Masked Butterflyfish (Chaetodon
Semilarvatus)
1. Details
Name: Masked Butterflyfish
(Chaetodon Semilarvatus) belongs to the family Chetodontidae.
Habitat: The Red Sea. The adults
live in pairs at constant areas in the front of reefs. Its menu includes mainly coral polyps. It sometimes rests without motion
in hide places.
Description: Its body is flattened and high. Its length is 15-23 cm from head
to base of tail. The tail is 2 cm long. The color of its body is yellow with 13-14 brown-orange height bands. It has a gray
stain which seems as a cheek. (Therefore, its name in Hebrew is "Parperon Afor-Lechy").
Reference:
D. Golani and D. Darom, Handbook of the Fishes in Israel, Keter Publishing House Ltd. 1997 (In Hebrew). p.78].
2
Physical Explanations
2.1 Mechanical considerations:
The
body is flattened and high. This allows this ship to go into narrow and long cracks in the reef . The main color of
the body is yellow. In BioColorPhysics the Yellow color is correspondence with the mechanical property: "Shearing
Stiffness". Shearing strains occure when two oppsite forces are emploied on adjacent points of the skin, in
this case. Shearing Stiffness means the skin will not be torn due to Shearing strains. The
existance of Yellow skin in this fish and in other kinds of Butterflyfihes, hints that there are a lot of small vortices
in the zone of these fishes abitat. This is reasonable conclusion when considering the many small vortices
due to streams of water through the branches of the corals in the reef.
There are also 13-14 brown-orange height bands in the body of the Masked Butterflyfish.
This might be due to addition of Red and Black colors to the Yellow skin, at those bands. In BioColorPhysics, the Mechanical
property correspondence to Red is "Bending Elasticity", and to Black is "Tension Stiffness". Thus, those
Brown-orange bands hints that along those bands there is addition of Bending and Tension strains. A source to such
additional strains might be while this fish bends somewhat its body to the sides. The flattened body means there is
no havy layer between the inside bones and the skin. Thus, when the body of this fish bends to the side, the
skin in the center of the body might be stretched somewhat. The addition of the Red may allow the Bending Elasticity
of the skin along those bands. The addition of Black may add Tension Stiffness in those bands.
It is remarkable to note that a Black band exists at the tip of the tail of this fish.
There is no doubt that the tip of the tail sustains tension stresses while the tail move to left and right. The tail behaves
essentially in the water as a flag in the wind. You may notice that flags are sometimes torn at their edge when they are too
long time in a strong wind. In principle what matter is the relative velocity between the flag and the air. For understanding
this, let us suppose we have a flag that it is not tied to a constant point in the ground and it can be free to move from
side to size. Suppose the air is still, i.e. there is no wind. Suppose also that the flag floats in the air. Now let this
flag move from side to side at a specific frequency, F. Therefore, the flag will advance at a specific speed, V. Now let stop
the flag and tie it to the top of a stick while its lower end is in the ground. If we push an air in the direction of the
flag while the wind velocity is the same V, then the frequency of the flag will be the same F. This principle of relative
velocity is the base to many aerodynamic and hydrodynamic experiments. All this was explained in order to convince that the
edge of the tail of the fish has the same problem as the edge of the flag. They both sustain tension stresses. The addition
of Black color to the edge of our fish's tail hint about the solution that Nature found to this problem.
The Mechanical properties corresponding to the Gray color, in BioColorPhysics, are
"Crush Elasticity" plus "Tension Stiffness". The Gray stain on the cheek of the Masked Butterflyfish hints that this
area may sustain crush and tension stresses. We notice from the picture that this stain is at the continuation of the eye.
This may hint that while this fish moving its eye, the skin close to the eye is crushed or stretched. This is not the
case with our eyes, since our eyeball imbedded totally inside a hole in our skull. For looking backwards without turning the
whole body we turn the head by 90 degree. This is due to our flexible neck. However, fishes do not have a neck. A neck
could cause high hydrodynamic drags while the fish swims. Thus, for looking backwards, the eyeball of the fish is somewhat
out of the skull. Therefore, the skin is effected by the movements of the eyeball. When the eyeball moves it pulls
or pushes the edge of the skin close to it. The geometry of the Gray stain in this fish may hint about the following.
Let us say that the motions of the eyeball forewords and backwards leads to a medium level of crushing and stressing of the
skin. Then, the motion downward leads to a lower level while the motion upward leads to higher level. This may hint that
this fish looks upwards more than downwards. It is plausible that this fish's head is more downwards, while foraging for coral
polyps, than upward. All this may hint that while the head of this fish is downwards the fish looks not only downwards but
also in the horizontal direction, i.e. upwards of his head.
It is amazing, even for me, to find out so many
hints from a simple stain, by using BioColorPhysics. I hope biologists will search this subject
and see which of those hints are true.
2.2 Thermal Considerations
The main color of this fish is Yellow, which is corresponding, in
BioColorPhysics, to the Thermal Property "Heat Conservation". How we explain this. Let us recall that this fish, Masked Butterflyfish, forages for coral
polyps in the front of the reef. Usually this means shallow water. In addition, the foraging is during the day hours
in the Red Sea, which is usually sunny. Therfore, it seems reasonable that this fish absorbs and conserve the sun rays while
the fish is exposed to the sun, in order to keep the temperature of the body, between certain limits, when the fish goes
in and out between the coral branches and cracks which supply places that are not exposed to direct sun and therefore the
temperature there is lower than outside of the shades.
The Gray stain in the continuation of the eye is interesting not only
due to the Mechanical characteristics discussed above, but also due to the Thermal characteristics, as we explain now. Gray
color corresponds, in BioColorPhysics, to "Cold Insulation" plus "Heat Insulation". Therefore, this enable
to suggest that the Gray stain protects the inside part of the eyeball from excess of Cold or Heat. As we know from Hi-Tec technology
of vision, the sight sensors should be kept within significantly different temperature than the temperature of
the observed object. For instant, when a snake uses its InfraRed eye for detecting the hot body of a rat inside a cave, the
temperature of the cave, and thus of the infrared sensor of the "cold blood" snake, is lower than the temperature of the body
of the "hot blood" rat. When the snake and the rat are both outside the cave in sunlight, the snake may not be
able to observe the rat by the infrared eye. For this purpose the snake should use its usual eyes. The same
principle may hold in the case of the Masked Butterflyfish. The polyps should are probably at about the same temperature
as the water. The fish is "cold blood". Therefore, its' body temperature is also about the temperature of the water.
If the eyeball is not insulated from the temperature of its surrounding, including the hot sunrays or the coldness of the
coral cracks, this fish might have difficulties to observe its menu. Thus, the Gray stain in the continuation of the
eye hints that this stain insulates the inside eyeball from too cold or too hot temperatures.
There are many animals, specially those with "cold blood" that have
special stains near the eyes. The explanation here may explain those stains as well.
