes perform fast-starts that result in a rapid take-off from the ocean bottom on which they lie. High-spe ed video recordings of the blind side of flatfishes indicate that they expel a coherent jet of water from the blind-side opercular valve dur ing take-off. Buccal pressure recordings in winter flounder (Pseudople uronectes americanus) show that a buccal pressure pulse begins 0-20 ms before the beginning of the fast-start and has a range of mean magnit udes for three individuals of 1.6-10.7 kPa. We hypothesize that one fu nction of the opercular jet in flatfishes may be to reduce the effects of Stefan adhesion. Stefan adhesion occurs as the fish lifts its head up rapidly from the ocean bottom, when water must flow into the space forming beneath the fish. Water viscosity opposes this rapid shear, a nd a suction pressure develops under the fish, making it more difficul t for the fish to escape from the bottom. To estimate the magnitude of Stefan adhesion, we simulated fast-starts using a physical model in w hich a dead flounder was pulled upwards with an acceleration of 95 m s (-2). Results from the physical model indicate that up to 35% of the t otal force required to lift the head at 20 ms into the start can be at tributed to Stefan adhesion. Despite this large adhesion force, previo us work has shown that live flatfish do not show improved fast-start p erformance when Stefan adhesion has been eliminated by starting the fi sh from an open wire grid. Thus, live fishes are likely to be using be havioral mechanisms to reduce the adhesion force. Both the timing and location along the body of the opercular jet indicate that it is ideal ly suited to attenuate the effects of Stefan adhesion. Propping the bo dy up on the median fins may also reduce adhesion by increasing the in itial distance between the fish and the ocean floor.