What Is A Fish? (1963)

what exactly are these animals that live and die in a watery environment habits and characteristics in short just what is a fish the fish that are alive today fall into three major groups skates and rays and the Bony fishes such as the Herring we'll start with the most primitive of all the lampri and hagfish they have no limbs or Jaws only a round hole for a mouth although they have a backbone it is not made of bone but flexible cartilage without Jaws they feed by attaching their mouths to their prey rasping Holes In the Flesh with Barb tongues and then sucking out the tissue that is being dissolved by their saliva to reach the evolutionary stage of typical fishes two great advances had to be made over the structure of the lampas biting jaws and paired fins with the Advent of the Sharks and skates and the various types of rays the vertebrates had gained jaws and teeth now instead of being mere scavengers of the bottom they could prey on the other active creatures of the water one can get some idea of how Jaws might have developed by opening up the Gill area of a shark these are the sharks Jaws notice the amazing similarity to the Gil bars as you can see it is more than probable that the Jaws are derived from a pair of these Gil bars that have become adapted to to carry out this new function you are now looking at a magnified view of a shark's skin the little plates are called denticles and are essentially the same structure as the shark's teeth it is probable therefore that the teeth of a shark were derived from tacles present in the skin of the mouth the tentacles have merely become enlarged and been used in a new way with jaws and teeth the Sharks also develop the ability to move faster in pursuit of their prey as in all typical fish their propulsion is by sideways undulations of the body except for the skulling action of the tail fin the fins are not used for propulsion instead the shark uses them for steering and a stabilizers to prevent Rolling In The Water the Lam pris and sharks have skeletons of cartilage but the remaining group of fish are the bony fish with backbone and skeletons actually made of bone the modern bony fishes are divided into two distinct types the ray fins and the lobe fins in the ray fin fishes the fins are composed of only a thin web of skin that is supported by Rays on the the other hand the lob fins like the cican have actual limbs for they have a fleshy lobe supported by a skeleton of bone the Strang looking cants were believed to have been extinct since the age of dinosaurs however in 1939 one was caught alive off the African Coast since then others have been netted and intensively studied the other type of living lob fins are the lung fishes lung fishes are found in only three small areas of the world but within their limited environment they are well adapted for in the stagnant pools where the lungfish live nearly all other fish would die for lack of oxygen however the lungfish actually possess lungs and rise to the surface to breathe air nowaday days there are very few cants and lung fishes and from an evolutionary point of view it is the rins that have been particularly successful one of the factors that has been responsible for the success of the renss are the fins themselves a thin web of skin supported by Rays these give the fish much greater maneuverability in the water the scales of most fishes are flexible overlapping plates they give protection while being light enough and flexible enough to allow the fish to swim freely through the water fishes take their oxygen from the Water by means of gills water taken in through the mouth passes out over the red Gill filaments rich in blood the filaments are able to absorb the oxygen from the water if we open the fish we can see the position of the Hut it lies just back of the gills and pumps the blood through the Gill filaments inside the fish's mouth are a series of tooth-like Bones which act as a basket to hold and channel of food down the throat cutting open the throat area we can see that the food will pass from the throat directly into the stomach in fact from the throat it is a long continuous tube through the stomach and the intestines until finally waste products are emitted at the anus in modern rafin The ancestral lung has been transformed into a swim bladder this is a strong membrane filled with gas and is similar to the buoyancy tank of a submarine by varying the amount of gas a fish can remain buoyant at different depths it simply floats in the water if one filet a fish the fleshy part that one eats are the muscles the rigid yet flexible backbone gives a Firm support for the action of these muscles and so most fishes are very fast and agile the rins are found all over the world and live both in fresh waterer and in the ocean comprising over half of all vertebrate species they have developed an enormous variety of body characteristics the trunk fish for instance has burn Pony plates under its skin giving it a completely rigid body the file fish a bottom feeder often drifts around in a vertical position well camouflaged the trumpet fish will quietly stalk its prey among the eelgrass or alternatively float head down and wait for a prospective victim by concealing itself in a group of finger sponges and this rock over which the little striped fish are swimming is actually a scorpion fish the arowana is a mouth breeder the fertilized eggs being stored and hatched in its mouth usually swimming near the surface of the water its oblique mouth is well adapted to scooping up food from underneath while some fishes browse on the algal plant and brial zones that grow over the surface of coral waths the remarkable looking seahorse moves through the Water by rapidly undulating a fin on its back like this pipe fish they have swiveling binocular eyes these enable them to accurately judge the distance of their minute prey and suck it into their tube likee snouts apart from their widely differing physical characteristics the rafin also show remarkable Variety in their behavior patterns these grunts appear to be kissing but in reality it is probably a threatening pose when one fish intrudes on the privacy of another jawfish have a particularly interesting adaptation to life in the water in that they live in Burrows that they dig and line with stones however when one jawfish digs a burrow too near another the fish that was there first appears to resent this intrusion of its territory and is determined to force The Interlopers evacuation the first step in its campaign to intimidate the other jfish is to steal the stones that are around the doorway and to use them to build up a it own nest naturally the