1. Lecture 12 Buoyancy, muscle blocks, labriform swimming Readings: Shoele K. & Zhu Q. 2010. Numerical simulation of a pectoral fin during labriform swimming. J.Exp. Biology 213: 2038-2047. (Intro) Sfakiotakis: Review of Fish Swimming Modes…

2. Density is mass per unit volume; so regulating your density is a matter of losing weight or increasing your volume. Some swimming animals regulate body density. You soon realize as a scuba diver that swimming is much easier when you are not working to stay down or to keep from sinking, when you are neutrally buoyant. A diver achieves neutral buoyancy by regulating body density with a buoyancy compensator (BC). Bony fishes do the same thing. Buoyancy

3. Buoyancy see Vogel Comparative Biomechanics p. 96 Archimedes’ Law : objects heavier than the volume of water they displace will sink; objects lighter than the volume of water they displace will rise. A fish is buoyed up by a force equal to the weight of the water it displaces. It can change this force by changing its volume, i.e., displacing more or less water. Secreting oxygen gas into its swim bladder from the blood, the fish increases its volume and displaces more water, so increasing the force acting to make it rise in the water column. Conversely it can absorb oxygen gas from the bladder and so sink. Inland fishes of NY, Cornell

4. Swim bladder /Gas bladder Many bony fishes have a single median gas bag in their body used to change their density, giving neutral buoyancy at different levels in the water column. This bladder, situated just below the backbone and just above the viscera, contains oxygen at a high concentration; the oxygen is actively secreted from the blood. Fisheries & Oceans Canada Ancestors of bony fishes, living in fresh water, evolved lungs to supplement their gills in times of drought. When some of these ancestors reinvaded the seas these lungs evolved into swim bladders.

5. How to eat a fish A knowledgeable person who has some idea of myotomes and axial skeletons also probably knows how to eat a fish. When its cooked properly your first step can be to extract the entire intact bony axial skeleton if you’re careful. Axial skeleton vertebrae and ribs are no problem, they all connect. But there are still the Y-bones as a lurking throat-clogging danger -- because they’re not attached to the rest of the skeleton. You might also not be surprised that different fish species have different skeletal structure; this goes with expecting the diversity that is typical of animals. Freeimageslive

6. Ray-finned fishes: lepidotrichia or ‘fin rays’ support the fin and allow for variable surface area in deployment Butterfly fish skeleton (Wikki) Ribs connect to the backbone giving the axial skeleton What is the function of y bones?

7. White muscle and anerobic ‘predation function’ Rate of oxygen supply to a muscle can be the limiting factor in its activity. During critical moments of predation (either capture or escape) the normally supplied oxygen via lungs and bloodstream can be inadequate. Bony fishes have a separate set of ANEROBIC WHITE muscles (pink in salmon). These muscles convert glucose to lactic acid to get their energy for contraction. The energy obtained in this way comes via a less efficient metabolic process and the accumulation of lactic acid is also a negative effect. But for short periods a fish can make a highly adaptive ‘burst of speed’.

8. Text for this slide and next are taken from: Environmental Science Investigation, an organization concerned about declining salmon stocks in the Fraser River >esi.Stanford.edu< Bodybuilding estore Most of the [muscle blocks] in a fish … [are] white muscles. In most salmon species these myotomes are pink due to a pigment salmon get from their diet. So not really ‘white’ and not really ‘red’. RED MUSCLE WHITE MUSCLE

9. The red muscle is often a band along the side of the fish. The red muscle contains a lot of myoglobin, capillaries and also a lot of glycogen and lipids. The red muscle mass is somewhere between 0.5 to 30% of the total muscle mass in a fish, depending on the species. Active fish, such as bluefin tuna, have a higher proportion compared to sedentary species, like catfish. The red muscles are aerobic while the white muscle is mostly anaerobic. As long as a fish swims within the sustained swimming speed only the red muscles are used, while in prolonged swimming at high swim speeds, some of the white muscles are used, and this is what eventually leads to fatigue. During burst swimming the white muscles are used at maximum capacity, and this leads to a rapid fatigue. >esi.Stanford.edu< Red muscles are aerobic- sustained swimming

10. Adaptive fibre orientation in white muscle fibres in teleost fishes, taken from p. 210- 211, R. McNeill Alexander, 'Exploring Biomechanics', Mc Neill’[s figure redrawn (gkm). Why are the axial muscles of fish so strangely shaped? They look like zig-zag ‘W’s. Univ. of Michigan Museum of Zoology, UMMZ

11. HOW ARE THE MUSCLE FIBRES ALLIGNED? “…the commonest pattern has white fibers running at angles of up to 35 ̊to the long axis of the body. The [muscles are] partitioned into segments called myotomes and each fiber runs only the length of a myotome, from one partition (septum) to the next. But if you follow a series of fibers, connected end to end through the partitions [from one myotome to the next] you will find a pattern: these chains of fibers run helically, like the strands of a rope." In other words these muscle fibres describe helices and lie at changing distances from the vertebral column. Zig-zag blocks of muscle myotomes separated by myocommas

12. "Imagine that the fibers were not so arranged, but instead all ran parallel to the long axis of the body. Imagine the fish bending to such an extent [in producing body waves] that the outermost fibers of the bend, just under the skin, had to shorten by 10 %. Fibers halfway between this peripheral position and the backbone would have to shorten by only 5% and fibers right alongside the vertebrae would have to shorten hardly at all. In each tail beat, the outermost fibers would have to shorten quite a lot and relatively fast, whereas the innermost fibers would shorten much less in the same time and therefore more slowly.“ This would be very inefficient. You’re not getting good force production out of all your muscle.

