The eggs of fishes vary much in size and form. In those sharks and rays which lay eggs the ova are deposited in a horny egg-caseon color and texture suggesting the kelp in which they are laid. The eggs of the bull-headsharlcs (Heterodontus) are spirally twisted, those of the cat-sharks (Scylliorhinide) quadrate, with long filaments at the angles. Those of rays are wheelbarrow-shaped, with four handles. One egg-case may sometimes contain several eggs, and develop several young. The ems of lance lets are small, but those of hagfishes and lam preys are large, ovate, with fibres at each end, with a triple hook at tip. The chimaeras have also large egg-cases, oblong in form.
In the higher fishes the eggs are spherical, large or small according to the species, and varying in the firmness of their outer walls. MI contain food-yolk from which the embryo in its earlier stages is fed. The eggs of the eel (Anguilla) are microscopic. According to Gunther, 25,000 eggs have been counted in the herring, 155,000 in the lumpfish, 3,500,000 in the halibut, 7,635,200 in the sturgeon and 9,344,000 in the cod. Smaller numbers are found in species with large ova. Where an oviduct is present, the eggs are of ten poured out in glutin ous masses, as in the bass. When, as in the salmon, there is no oviduct, the eggs lie separate and do not cohere together. It is only with the latter class of fishes, those in which the eggs remain distinct, that artificial impregnation and hatching are practicable. In this regard, the adaptability of the salmon and trout is pre eminent. In some fishes the ovary of but one side is developed.
In most fishes the parents take no care of their eggs or young. In a catfish (Buno cephalus) the eggs adhere to the under surface of the females. In a kind of pipefish (Sole nostomus) a large pouch for retention of the eggs is formed on the belly of the female. In the sea-horses and pipefishes a pouch is formed in the skin, usually underneath the tail of the males. Into this the eggs are thrust, and here the young fishes hatch out, remaining until large enough to take care of themselves.
In certain sea catfishes the male carries the eggs in his mouth, thus protecting them from the attacks of the female. In numerous cases the male constructs a rough nest, which he de fends against all intruders, against the female as well as against outside enemies. The nest building habit is especially developed in the sticklebacks (Gasterosteide), a group in which the male fish, though a pigmy in size, is very fierce in disposition. In a minnow of Europe
(Rhodeus amarus) the female is said to deposit her eggs within the shells of river mussels.
In the relatively few cases in which the sexes are unlike, the male is usually the brighter in color and with more highly developed fins. Blue, red, black and silvery white pigment are especially characteristic of the male, the olivaceous and mottled coloration of the female. Sometimes the male has a larger mouth, or better developed crests, barbels or other ap pendages. In some species the pattern of coloration in the two sexes is essentially different.
In various species the male develops peculiar structures not found in the female, and often without any visible purpose. In the chimaera, apeculiar cartilaginous hook, armed with teet at the tip, is developed in the male only. In t e skates or true rays (Raja) the pectoral fin has near its edge two rows of stout incurved spines. These the female lacks.
In the breeding season the male sometimes becomes much brighter by the accumulation of bright red or blue pigment or of black or white pigment-cells. This is especially true in the minnows, darters, and other fresh-water species which spawn in the brooks of northern regions in the spring. In the minnows and suckers horny excrescences are also developed on head.
body or fins, to be lost after the deposition of the spawn.
In the salmon, especially those of the Pacific, the adult male becomes greatly distorted in the spawning season, the jaws and teeth being greatly elongated, and hooked or twisted so that the fish cannot shut its mouth. After the act of spawning, all the individuals of these species die, both male and female. The Atlantic salmon and the trout show also some elonga tion of the jaws, but not to the same extent, and in these species the individuals mostly sur vive the act of spawning.
In fishes generally the eggs are laid in the spring, to be hatched in warming water. Among the salmon, trout and cod-fishes, a reverse con dition obtains. The eggs are laid in fall or winter, being deposited in water which is grow ing colder, hatching when the temperature of 54 F. is passed. In those fishes which pair, the relation seems not to be permanent, nor is any thing to be called affection recorded among them.