New research into how fish use fins for swimming

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A new laser imaging device has given scientists a more accurate picture of the role the dorsal and anal fins play in fish swimming.

The study, conducted by Brooke Flammang and colleagues from Harvard’s Museum of Comparative Zoology and TSI Incorporated, is to be published in a forthcoming issue of the journal Biology Letters.

The authors used a volumetric velocimetry imaging system via lasers to obtain an instantaneous three-dimensional view of the wake of a swimming fish as a basis for their research.

Scientists have previously thought that the caudal fin of the fish provides the main propulsive force while swimming, with the dorsal and anal fins acting as stabilisers. However, the results of the study showed that the movements of the dorsal and anal fins contribute significantly to the caudal-fin wake, implying that these fins are not merely acting as stabilisers, but function as additional propellers.

Using four Bluegill sunfish (Lepomis macrochirus) and one Red top ice blue zebra cichlid (Maylandia –or Metriaclima – greshakei), the authors placed each fish in a flow tank that had tiny plastic particles suspended in the water.  The particles were illuminated with laser pulses and recordings made.

The results showed that the caudal fin produced wake flow patterns that closely match current models based on two-dimensional analyses in most respects, but also showed that the dorsal and anal fin produced wakes that interacted significantly with that of the caudal fin, something that had not been demonstrated in two-dimensional analyses.

For more information, see the paper: Flammang, BE, GV Lauder, DR Troolin and TE Strand (2011) Volumetric imaging of fish locomotion. Biology Letters doi:10.1098/rsbl.2011.0282

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