Thursday, April 25, 2013

Tunas with Laser Beams!

A yellowfin tuna swims in the flume as an infrared laser beam reveals the flow patterns around its tail (photo B. Block)

A collaborative project between Massachusetts Institute of Technology and the TRCC team has been undertaken to characterize the water flow around live, swimming tunas.  Professor Block and visiting MIT Professor Alexandra Techet and graduate student Leah Mendelson have been leading the charge on this complex and challenging study.  The team is on a mission to better understand the underlying mechanisms that enable these highly streamlined organisms to swim at high speed and migrate across ocean basins.

MIT graduate student Leah Mendelson dawns her laser safety glasses as she captures high speed footage of the swimming tuna (photo B. Block)

Over the past 6 months Postdocs Adrian Gleiss and Jon Dale and graduate student Dane Klinger have trained bluefin and yellowfin tuna to swim steadily in the lab’s respirometer.  This specialized tank generates flow that enables the tuna to swim in place in a sealed acrylic chamber.  The tunas become acclimated to swimming in the environment through subsequent runs in the respirometer, and for this week’s project we’ve selected the calmest, most steady-swimming individuals as brave test pilots for this never-before-attempted study.

High-speed footage of the illuminated particles, seen here flowing over a bluefin tuna’s finlets, will be input into a mathematical model that will reconstruct the fluid motion around these features (video B. Block)

The team is applying a technique called PIV (Particle Imaging Velocimetry) to observe the fluid flow around the body and fins of a swimming tuna.  This technique involves seeding the seawater in the respirometer with small (20 micron) polyamide particles, which when illuminated by an infrared laser beam enable a high-speed camera to track the motion of each individual particle.  Subsequent analysis of this high-speed footage will enable the researchers to construct mathematical models of the particle movement around various features of the fish.  For the first time, we will be able to visualize the fluid flow from the head to tail of a swimming tuna.  Stay tuned to check out the results of this cutting edge project.  

(left-to-right) Graduate student Leah Mendelson, Professor Alexandra Techet, and Professor Barbara Block in front of the TRCC at Hopkins Marine Station (photo E. Estess)