The Stickleback

Teacher’s Story

HIS is certainly the most sagacious of the Lilliputian vertebrates; scarcely more than an inch in length when full-grown, it gazes at you with large, keen, shining-rimmed eyes, takes your measure and darts off with a flirt of the tail that says plainly, “Catch me if you can.” The sticklebacks are delightful aquarium pets because their natural home is in still water sufficiently stagnant for algæ to grow luxuriously; thus we but seldom need to change the water in the aquarium, which, however, should be well stocked with water plants and have gravel at the bottom.

When the stickleback is not resting he is always going somewhere and he knows just where he is going and what he is going to do, and earthquakes shall not deter him. He is the most dynamic creature in all creation, I think, except perhaps the dragon fly, and he is so ferocious that if he were as large as a shark he would destroy all other fishes. Place an earthworm, cut into small sections, in the aquarium and while each section is wriggingly considering whether it may be able to grow both ends into another worm, the stickleback takes hold with a will and settles the matter in the negative. His ferocity is frightful to behold as he seizes his prey and shakes it as a terrier does a rat.

Well is this fish named stickleback, for along the ridge of its back are sharp, strong spines—five of them in our tiny, brook species. These spines may be laid back flat or they may be erected stiffly, making an efficient saw which does great damage to fish many times larger than the stickleback. When we find the minnows in the aquarium losing their scales we may be sure they are being raked off by this saw-back; and if the shiner or sunfish undertakes to make a stickleback meal, there is only one way to do it, and that is to catch the quarry by the tail, since he is too alert to be caught in any other way. But swallowing a stickleback tail first is a dangerous performance, for the sharp spines rip open the throat or stomach of the captor. Dr. Jordan says that the sticklebacks of the Puget Sound region are called “salmon killers” and that they well earn the name; these fierce midgets unhesitatingly attack the salmon, biting off pieces of their fins and also destroying their spawn.

As seen from the side, the stickleback is slender and graceful, pointed like an arrow at the front end, and with the body behind the dorsal fin forming a long and slender pedicel to support the beautifully rounded tail fin. The dorsal fin is placed well back and is triangular in shape; the anal fin makes a similar triangle opposite it below and has a sharp spine at its front edge. The color of the body varies with the light; when floating among the water weed the back is greenish mottled with paler green, but when the fish is down on the gravel it is much darker. The lateral line is marked by a rather broad silver stripe.

If large eyes count for beauty, then the stickleback deserves “the apple,” for its eyes are not only large but gemlike, with a broad iris of golden brown around the black pupil. I am convinced that the stickleback has a keener vision than most fish; it can move its eyes backward and forward rapidly and alertly. The mouth opens almost upward and is a wicked little mouth, both in appearance and action.

When swimming, the stickleback darts about rapidly, its dorsal and anal fins extended, its spines all abristle, its tail lashing the water with strong strokes and the pectorals flying so fast that they make a blur; the ventral fins are rarely extended, in fact they are nothing but two little spines. When the fish wishes to lift itself through the water it seems to depend entirely upon its pectoral fins and these are also used for balancing. Its favorite position is hanging motionless among the pond weeds, with the tail, the dorsal and ventral fins partially closed; it usually rests upon the pectoral fins which are braced against some stem; in one case I saw the ventrals and pectorals used together to clasp a stem and hold the fish in place. In moving backward the pectorals do the work, with a little beckoning motion of the tail occasionally. When resting upon the bottom of the aquarium, it closes its fins and makes itself quite inconspicuous. It can dig with much power accomplishing this by a comical augerlike motion; it plunges head first into the gravel and then by twisting the body and tail around and around, it soon forms a hiding place.

But it is as a house builder and father and home protector that the stickleback shines. In the early spring he builds him a nest made from the fine green algæ called frog-spittle. This would seem a too delicate material for the house construction, but he is a clever builder. He fastens his filmy walls to some stems of reed or grass, using as a platform a supporting stem; the ones which I have especially studied were fastened to grass stems. The stickleback has a little cement plant of his own, supposed to be situated in the kidneys, which at this time of year secrete the glue for building purposes. The glue is waterproof. It is spun out in fine threads or in filmy masses through an opening near the anal fin. One species weights his platform with sand which he scoops up from the bottom, but I cannot detect that our brook stickleback does this. In his case, home is his sphere literally, for he builds a spherical house about the size of a glass marble, three-quarters of an inch in diameter; it is a hollow sphere and he cements the inside walls so as to hold them back and give room, and he finishes his pretty structure with a circular door at the side. When finished, the nest is like a bubble, made of threads of down and yet it holds together strongly.

In the case of the best known species, the male, as soon as he has finished his bower to his satisfaction, goes a-wooing; he selects some lady stickleback, and in his own way tells her of the beautiful nest he has made and convinces her of his ability to take care of a family. He certainly has fetching ways for he soon conducts her to his home. She enters the nest through the little circular door, lays her eggs within it, and then being a flighty creature, she sheds responsibilities and flits off care free. He follows her into the nest, scatters the fertilizing milt over the eggs and then starts off again and rolls his golden eyes on some other lady stickleback and invites her also to his home; she comes without any jealousy because she was not first choice, and she also enters the nest and lays her eggs and then swims off unconcernedly. Again he enters the nest and drops more milt upon the eggs and then fares forth again, a still energetic wooer. If there was ever a justified polygamist, he is one, since it is only the cares and responsibilities of the home that he desires. He only stops wooing when his nest holds as many eggs as he feels equal to caring for. He now stands on guard by the door, and with his winnowing pectoral fins, sets up a current of water over the eggs; he drives off all intruders with the most vicious attacks, and keeps off many an enemy simply by a display of reckless fury; thus he stands guard until the eggs hatch and the tiny little sticklebacks come out of the nest and float off, attaching themselves by their mouths to the pond weeds until they become strong enough to scurry around in the water.

Some species arrange two doors in this spherical nest so that a current of water can flow through and over the eggs. Mr. Eugene Barker, who has made a special study of the little five-spined sticklebacks of the Cayuga Basin, has failed to find more than one door to their nests. Mr. Barker made a most interesting observation on this stickleback’s obsession for fatherhood. He placed in the aquarium two nests, one of which was guarded by its loyal builder, which allowed himself to be caught rather than desert his post; the little guardian soon discovered the unprotected nest and began to move the eggs from it to his own, carrying them carefully in his mouth. This addition made his own nest so full that the eggs persistently crowded out of the door, and he spent much of his time nudging them back with his snout. We saw this stickleback fill his mouth with algæ from the bottom of the aquarium, and holding himself steady a short distance away, apparently blow the algæ at the nest from a distance of half an inch, and we wondered if this was his method of laying on his building materials before he cemented them.

The eggs of this species are white and shining like minute pearls, and seem to be fastened together in small packages with gelatinous matter. The mating habits of this species have not been thoroughly studied; therefore, here is an opportunity for investigation on the part of the boys and girls.