Popular Science Monthly/Volume 9/July 1876/The Chromis Pater-Familias
By Dr. LORTET.
UP to the present we know but a small number of fishes which hatch their eggs and bring up their young in the cavity of the mouth or among the gills. Agassiz, during his voyage on the Amazonas, discovered one species. Afterward there was brought from China the macropod, the singular habits of which are now known to all the world. All these species belong to the great group of the Labyrinthobranchiata; and Agassiz supposes that the fishes of this order only can hatch their eggs in so abnormal a manner, thanks to the branchial pockets which allow of the eggs being easily kept in place. But the Chromis, of which we give a faithful representation, proves the assertion of Agassiz to be erroneous. The Chromis pater-familias has the gills disposed in simple laminæ; it is unprovided with any special apparatus for retaining the eggs or the young ones, and yet it brings up about 200 young in the mouth and gills. It is always the male that performs these functions of incubation. After the female has deposited the eggs in a depression of the sand or between the tufts of reeds, the male approaches and takes them by inhalation into the cavity of the mouth. From there some movement, the mechanism of which we have not been able to observe, sends them between the leaflets of the gills. The pressure exerted on the eggs by the branchial laminæ suffices to keep them in place. There, in the midst of the organs of respiration, the eggs undergo all their metamorphoses. The young ones grow rapidly, and soon appear much inconvenienced in their narrow prison. They leave it, not by the gills but through the opening by which the bronchial cavity communicates with the mouth. Here they remain in great number, pressed against one another like the seeds of a pomegranate. The animal's mouth becomes so distended by the presence of this numerous progeny that actually the jaws cannot meet. The cheeks are swollen and the animal
Chromis Pater-familias of Lake Tiberias.
presents the strangest aspect. Some of the young, arrived at the perfect state, continue to live in the gills. All have the head directed toward the buccal opening of the father, the protecting cavity of which we have not seen them leave even for a moment. Though so numerous, they hold their ground very firmly, yet how they do so we have not discovered. Neither can we understand how the nursing lather avoids swallowing his progeny; we are also ignorant at what period of their life the young ones leave the paternal mouth to live independently.
The Chromis pater-familias is 7 inches long by 13 inch thick. The teeth are very fine and sharp, disposed in several rows. The snout is obtuse, conical, the upper profile oblique. The nasal prominence is very conspicuous. The caudal fin is almost truncated. The soft rays of the dorsal reach to the beginning of the caudal. The length of the body, including the tail, is 41 times its thickness. The snout is in length twice the diameter of the orbit. The mouth is slightly oblique, large, as wide as it is long. The teeth are slightly recurved, disposed in three or four rows, tinged with deep yellow at the free end. The first row presents 26 on each side of the upper maxillary. The fins show the number of rays following:
The lateral line comprises 32 scales disposed 20+12. The scales are cycloidal, their length greater than their breadth; three-fourths of their surface is covered by the succeeding scales. Color, olive-green on the back, barred with blue. The belly has a silvery lustre, with green and blue spots.
I caught this interesting species, with a net, on the 29th of April, 1875, in shallow water full of reeds, on the margin of Lake Tiberias, at a place called Ain-Tin, the ancient Capernaum. There are numerous warm springs there which unite to form a rather considerable stream. It is in these warm waters that the Chromis lives.—La Nature.