A Guide to the Study of Fishes, Volume 2 (of 2)

by David Starr Jordan

The Pine-cone Fishes: Monocentridæ.—Among the most extraordinary of all fishes is the little family of Monocentridæ, or pine-cone fishes. Monocentris japonicus, the best-known species, is common on the coasts of Japan. It reaches the length of five inches. The body is covered with a coat of mail, made of rough plates which look as though carelessly put together. The dorsal spines are very strong, and each ventral fin is replaced by a very strong rough spine. The animal fully justifies the remark of its discoverer, Houttuyn (1782), that it is "the most remarkable fish which exists." It is dull golden brown in color, and in movement as sluggish as a trunkfish. A similar species, called knightfish, Monocentris gloriæ-maris, is found in Australia. No fossils allied to Monocentris are known.

CHAPTER XVI
PERCOMORPHI

Suborder Percomorphi, the Mackerels and Perches.—We may place in a single suborder the various groups of fishes which cluster about the perches, and the mackerels. The group is not easily definable and may contain heterogeneous elements. We may, however, arrange in it, for our present purposes, those spiny-rayed fishes having the ventral fins thoracic, of one spine and five rays (the ventral fin occasionally wanting or defective, having a reduced number of rays), the lower pharyngeal bones separate, the suborbital chain without backward extension or bony stay, the post-temporal normally developed and separate from the cranium, the premaxillary and maxillary distinct, the cranium itself without orbitosphenoid bone, having a structure not greatly unlike that of perch or mackerel, and the back-bone primitively of twenty-four vertebræ, the number increased in arctic, pelagic, or fresh-water offshoots.

The species, comprising the great body of the spiny-rayed forms, group themselves chiefly about two central families, the Scombridæ, or mackerels, and the Serranidæ, the sea-bass, with their fresh-water allies, the Percidæ, or perch.

The Mackerel Tribe: Scombroidea.—The two groups of Percomorphi, the mackerel-like and the perch-like, admit of no exact definition, as the one fully grades into the other. The mackerel-like forms, or Scombroidea, as a whole are defined by their adaptation for swift movement. The profile is sharp anteriorly, the tail slender, with widely forked caudal; the scales are usually small, thin, and smooth, of such a character as not to produce friction in the water.

In general the external surface is smooth, the skeleton light and strong, the muscles firm, and the species are carnivorous and predaceous. But among the multitude of forms are many variations, and some of these will seem to be exceptions to any definition of mackerel-like fishes which could possibly be framed.

The mackerels, or Scombroidea, have usually the tail very slender, composed of very strong bones, with widely forked fin. In the perch and bass the tail is stout, composed largely of flesh, the supporting vertebræ relatively small and spread out fan-fashion behind. Neither mackerels nor perch nor any of their near allies ever have more than five soft rays in the ventral fins, and the persistence of this number throughout the Percomorphi, Squamipinnes, Pharyngognathi, and spiny fishes generally must be attributed to inheritance from the primitive perch-like or mackerel-like forms. In almost all the groups to be considered in this work, after the Berycoidea the ventral rays are I, 5, or else fewer through degeneration, never more. In the central or primitive members of most of these groups there are twenty-four vertebræ, the number increased in certain forms, probably through repetitive degeneration.

The True Mackerels: Scombridæ.—We may first consider the great central family of Scombridæ, or true mackerels, distinguished among related families by their swift forms, smooth scales, metallic coloration, and technically by the presence of a number of detached finlets behind the dorsal and anal fins. The cut of the mouth is peculiar, the spines in the fins are feeble, the muscular system is extremely strong, the flesh oily, and the air-bladder reduced in size or altogether wanting. As in most swift-swimming fishes and fishes of pelagic habit, the vertebræ are numerous and relatively small, an arrangement which promotes flexibility of body. It is not likely that this group is the most primitive of the scombroid fishes. In some respects the Stromateidæ stand nearer the primitive stock. The true mackerels, however, furnish the most convenient point of departure in reviewing the great group.

In the genus of true mackerels, Scomber, the dorsal fins are well separated, the first being rather short, and the scales of the shoulders are not modified to form a corselet. There are numerous species, two of them of general interest. The common mackerel, Scomber scombrus, is one of the best known of food-fishes. It is probably confined to the Atlantic, where on both shores it runs in vast schools, the movements varying greatly from season to season, the preference being for cool waters. The female mackerel produces about 500,000 eggs each year, according to Professor Goode. These are very minute and each is provided with an oil-globule, which causes it to float on the surface. About 400,000 barrels of mackerel are salted yearly by the mackerel fleet of Massachusetts. Single schools of mackerel, estimated to contain a million barrels, have been recorded. Captain Harding describes such a school as "a windrow of fish half a mile wide and twenty miles long."