A. Studies of Fishes

THE LIVING FISH

Vertebrates adapted to Water Life

Materials.

Living goldfishes or other fishes in small aquaria for individual study and a few fishes in a large aquarium where they have considerable freedom of motion.

Definitions.

Trunk, the portion of the body between the head and the tail. Compressed, a term used to describe the shape of the body when it is narrower from side to side than from dorsal to ventral surface. When the opposite is true, the body is said to be flattened. Median fins, the unpaired fins situated on the median line, dorsal and ventral, including the tail or caudal fin, the dorsal fin, and the anal fin. Paired fins, fins occurring in pairs of which the more anterior are the pectoral fins and the posterior are the pelvic fins. Fin rays, the framework or skeleton of the fins over which membrane is stretched to form the fins. Fin rays are of two kinds: those composed of bone and those composed of cartilage. Lateral line, a sense organ extending along each side of the fish in a line indicated by tubes or perforations in the scales. Gills, respiratory organs adapted for taking oxygen from the water. Operculum, the flaps covering the gills on each side of the head. Pigment, a substance which gives color to an object.

Observations.

Locomotion.

Watch the fishes in the large aquarium and determine which fins are most used and how they are used (a) in swimming forward, (b) in swimming upward and downward, (c) in maintaining balance, (d) in remaining at rest, and (e) in guiding the movements of the fish.
What advantages are there to the fish (a) in the power to open and close the dorsal and anal fins, (b) in having no neck, and (c) in having a compressed form?
Enumerate the various ways by which the body of the fish is adapted to rapid movement through the water.

What is the food of the fishes you are studying? Feed them and watch them eat. Why is the upper jaw often called a "lip"? What is the shape and size of the mouth when opened in feeding? Does the fish chew its food? Describe in detail the fishes' method of feeding.

Identify the opercula and the gill openings. Watch the movements of the opercula and mouth, and determine what movements are concerned in breathing and their order. Describe in detail the circulation of water used in breathing and how it is caused.

Identify the eyes, nostrils, and lateral line. How many nostrils are there and where located? What is the position and extent of the lateral line?
Describe the location of the eyes. What is the shape of the outer surface of the eyes? Why this shape? Can the eyes be moved, i.e. can they be rotated, rolled, or retracted? From what direction might an enemy approach without being seen? How would such an enemy be detected?

With what protective structures is the body covered? Do they hinder the movements of the fish? What are the advantages of the scale covering of fishes over the shell covering of grasshoppers or crayfishes?
In what other ways are the fishes you are studying protected against enemies? Since you cannot account for the red color of goldfishes on the basis of use to the fish, then how do you account for this bright color?

What is the symmetry of the fish? Into what regions is the body divided?

Summary of the study of the living fish.

Enumerate in one column the different adaptations which fit the fish for life in water and in a second column state the special purpose of each adaption.

The External Structure of the Fish

Materials.

Freshly killed or preserved fish in dishes or shallow pans with enough water to prevent drying. Simple or compound microscopes, forceps, and a bristle.

Directions.

Examine the fins and identify the membrane and the supporting rods, or rays, of bone or cartilage. Notice how the ends of the cartilaginous rays keep the membrane from tearing.

Investigate the scales as to their arrangement, number, and size. Remove a small patch of scales along the lateral line to find how they are attached, where the fish's color is situated, and how access to the sensory organs of the line is permitted. Examine a scale under the microscope.

Observe the eyes and identify the parts similar to those of the human eye: lid, lash, tear-duct, cornea, iris, and pupil.

In front of and between the eyes, find the nostrils. By means of a bristle determine whether these are connected and whether they do or do not open into the mouth or the throat.

Questions.

Make a list of the fins, classifying them according to their structure.
Bearing in mind the differences in structure and consequent action,—what can you say regarding the adaptation of the several fins for protection? for rigidity or flexibility in locomotion?
State how much of the body is covered with scales, and where the largest and the smallest ones are found.
How are the scales arranged with reference to each other? What benefit is derived from this in protection? in locomotion? If you have noticed any mucus or slime upon the body, state its use.
Do the scales or the skin bear the pigment? Give the color pattern of the kind of fish used in class. How would this be useful to the fish in its natural home?
Describe the structure of a scale and state how it is attached to the skin. In what way is the lateral-line scale specialized?
State how, when the fish is swimming, the nostrils catch odors. By means of a diagram, with arrows show the probable direction of the water current through the nose.
State which of the structures of your eye are present in the fish's eye, and which are missing. Could a fish weep? wink? How would a fish sleep?
Inasmuch as light penetrates water but a little way, so that objects can be distinguished only within about thirty feet, would the fish be nearsighted or farsighted?

Suggested drawings.

A side view of the entire fish, fully labeled.
A bony rayed and a cartilaginous rayed fin.
A scale, showing its minute structure.
A dorsal or a lateral view of the head, showing the sense organs.

The Mouth and the Gills of the Fish

Materials.

