A study into the locomotion
|Fish species are present in many varying forms all over the
world. The main difference between shapes of individual species would firstly
concern the need for them to travel through a fluid with varying densities
pressures and drags. With a combination of these problems and in turn making
best use of there form inside their chosen environment each species has
developed, sometimes radically, different body profiles.
Figure 1: Comparisons of flow around objects in viscous fluids.
: Hosford (1997), p.16
||Species such as the rainbow trout (Oncorhyncus mykiss)
have developed torpedo shaped bodies to counteract the drag confronted
in a viscous fluid. Figure 1 shows the difference in streamline effects
on two very different shaped objects in a fluid. The ideal situation
to experience in a viscous fluid would involve laminar flow, this
being smooth and thin with a creation of minimal drag. The circular
shape in figure 1 is less streamlined in appearance and at the rear
end turbulent flow is created. This is usually in the form of an eddy
or wake and consists of a thicker layer, which increases the drag.
For many fast swimming species the creation of a turbulent flow would
result in the inefficient use of resources with respect to energy
requirements. This may seem fairly straight forward but Blake (1983),
suggests although the maintaining of a laminar boundary layer is a
drag reduction system it happens to be less stable than a turbulent
flow as it creates larger pressures upon separation. As this is the
case the inducing of a turbulent boundary layer can also reduce drag.
It has been suggested that some species such as the mackerel (with
the use of added dorsal fins), and the rainbow trout (with the use
of an adipose fin) tend to induce a change in boundaries.
|Figure 2 shows that many years of development in aerofoil
technology have created a design identical to the shape of a rainbow
trout. The solid line is the aerofoil where as the dotted line is
the trout. This concludes that the rainbow trout has formed into a
highly streamlined structure.
Figure 2: Comparison of a trout body form and a typical aerofoil.
Source: Blake (1983), p.61
|The position of the shoulder will determine the type of flow over the
body of the species. The shoulder of the trout is somewhat further back
than the likes of the common bream (Abramis brama). This seems to
verify that the form compares to the habitat and lifestyle of the species.
The final point on the subject of drag would involve the use of the mucus
covering the skin of the fish. The use of mucus in filling irregularities
on the body could improve the flow characteristics of the boundary layers.
|In normal observations fish swimming can be split into steady
speeds, where the fish moves in one direction at a constant velocity or
more commonly un-steady swimming which is the continuous changing of speeds
and directions (Hoar & Randell 1978). The critical speed of a species
can only be measured from steady swimming but it is important to note that
three other phrases, prolonged, burst and sustained swimming will take place
in either of the firstly mentioned descriptions. It must be mentioned that
potential growth response is effected by the cost of locomotion, which in
tern contributes to the overall metabolic load (Ware, 1975), therefore efficient
energy use is essential. Evidence has been found that juvenile fish do feed
by moving at the appropriate speed to maximise their production rate (Ware,
Figure 3: Fatigue curves Source
: Blake(1983), p.38
Figure 4: Body propulsion of subcarangifom mode. Source
Hoar & Randell(1978), p.10
||Figure 3 shows the fatigue curve of a rainbow trout
(formally Salmo gairdneri). It clearly defines the three states
of swimming used by all species of fish. Sustained swimming includes
routine activities such as schooling and cruising and can be maintained
in excess of 200 minutes. Prolonged swimming can continue between
200 minutes to 15 seconds and entails cruising with short bouts of
vigorous movement. Burst swimming is the most inefficient form of
activity with respect to energy use and can only be achieved for short
periods of up to 15 seconds (Wilson & eggington, 1994).
The rainbow trout can be classified into the group of subcarangiform
fishes. This defines the type of body movement the species experiences
when swimming. Most fish species swim with lateral body undulations
running from head to tail. These waves run more slowly than the
waves of muscle activation causing them, reflecting the effect of
the interaction between the fish's body and reactive forces from
the water (Wardle et al.1995). The undulations of the side
to side movement in the body are slight in the anterior but there
is a significant increase in the rear half to third of the body.
