Transcript Lecture 12

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…
Buoyancy
• 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 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
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.
• 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.
How to eat a fish
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
Butterfly fish skeleton (Wikki)
What is the function of y bones?
Ray-finned fishes:
Ribs connect to the backbone giving the axial skeleton
lepidotrichia or ‘fin rays’
support the fin and allow for variable surface area in deployment
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’.
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<
RED MUSCLE
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’.
WHITE MUSCLE
Bodybuilding estore
Red muscles are aerobic- sustained
swimming
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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<
Why are the axial muscles of fish so strangely shaped? They look like zig-zag ‘W’s.
Univ. of Michigan Museum of Zoology, UMMZ
Adaptive fibre orientation in white muscle fibres in teleost fishes, taken from p. 210211, R. McNeill Alexander, 'Exploring Biomechanics', Mc Neill’[s figure redrawn (gkm).
• 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
• "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.
• "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.
• 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.
Myotomes of longitudinally aligned
muscle fibres separated by septa and
with chevron shape, perhaps for the
same reasons as fish myotomes are Wshaped: 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.
IASZoology.com
Quick mention of amphioxus and its notochord,
precursor to the vertebrate backbone
• 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.
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
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“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.
An MPF swimming fish using primarily its
pectoral fins: is the creole wrasse.
Labriidae hence ‘labriform’ swimming.
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)
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” .
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.
1
2
Figs from Sfakiotakis 1999
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
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.