To be able to swim, fish need to: Overcome drag Maintain their vertical position in the water column Maintain an upright position Change directions Mo

Transcription

1 How Do Fish Swim? A Presentation for The Angelfish Society by Tamar Stephens For the April 22, 2007 General Members Meeting 1

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 2

3 This presentation gives an overview of the roles of: Slime coat Body shape Swim bladder Fins Skeletal System Musculature 3

4 Overcoming Drag 4

5 Imagine wading through water The first thing gy 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. 5

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 6

7 Maintaining Vertical Position 7

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. 8

9 The Swim Bladder maintains neutral lb 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. 9

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. O 2 O 2 O 2 High O 2 Pressure O 2 This allows the fish to sink to a lower depth. 10

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 i 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. 11

12 Maintaining Vertical Orientation 12

13 Maintaining an Upright Position If you start to lose your balance, what do you do? You stick your arms out to your sides. 13

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. 14

15 Angelfish use fins to control pitch, roll and yaw Figure from 15

16 Angelfish Fins Dorsal Fin controls roll. Pectoral Fins act as rudders and hydroplanes to control pitch and yaw. Also act as brakes. Ventral Fins help control pitch. Anal Fin controls roll. Caudal Fin provides thrust and controls direction. 16

17 Efficient Motion 17

18 How do angelfish move efficiently? 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 without becoming worn out? 18

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 es of waves traveling down the fish's s body. This action starts at the head and progresses down toward the tail. The skeletal system acts as a fulcrum for the muscles. 19

20 Diagram showing sinusoidal wave traveling down fish s body Figure from quarium _ fish/how_ fish_ sw im.htm 20

21 Now let s look at how they move efficiently i 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. 21

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 i water has more inertia i 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 Swimming/Information/index.php 22

23 The vortices have substantial inertia i 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 s motionis is similar to sliding through a series of pegs that it pushes against. The vortices actually stay in place long enough that t another nearby fish can take advantage of them. Figure from Swimming/Information/index.php 23

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 htm htm hp/iwr/content/anatomy/ Swimming/Information/index.php 24

25 The End 25