How Do Fish Swim

Slide 1:How Do Fish Swim?

A Presentation for The Angelfish Society by Tamar Stephens For the April 22, 2007 General Members Meeting

Slide 2:To be able to swim, fish need to:

Overcome drag Maintain their vertical position in the water column Maintain an upright position Change directions Move efficiently

Slide 3:This presentation gives an overview of the roles of:

Slime coat Body shape Swim bladder Fins Skeletal System Musculature

Slide 4:Overcoming Drag

Slide 5:Imagine wading through water�

The first thing you notice is that you have to push hard against the water to move forward. The faster you go, the harder you have to push. With each step you have to overcome drag.

Slide 6:Drag Forces

Pressure drag is the force needed to push water out of the way to swim forward. Frictional drag can cause turbulence, making it harder for water to flow smoothly across an object. An angelfish�s streamlined body shape reduces pressure drag. The slime coat provides a smooth surface that allows laminar flow and minimizes frictional drag. � � Figure from http://www.geocities.com/aquarium_fish/how_fish_swim.htm

Slide 7:Maintaining Vertical Position

Slide 8:Neutral Buoyancy

If you have raised angelfish, you have almost certainly seen little belly sliders that have to work hard to swim upward to feed. Maybe you have seen fry or small juveniles that have over-inflated swim bladders and have to work hard to swim downward to keep from floating on the surface. It takes less energy to be neutrally buoyant, so the angelfish neither bobs to the surface or sinks.

Slide 9:The Swim Bladder maintains neutral buoyancy

The swim bladder acts just like a balloon � with the ability to control the amount of gas. More gas is added to the swim bladder to move to a higher level in the water. Gas is released from the swim bladder to move to a lower position in the water.

Slide 10:Deflating the Swim Bladder

The primary gas in a swim bladder of angelfish is oxygen. To maintain a lower position, the swim bladder must release some of the oxygen. Deflating the swim bladder is a passive process. Higher pressures inside the swim bladder force oxygen to diffuse into the blood stream in surrounding capillaries. This allows the fish to sink to a lower depth. O2 O2 O2 High Pressure O2 O2

Slide 11:Inflating the Swim Bladder

Inflating the swim bladder is an active process that generally involves a gas gland. The gas gland is rich with capillaries and acts to concentrate oxygen until the pressure of oxygen in these capillaries is greater than in the swim bladder. Oxygen will then diffuse from capillaries associated with the gas gland into the swim bladder, causing it to inflate, and allowing the fish to rise.

Slide 12:Maintaining Vertical Orientation

Slide 13:Maintaining an Upright Position

If you start to lose your balance, what do you do? You stick your arms out to your sides.

Slide 14:Angelfish use their fins to maintain �balance�

I once found an angelfish in a batch of half-grown juveniles that had no pectoral fins. (I have no idea how it lost them � but the fins were completely gone, and I had never noticed any swimming problems in any of the fish in that tank before.) This fish would work its muscles very hard as if it were using its pectorals, and could often maintain a tenuous vertical position. It also used strategies such as resting between a lift tube and the side of the tank. The least little disturbance, or even the challenge of trying to eat, would send this fish tumbling wildly out of control in all directions.

Slide 15:Angelfish use fins to control pitch, roll and yaw

Figure from http://www.geocities.com/aquarium_fish/how_fish_swim.htm

Slide 16:Angelfish Fins

Pectoral Fins act as rudders and hydroplanes to control pitch and yaw. Also act as brakes. Dorsal Fin controls roll. Anal Fin controls roll. Caudal Fin provides thrust and controls direction. Ventral Fins help control pitch.

Slide 17:Efficient Motion

Slide 18:How many of you swim? After an hour of swimming, how do you feel? Tired? Could you swim all day long? Probably not � you would be exhausted long before the day was done. So how can fish swim with becoming worn out?

How do angelfish move efficiently?

Slide 19:First let�s look at how they move

The muscles provide the power for swimming and constitute up to 80% of the fish itself. Muscle blocks are arranged in multiple layers (myomeres) arrayed in several directions that allow the fish to move in different directions. Fish swim by contracting and relaxing a succession of myomeres (muscle blocks) alternately on each side of the body. The alternate shortening and relaxing of successive myomeres bends the body first toward one side and then toward the other, resulting in a series of waves traveling down the fish's body. This action starts at the head and progresses down toward the tail. The skeletal system acts as a fulcrum for the muscles.

Slide 20:Diagram showing sinusoidal wave traveling down fish�s body

Figure from http://www.geocities.com/aquarium_fish/how_fish_swim.htm

Slide 21:Now let�s look at how they move efficiently�

For us to move efficiently, we need to push against something that has greater inertia than we do. We push against the ground when we walk. Swimmers will push off from the side of the pool to get a faster start. Fish also need to push against something to move � but water by itself does not provide much inertia, because it can be easily pushed aside. So simply wriggling or flapping the tail will not give the fish very efficient forward motion.

Slide 22:Fish create vortices in the water

If you create a vortex in the water, then just as a spinning top has more energy to stay upright, the spinning water has more inertia and is harder to push aside. Fish create vortices (cause the water to spin) with the motion of their body and fins. This provides something the fish can push against to propel itself forward. Figure from http://www2.biology.ualberta.ca/jackson.hp/IWR/Content/Anatomy/Swimming/Information/index.php

Slide 23:The vortices have substantial inertia

The spin of these vortices is strong enough that they stay in place long enough for the fish to push against them. The fish�s motion is similar to sliding through a series of pegs that it pushes against. The vortices actually stay in place long enough that another nearby fish can take advantage of them. Figure from http://www2.biology.ualberta.ca/jackson.hp/IWR/Content/Anatomy/Swimming/Information/index.php

Slide 24:References

I hope you enjoyed this presentation. Here are references I used in putting this presentation together. You can get more detailed information from these sources on line. http://www.news.harvard.edu/gazette/2000/03.23/efficient.html http://www.hno.harvard.edu/gazette/2003/12.04/15-fish.html http://www.geocities.com/aquarium_fish/how_fish_swim.htm http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/swim.htm http://www.amonline.net.au/FISHES/students/dissect/swimbladder.htm http://lookd.com/fish/swimming.html http://www2.biology.ualberta.ca/jackson.hp/IWR/Content/Anatomy/Swimming/Information/index.php

Slide 25:The End