The same materials as those used in the preceding exercise may be used here.

Directions.

The mouth, its structure and its action, can be seen by pulling the upper jaw upward and forward until the mouth and the gill chambers open fully. Examine the structure and action of the jaws, the tongue, the throat, and the teeth on each jaw and on the roof of the mouth.

Investigate the breathing apparatus from the throat side and from the exterior, noting the number, form, and structure of the gills, their attachment and their protection.

The mouth may be kept open by a short splinter or a ball of paper.

The pupil should identify the following structures:—

1. Gill, an organ for breathing the air dissolved in water. 2. Gill arch, an arch of bone or cartilage supporting the gills. 3. Gill filaments, fringe-like structures attached to the gill arches, forming the gills. 4. Gill raker, lateral projections from the gill arches. 5. Gill-slits, openings between the gill arches for the passage of water. 6. Operculum, the flap-like covering of the gills on each side of the head.

Questions.

Compared with the size of its body, how wide can the fish open its mouth? What do you infer as to the size of its "bite"?
Are the jaws rigidly affixed to the skull? Why should they be so attached, or why not?
Of how many pieces is the upper jaw composed? the under jaw?
Where are the teeth? Judging from their form, size, and situation, what do you think must be their use?
Do you think the tongue is used to assist in mastication? in tasting? in speech? in swallowing?
How many gills are there, and where are they situated? How are they attached? Which one is not free from the body throughout its length?
What probably causes the color of the gill filaments? What is there in their number and texture which fits them for their function?
What is the direction of the water current through the gill chamber? Of what use are the gill rakers?
How are the gills protected?

Summary.

Write a complete account of how the fish eats and how it breathes.

Suggested drawings.

A front view of the fish's face, with the mouth fully open.
A side view, as above.
A ventral view of the head, with both gill-chambers wide open and the gills separated from each other. Indicate currents by arrows.
A single gill.

The Alimentary Canal and the Circulatory System of the Fish

Materials.

Small fresh fish, shallow pans or dishes of water, forceps, and scissors.

Directions.

If the instructor has not opened the fish previously, this is to be done by the student as follows: On the ventral side, insert the scissors in the vent (in front of the anal fin) and cut straight forward to a point between the opercula. Care must be exercised in opening the chamber about the heart; this lies between the gill chambers.

The various organs, so far as possible, should be carefully drawn out and separated, in order that their structure may be distinguished.

The pupil should identify the following parts:—

Body cavity, the entire internal space, divided by a membrane, false diaphragm, into a large abdominal cavity and a small chamber, pericardial chamber, between the gill chambers.
Liver, a large red or pink mass lying at the front end of the abdominal cavity, and divided into two unequal lobes. The gall-bladder, thin-walled and green, may be seen between these lobes.
Alimentary canal.
1. Mouth.
2. Esophagus, in the fish a very short tube.
3. Stomach, white and muscular, beginning with a very short esophagus and ending as a blind sac. If it is much distended, open it to see what the fish may have eaten.
4. Small intestine, thin-walled, tubular, and somewhat coiled.
5. Large intestine, a short, thin-walled expansion at the posterior end of the small intestine; usually less than half an inch long.
6. Cœca, from two to several small pouches attached where the small intestine leaves the stomach.
Spleen, a reddish brown globule between the folds of the intestine.
Swim bladder, an elongated chamber lying against the backbone, partitioned off from the cavity below by a delicate membrane.
Peritoneum, the delicate, silvery membrane which lines the abdominal cavity and enfolds the viscera. Note its spots of pigment.
Pericardial chamber, the chamber around the heart; see [§ 1] above.
Heart. As the fish is placed belly upward in the pan the ventricle faces you, pink, conical, and muscular. Posterior to it, on the dorsal side, is the auricle, a membranous sac.
Ventral aorta, arising on the anterior surface of the ventricle as a white muscular "cord" (really a tube) which is enlarged close to the heart into a bulb, the arterial bulb. You should follow up this aorta until you see it divide right and left to send its branches outward into the gills, the branches being called gill arteries.

Questions.

The fish frequently swallows its food alive. Why should the stomach be muscular? Why is it better that the intestine does not leave the stomach at the end opposite the esophagus?
Of what use can the cœca be? What structure of the human intestine do you recall that is at all like them in form or use?
How many times the length of the body is the length of the alimentary canal? Does this indicate that the fish is compelled to eat a great deal of poor food or that its food is highly nutritious, so that little need be taken?
Near which end of the fish's body is the heart? Is this the usual or the unusual condition among animals you know about? What advantages can you think of in this arrangement?
What advantages are there in having the heart in a chamber separated from the other vital organs?
Of how many chambers does the heart consist? Why should at least one of them be muscular?
How many times does the blood pass through the heart in making a complete circuit of the body? Would you call this a single or a double circulation?
Does the heart force the blood onward or does it draw blood into itself, i.e. is the heart a force pump or is it a suction pump?
How is circulation made complete? If the heart is a force pump, is its power sufficient to drive blood through artery, capillary, vein, and into auricle, if the capillaries can stand the pressure, or is another action concerned? If it is a suction pump, why does the blood leave the heart?