newcomer resents this Pary but as in most cases in nature the larger or alternatively the more aggressive animal usually wins the argument between the two soon results in an aggressive display finally the original inhabitant of the territory seems to feel it necessary to drive the interloper away it invades the neighboring burrow the newcomer is forced to evacuate the Victor then returns to its own hole and snaps at the defeated rival the puffer fish scares off its enemies by enlarging its body with water this causes its quills to stand erect and provides a formidable deterrent to any aggressor when the danger is passed the puffer gradually returns to its original more streamline shape but not all fish are as well endowed with such a protective device and predation by one fish on another is a constant danger in this world of the waters apart from this direct approach there are some fishes that employ an Artful Gile the Anglers for instance in addition to a deceptive camouflage actually go fishing they have a highly specialized spine and when they are hungry they extend a bony filament from their head to act as a fishing pole at the the end of the pole is their bait a fleshy appendage which they vibrate making it look like a wriggling worm small fish attracted to the bait are taken in a mouthful the queen trigger is a fish that will eat almost anything algae Coral mollus even a spiny sea urchin makes an acceptable meal but killing an urchin is not a simple operation it will try to wedge itself between a crack in the rocks and it has very sharp spines the trigger keeps pulling it back into the open then it carries it up into the water and drops it if the urchin lands on its back the trigger will move into the attack for the sharp spines are shorter on its Underside however the urchin keeps managing to write itself until finally it is not quite fast enough quickly the trigger smashes a hole in it with powerful jaws it does not take long to eat out the urchin soft insides soon there is only a hollow shell surrounded by the now useless spines one of the interesting commensal relationships is that of the shrimp and the goby for they both occupy the same burrow while the the shrimp shovels dirt out of the hole like a small bulldozer the goby stays quietly at the entrance but always on the alert for danger dancing enticingly and wriggling its antenna the little parasite picking shrimp signals that it is hungry fishes come and settle quietly on the bottom to have the parasites clean from their scales they hold themselves quite rigid and even open their Gill covers so that the shrimp can get underneath to seek out and eat the parasites these shrimp have definite stations and often several fish will line up for this cleaning job at the same time then there are fish that clean other fish little line goes that have what appears to us the invidious task of cleaning the parasites off such dangerous creatures as the vicious looking moray eel however the the mé has no use for the go beia's food and is much more interested in having its irritating parasites removed when cautiously approached some fish are somewhat similar to squirrels in the park and are apparently quite content to be handled unlike most of the animals of the land they do not seem to fear man's presence whether they actually respond to affectionate handling or whether they are merely inquisitive is not yet known in most fish the process of reproduction follows this General pattern first the relatively elaborate coting procedure as in the coting of these angel fish this induces the female to lay her eggs the eggs of these sergeant major fish have a purplish color and cover the Rocks after the eggs are laid the male swims over them and fertilizes them and sometimes the male will stand guard over the eggs until they are hatched these tiny freshwater fish are Arius lapus the female has just started to spawn the development of a single egg cell into a whole fish f is a fascinating process and a study of this process helps us to gain new insight into vertebrate embryology the eggs of these small fish are as transparent as glass beads and are therefore ideal for microscopic study here are the eggs before fertilization the sperm look like tadpoles their size about 3 1,000 of a millimeter the sperm cells move briskly about the egg this is the minute opening where the sperm will enter a sperm cell penetrates the egg another tries to follow but it will be shut out only the first sperm to enter the egg will affect fertilization following fertilization there is a rapid change in the egg's protoplasm the globules of oil which serve as nutrients during later stages of development fuse and move downward while the protoplasm gathers at the upper end of the egg to form what will become the pre-embryo the first cleavage or cell division of the egg now takes place the pre-embryo continues dividing into numerous cells then gradually spreads over the yok 26 hours have elapsed the developing embryo has now covered 3/4 of the egg and a rhythmic movement has begun 36 hours after fertilization some of the new cells have gathered together to form two parallel lines these lines indicate the border of the neural tube which eventually develops into the brain and the spinal cord the top end of the neural tube bulges into two directions to become the eyes The Space Between the Eyes is the developing brain 50 hours after fertilization the heart is merely a small tube and beating very faintly but no blood is running through it since the blood vessels have not yet been formed 56 hours after fertilization the cells near the heart undergo a change and begin to form blood vessels blood cor pusles are rapidly increasing in the region and suddenly the blood begins to flow into the heart and circulation Begins the heart beats powerfully as the blood is pumped through the body it carries with it the nutrients that will accelerate the growth of new organs by the seventh or Eighth Day the body is almost complete with all the internal organs ready to function the 10th day the embryo is now moving briskly within its enveloping membrane the 11th day the embryo breaks out of the shell and a new aresius latius has been hatched the young fry will become an adult fish in 3 months then it too will begin spawning what is a fish there is no simple answer but we can say that it is an active swimming creature with a backbone and that it is characterized by having fins and scales we might add that fishes exhibit interesting and complex Behavior patterns and abound in such variety that their species outnumber all other vertebrates combined all these factors and more add up to an extremely successful animal the fish