# Acceleration due to…fish?

Fish swim. Everyone knows this. What’s interesting is looking closer at how they swim and the mechanics of the forces they generate while swimming. Most people might take this for granted, but being a highly curious ichthyologist, I decided to look at the science. Instead of looking at mounds and mounds of data trying to compare apples to oranges, so to speak, I ran some calculations in order to compare apples to apples. Something I could understand. What I learned was both impressive and awesome, but first, some simple physics…

Acceleration and g-forces

Acceleration can be defined as the change in an object’s velocity over a given time frame. For example, if we are driving on the interstate at 31.3 meters per second (which is approximately 70 mph) and we accelerate to 35.8 meters per second (approximately 80 mph) in 10 seconds then our change in velocity is 4.5 m/s over a 10 second period, and our acceleration is 0.45 m/s2. Now, an object in free fall here on Earth will accelerate towards the ground at 9.8 m/s2 because of gravity. The odd thing is acceleration is an indirect cause of weight, which can be calculated by multiplying your mass by the acceleration due to gravity, 9.8 m/s2.

Acceleration also plays a role in a force we’re all familiar with – the g-force (noted as “g”). The g-force is the sensation of weight you feel when you accelerate in a fast car or on a thrilling rollercoaster ride. We’ve all felt it. So you might be wondering how it is calculated. It is calculated by dividing your acceleration by 9.8 m/s2. In simple terms, 1 g-force is the force of gravity (or your weight) while standing on Earth. 2 g’s is twice the force of gravity (or twice your weight) and so on. Ok, so what does all this have to do with fish? Well, I’m glad you asked.

Acceleration and fish

There have been several studies investigating the mechanics and intricacies of how fish swim. I sifted through the scientific literature and found several studies that measured the acceleration of a particular species for one reason or another. From these reported values I calculated the g’s each fish experiences when they accelerate. Before we look at those numbers let’s look at some common values to establish a baseline for comparison:

Usain Bolt accelerated 9.5 m/s2 out of the blocks during his world record 100 m dash. During this time he experienced 0.97 g’s.

Astronauts experience around 3 to 5 g’s during a shuttle launch.

An average person will lose consciousness somewhere around 5 g’s.

Jet fighter pilots are trained to withstand 9 g’s.

For an average person, serious injury and/or death will occur around 9 g’s.

Now for the calculations…

 Species Common name Acceleration m/s2 g – force Study Lepomis cyanellus Green sunfish 15.67 1.60 Webb 1975 Pomatomus saltatrix Bluefish 20.6 2.10 Dubois et al. 1976 Myoxocephalus scorpio Short-horned sculpin 22 2.24 Beddow et al. 1995 Cottus cognatus Slimy sculpin 22.7 2.31 Webb 1978 Perca flavescens Yellow perch 23.9 2.44 Webb 1978 Luxilus cornutus Common shiner 28.7 2.93 Webb 1978 Lepomis macrochirus Bluegill 28.8 2.94 Webb 1975 Etheostoma caeruleum Rainbow darter 32.3 3.29 Webb 1978 Oncorhynchus mykiss Rainbow trout 59.7 6.09 Harper and Blake 1990 Micropterus dolomieu Smallmouth bass 110 11.21 Webb 1983 Pterophyllum sp. Angelfish 114.7 11.69 Domenici and Blake 1993 Xenomystus nigri Knifefish 127.9 13.04 Kasapi et al. 1993 Esox lucius Northern pike 151.3 15.42 Frith and Blake 1991

It is incredible to note that Northern pike (Esox lucius; pictured above) can accelerate at 151.3 m/s2 and generate an astonishing 15.4 g’s! Let’s look at it in another way. Northern pike accelerate at 338.4 mph/s! Even the small common shiner (Luxilus cornutus; pictured below) accelerates at a rate that generates 3 times the g’s than that of Usain Bolt – the fastest human alive.

It puts things in quite the perspective, and undoubtedly demonstrates how incredible this group of vertebrates really are. Characteristics in their anatomy and physiology, such as body and muscle shape, allow them to perform at insane levels, but that is for another post.

–  Chris

References and photo credits

Webb, P.W. 1975. Acceleration performance of rainbow trout Salmo garidneri and green sunfish Lepomis cyanellus. Journal of Experimental Biology 63:451-465.

Dubois, A.B., Cavagna, G.A. and Fox, R.S. 1976. Locomotion of bluefish. Journal of Experimental Zoology 195:223-226.

Beddow, T.A., Van Leeuwen, J.L. and Johnston, I.A. 1995. Swimming kinematics of fast starts are altered by temperature acclimation in the marine fish Myoxocephalus scorpius. Journal of Experimental Biology 198:203-208.

Webb, P.W. 1978. Fast start performance and body form in seven species of teleost. Journal of Experimental Biology 74:211-226.

Harper, D.G. and Blake, R.W. 1990. Fast-start performance of rainbow trout Salmo gairdneri and northern pike Esox lucius. Journal of Experimental Biology 150:321-342.

Webb, P.E. 1983. Speed, acceleration and maneuverability of two teleost fishes. Journal of Experimental Biology 102:115-122.

Domenici, P. and Blake, R.W. 1993. The effect of size on the kinematics and performance of angelfish (Pterophyllum eimekei) escape responses. Canadian Journal of Zoology 71:2319-2326.

Kasapi, M. A., Domenici, P., Blake, R. W. and Harper, D. G. 1993. The kinematics and performance of the escape response in the knifefish Xenomystus nigri. Canadian Journal of Zoology 71:189-195.

Frith, H. R. and Blake, R. W. 1991. Mechanics of the startle response in the northern pike, Esox Lucius. Canadian Journal of Zoology 69:2831-2839.