13. "Now consider how the actual arrangement of white fibers affects the shortening of the muscles.“ Helical sequences of fibres run across muscle blocks like the strands of a rope (represented as red ribbons in the illustration). Each ‘fibre-chain’ lies close to the backbone for part of its course and nearer the skin of the fish's side for others. The result is that when the fish bends, say to the right, all the white fibers on the right side have to shorten by about the same percentage of their length.“ Easy to say: a little hard to visualize.

14. The axial muscles on the left of the vertebral column are antagonized by those on the right and vice versa. These left or right side 'chains' of fibres (running across a series of 'zig-zag' myotomes) will all contract and shorten in phase with each other, reaching the same % shortening all at the same time and relaxing maximally at the same time. In other words they go through their cycle of contracting and relaxing together. But they are located at different points between the skin and the backbone as they follow their helical pattern. Thus at the time these 'functional myotome series' contract simultaneously they are at different phases of the body wave; if they were not at different phases they could not shorten by a uniform per cent.

15. Quick mention of amphioxus and its notochord, precursor to the vertebrate backbone IASZoology.com Myotomes of longitudinally aligned muscle fibres separated by septa and with chevron shape, perhaps for the same reasons as fish myotomes are W- shaped: obtaining simultaneous shortening relative to phase of a body wave and distance from the notochord. The notochord makes antagonists of the muscle blocks of the right and left sides.

16. See Sfakiotakis: Review of Fish Swimming Modes… Fish jump, burrow, fly, glide, jet -- but most use either BCF or MPF. BCF propulsion: retrograde waves using BODY CAUDAL FINS. MPF oscillation: MEDIAN PECTORAL FINS.

18. Creole Wrasse, my (Dr. Morris) favourite Caribbean reef fish, yellow-marked males with females in schools; odd swimming habit attracted my attention. Corey Fscher Bonaire

19. “15-20% of living fishes use their pectoral fins as their primary mode of locomotion” (Thorsen & Westneat 2004); relatively slow swimmers creating thrust with pectorals. Ask yourself ‘why evolve toward pectoral fin locomotion and away from BCF? BCF associated with higher speeds. “cichlids, damselfishes, parrotfishes, wrasses [above pictures of the creole wrasse, Clepticus parrae, Bonaire], surfperches, many of angelfishes, butterfly fishes, goatfishes, surgeonfishes and other coral reef families” emphasize pectorals Labriidae is the family name of wrasses: and their family name is the basis of the term labriform as a swimming mode.

20. Labriform swimming is a mode of fish swimming in which propulsion is achieved by cyclic movement of just the pectoral fins; the body is kept straight like a projectile, while the pectorals are oscillated up and down, abducted (away from body) and adducted (toward the body) complexly. Pectoral propulsion occurs in a combination of rowing and flapping that varies with speed (Sfakiotakis et al. 1999). Rowing is ‘drag-based labriform mode’; flapping is ‘lift-based labriform mode’. Labriform-swimming fish rarely exhibit a clearly rowing or flapping movement (lift-based vs drag-based): they use a complex combination of them that varies with speed. I think these movement models are not exactly adhered to, but they help to explain the range of movement. The fins also change shape: “the pectoral fins of the sea perch pass a wave back over their length as a result of phase lags in the movement of the individual fin rays” (Sfakiotakis 1999) An MPF swimming fish using primarily its pectoral fins: is the creole wrasse. Labriidae hence ‘labriform’ swimming.

21. See Sfakiotakis et al. 1999, p. 248 Two main oscillatory types when swimming with the pectoral fins: Drag-based, Lift-based. Thie first is a ‘rowing’ action the latter ‘flapping’ “similar to that of bird wings”. Figs from Sfakiotakis 1999 1 2 Drag based swimming is more efficient than lift based at slow speeds (Vogel 1994). Vogel, S. 1994. Life in Moving Fluids. Princeton Univ. Press, Princeton, N.J.

22. Drag-based labriform swimming There are two phases: power stroke and recovery stroke. In the power stroke the fins move “posteriorly perpendicular to the body at a high attack angle and with a velocity greater than the overall swimming speed. On the recovery the fins are “feathered to reduce resistance and brought forward”. “ Thrust is generated due to the drag [on the fin] encountered as the fin is moved posteriorly.” Feathered: turned edge on

23. Lift-based labriform pectoral fin swimming Lift forces are generated in the plane perpendicular to the direction of fin motion; with lift-based labriform pectoral fin swimming this can occur during both the upstroke and the downstroke. No recovery stroke is necessary. Lift-based fins can generate larger, more continuous and more efficient thrust than fins performing rowing motions.