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The Origin of the Habit of Oral Gestation

nest, eggs, mouth, fish and time

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THE ORIGIN OF THE HABIT OF ORAL GESTATION.

The causes leading to the practice of buccal incubation are plainly set forth in the preceding section; the eggs must be guarded in a nest or carried in the mouth, or else the fish would soon become extinct. The gaff-topsail has chosen the latter means to maintain itself. But how has the habit been developed? The answer to this is largely conjectural, but there is a fair amount of data to be adduced upon which to base our conjecture.

It has long been known that some fishes pick up their eggs or young in their mouths for transport from place to place much as a cat does her kittens or a fox her cubs. The writer believes that in this habit are to be found the beginnings of oral gestation. The fishes referred to are members of the families Gasterosteidte and Osphromenidze, together with one or two other isolated forms.

The first account to be given is the classic one of Coste, " Nidifi cation des Epinoches et des Epinochettes," published in 1848. After describing the making of the nest and the laying of the eggs, Coste tells how the male Gasterosteus pungitius stands watch and ward over the nest until the eggs are hatched, hastening the process by fanning them free of sediment and by helping in their oxygenation at the same time. When hatched, "He does not allow the young to go outside the boundaries of the nest, and if any one does so, he takes it in his mouth and bears it immediately back to its domicile. If, however, the number of deserters increases, he seizes several at one time without hurting them." With regard to the question of feeding during this self-imposed guardianship, Coste adds: "This animal, which during all the remainder of the year is remarkable for its voracity, suffers an abstinence almost complete during the time devoted to the construction of its nest, the care of its eggs, and the training of its young." An almost equally charming account is that of Albany Hancock (1854) for Gasterosteus aculeatus and G. spinachia. In most interesting fashion he describes how he saw the watchful parent with gaping jaws seize the little wanderer, who disappeared therein, as he thought, forever. But to his delight the old fish returned to the nest and deposited the small straggler therein. Then he saw that it was the purpose of the paterfamilias to allow no rambling from the nest. Sometimes the fry were held in the mouth for an appreciable length of time, but they were never harmed.

A similar state of affairs was noted for Gasterosteus leiurus by Robert Warrington in 1855. After describing the building of the nest, he says that as the yolk-sacs of the developing young become smaller and their activity greater, "their attempts carried them to a great distance from the parent fish; his vigilance, however, seemed every where, and if they rose by the action of their fins above a certain height from the shingle bottom, or flitted beyond a certain distance from the nest, they were immediately seized in his mouth, brought back and gently puffed or jetted into their place again."

Furthermore, if the fishlets are removed by artificial means the father brings them back in his mouth and shoots them into the nest, according to the observations of William Houghton, recorded in 1865. Ransom, in the same year noted the same habit and says of G. pun gitius: "He seemed to take no food." "The Tinker was almost starving in the midst of plenty." Nor are later observations of this habit lacking if one may credit Becker's notes on G. aculeatus pub lished in 1907.

Almost in the Antipodes, we find certain osphromenid fishes prac ticing similar habits. Many of these make floating nests of foam and mucus in which the male guards the eggs and young. The first account is from the pen of the indefatigable French aquarist of the third quarter of the last century, P. Carbonnier. Describing a Chinese macropode (1869, 1869a), he writes of the male that, after extrusion and fertilization of the eggs: "He patiently gathers in his mouth the eggs scattered on all sides and carries them under the roof of foam which becomes then for some ten days the object of his solicitude. Without even taking food, he passes his time in watching over the receptacle of his progeny. If one part of the nest begins to empty itself he fills it with new bubbles; he withdraws the eggs where they seem to him to be in too great numbers and carries them into empty places; with blows of his head he disperses the eggs if too much accumulated. When hatching is over he watches with some care over the young embryons; he chases down those which leave the protecting roof, and holding them in his mouth brings them back. He does not cease this surveillance until the too large number of fugitives announces to him that his part is played and that the young family is able to look after its own protection." Again, in 1872 Carbonnier described similar habits for a " Macropode of China," which may or may not have been identical with the fish described above. In this case, however, both the male and the female took up the young. "I saw the female place in the mouth of the male the slender little [sick] fry which would have certainly perished without intelligent paternal care." Some years later Car bonnier (1875, 1876) describes how the paternal rainbow fish, Colisa arc-en-ciel, collects the scattered eggs and embryos in his mouth and transports them to the nest.

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