Fish in the oceans are really fascinating! When I went scuba diving with my friends last year, I was totally intrigued by what I saw in the video clip below and got my dive master, Halbert, to film it to share with my friends who do not scuba dive.
Watch: Fish met current
Are all fish born with the natural ability to, know how not to swim against currents so that they do not waste their energy; instead remaining stationary until the currents weakens or change course before they start swimming into the direction they planned? These are however just my wild guesses.
Fish are naturally born with a wide range of responses to relative motions. The fluid properties of air and water enable fishes to orientate to flows in the water and this behaviour in water is termed rheotaxis and responses are termed rheotropism. Fish detect currents directly by flow over the body surface or indirectly by other stimuli. Indirect responses are more common and occur in response to visual, tactile and inertial stimuli resulting from displacement of the fish by the current. Reactions to displacement of visual images are called optomotor reactions.
Some of the reasons why and how fishes react to flows in water:
1) Fish show a number of hydrodynamic adaptations to life in currents. Morphological modifications are greatest in fish from torrential streams i.e. fresh water bodies. This show extreme dorsoventral (which means the axis that passes through the back of the body and the abdomen) flattening and have specialized adhesive organs. Unfortunately only in some fishes such as Dasyatidae i.e Rays in the picture below, to maneuver comfortably in currents. Other fish, however select areas of low velocity to continue swimming or decrease their buoyancy to try to find courses in the water where currents may not be so strong.
(Photo from Ichthyology- Florida Museum of natural History)
2) In the case of ‘average looking’ fish, report of an experiment done by James Liao of Harvard University and his colleagues. Fish slalom in between the vortices ie. against currents is fish were actually slaloming in between the vortices rather than intercepting the centers of each one which they do they are swimming through waters
The slaloming fish have to move side-to-side quite a bit in order to move forward just a little, but by doing so they can remain stationary, or “hold station,” against the moving current. Fish only need to contract their body muscles near the head to change position among the eddies. They don’t use all their body muscles to propel themselves forwards, as they would in smooth currents. Fsh probably hold station when they encounter turbulence and then resume normal swimming once they are out of the rough patch. Clever fishes, really.
‘Rheotropism in Fishes’, by G. P. ARNOLD. Fisheries Laboratory, Lowestoft, Suffolk URL: http://www3.interscience.wiley.com/journal/120071456/abstract (accessed on 8 April 2010)
‘Fish met current’ by Halbert Lim. URL:http://www.youtube.com/watch?v=Pb4X7v26c7I (accessed on 8 April 2010)
‘The tao of fish swimming’, by Kathleen Wren. 2010 American Association for the Advancement of Science, URL: http://www.msnbc.msn.com/id/3607002/ (accessed on 8 April 2010)