Suggested drawings.

The body cavity, with viscera undisturbed.
The alimentary canal extended.
The anterior end of the fish with the sinus held open, to show the general situation of the parts.
The heart in its chamber, with the outgoing vessels as far as dissected. Use arrows to show direction of circulation.
A copy of some good diagram or chart which illustrates the heart of the fish with the connecting veins and arteries.

Fishes: A General Review and Library Exercise

Food and the feeding habits of young and of adult fishes.
The diet and habits of cod; lantern-fish; swordfish; ramora; hagfish; angler; gar-pike; sturgeon; shark; sawfish; paddle-fish.
The variations, real or apparent, in the breathing habits of the porcupine-fish; the climbing-fish; the lung-fish.
Peculiarities in swimming as seen in the flying-fish; the flounder; the sea-horse.
Intensity of sound under water, and the corresponding structure of the fish's ear.
Light and sight under water (as in 5).
Protection of fishes: sting-ray; torpedo; coral-fish; sturgeon; lava-fish; swordfish; sawfish; pipefish.
The social instinct of fishes, and "schools."
The breeding habits of salmon; eel; stickle-back; sturgeon; whitefish; shark; sea-horse; sunfish.
The fishing industries of the Great Lakes or of the cold oceans, with a list of the fishes caught and their values.
Fish nets and traps: seine; gill-net; pound-net; trawl, French or English; fish-wheel; fish-weir; spear; dip-net; set-line; spoon; fly.
The U.S. Bureau of Fisheries: its locations, its problems, and its methods.
The State Fish Commission, as above.
Game and fish laws; their purpose and their enforcement.
Game fish of the fresh waters; trout, bass, pickerel, and muskellunge.
Game fish of the ocean: tarpon, tuna, sea-bass, swordfish, and bluefish.
Fish as food.
Fish diet and leprosy.
Fish diet and parasitic worms.
Fish nuisances: carp, catfish, and dogfish.
Commercial products of fishes, their preparation and their uses: caviar, shagreen, cod liver oil, isinglass, and glue.
The geographic distribution of fishes, with means of dispersal and restriction.
The faunal regions of the lake (or ocean), with characteristic forms.
Fishes of ancient times; of the Devonian period.
The story of the early life of Louis Agassiz; of D. S. Jordan; of C. H. Eigenmann; of Bashford Dean.
Goldfish: their origin; how to care for them.
Fashions in fish tails, old and new.
Development and variation in scales; fashions in scales.
The common orders of fishes, with examples.

Primitive Chordates

Materials.

An acorn-tongued worm, a lancelet, a lamprey, a shark, and a perch. If individual specimens are not available, the pupil's text-book and charts are to be used.

Observations.

Acorn-tongued worm: Notice the very simple form and structure of the symmetrical body, the "proboscis," the collar surrounding the neck with its simple rod of cartilage, the marks of internal gills and gill slits extending some distance along the body, and the presence or absence of sense organs. The acorn-tongued worm (Balanoglossus) lives in the sand of the seashore and in shallow water in temperate and tropical regions. Lancelet: Observe the form of the body, of the fin, and of the mouth; note the presence or absence of sense organs, and find out the number of gills or gill slits. The lancelet (Amphioxus) is similar in habit to the acorn-tongued worm. By day it lies buried with only the mouth exposed, but at night it swims actively about. It is somewhat more confined to the tropics. Lamprey: Observe here also the primitive or unspecialized form of the body, of the fin, of the jawless mouth, the number of gill slits, and the sense organs. Shark: Examine the body, noting its form and differentiation into regions, its covering, its fins, mouth, gill slits, and sense organs. Perch: If you have not already studied the bony fish, the points suggested for the shark will be sufficient for this exercise.

In each case, find out the condition of the skeleton.

Questions.

Which of these animals seem most simple in form, and which most complex? Give a reason for your answer.
Give the stages which show how the fold of skin develops into separate fins.
How does the number of gills and gill slits change in the series? (Give definite numbers.) How may the reduction in the number of gills be compensated for in the amount of surface exposed for the exchange of gases in breathing?
How is protection afforded the delicate structure of the gills in the final form?
Give the stages in the formation of a definite, symmetrical mouth with jaws of equal size.
The presence of sense organs may be taken to indicate that there is an organ of control, or brain. How is the development of this organ like or unlike that of the other structures in the series?
For the developing brain and nervous system what protection and support is afforded in each case?

The foregoing questions may be answered in tabular form by arranging the names of the animals in a line and the questions in a column.

Suggested drawings.

Acorn-tongued worm, × 1.
Lancelet, × 1.
Lamprey, × ½.
Shark: 1, head as far as the pectoral fins; 2, the tail.
Perch, as directed for shark.