The snout of the fish does not travel in a straight line but tends
to oscillate at small amplitudes along the mean path of the fish
(Hoar & Randell 1978). Figure 4 illustrates this type of movement
and clearly shows that no part of the body travels in a straight
line, but tends to follow a curving path through the water
Only at speeds of under 1 to 2 body lengths per second does the
amplitude of the body undulations change, usually there is no change
with swimming speeds. The frequency that the tail beats and the
velocity at which waves are passed to the rear of the fish directly
effect the speed of the fish. Speeds of up to 25 body lengths per
second have been recorded for fish below 0.1 metre in length. Although
this measurement is for fairly small fish, Webb (1975) discovered
that maximum acceleration rates for rainbow trout (40-50cm/sec2)
were in the same order for other fish from a wide range of sizes.
This suggested that maximum acceleration rates may be relatively
independent of size. Although acceleration and size may not be comparable
the wavelength of the body undulations remain constant when relative
to the body length within species. When the size of the fish increases
the attainable maximum frequencies decrease. In relation to tail
beats and swimming style, Webb (1991) found that over a period of
226 completed tail beats from trout no constant speed was registered.
Figure 5 shows the results and clarifies that sustained swimming
is never constant and will always involve acceleration, deceleration
Figure 5: Swimming styles compared to tail beats. Source
Webb (1991), p. 586
||The caudal fin is probably the most important attachment
used for acceleration. During Webbs (1977) experiment involving fin
amputation of rainbow trout he clarified that the large caudal fin
is required for maximum acceleration performance and creates the majority
of generated thrust during fast starts. The dorsal and anal fins are
also important in generating thrust but they are not as nearly as
significant. Some of the important aspects involving the movement
of trout have been discussed, finally but just as significant is the
production of energy needed to create these exercises. The thrust
force of the fish is produced by contractions of the propulsive musculature.
The velocity that the muscle contracts dictates the power that the
fish can produce.
|Muscle structures of fish can be split into white and red
types. Red muscle consists of up to 20% of the total belonging to the trout
(less for lower active species such as carp (Cyprinus carpio)). This
muscle has a low rate of fatigue and is used for all of the low speed sustained
cruising. The white muscle fatigues more rapidly but gives maximum power
output, which is used for burst speeds. Due to the speed of fatigue the
white muscle can be used only for short periods of time.
Blake, R.W. (1983). Fish locomotion. Cambridge university press,
Hoar, W.S., and Randall, D.J. (1978). Fish physiology, volume VII: Locomotion.
Academic press, New York.
Hosford, M.B. (1997). Fluid dynamics of ship resistance and propulsion.
Institute of marine studies, Plymouth.
Wardle, C.W., Videler, J.J., and Altringham, J.D. (1995). Tuning in to fish
swimming waves: body form, swimming mode and muscle function. Journal
of experimental Biology, Vol 198, p. 1629-1636.
Ware, D.M. (1975). Growth, metabolism and optimal swimming speed of pelagic
fish. Journal of the fisheries research board of Canada, Vol. 32,
Ware, D.M. (1978). Bioenergetics of pelagic fish: Theoretical change in
swimming speed and ration with body size. Journal of the fisheries research
board of Canada, Vol 35, p. 220-228.
Webb, P.W. (1975). Acceleration performance of rainbow trout (Oncorhyncus
mykiss). Journal of experimental Biology, Vol 63, p. 451-465.
Webb, P.W. (1977). Effects of median-fin amputation on fast start performance
of rainbow trout. Journal of experimental Biology, Vol 68, p. 123-135.
Webb, P.W. (1991). Composition and mechanics of routine swimming of rainbow
trout, (Oncorhyncus mykiss). Canadian journal of fisheries and
aquatic services, Vol 48, no. 4, p. 583-589.
Wilson, R.W., and Egginton, S. (1994). Assessment of maximum sustainable
swimming performance in rainbow trout. The journal of experimental biology,
Vol 192, no.1, p. 299-305.