TREATMENT OF EGGS. Nearly all fish-eggs are spherical in shape. The true portion, which h heavily charged with yolk, is inclosed by a mem brane varying greatly in character. This mem brane may be adhesive to any foreign object or to adjoining eggs, or it may be supplied with various modifications of filaments which cause the eggs to become entangled with each other and with foreign objects, such as weeds. These prop erties necessitate different methods in their handling during incubation. Again, eggs may be pelagic, i.e. buoyant, lighter than the water, or heavy, sinking to the bottom. Some eggs, as those of the whitefish and shad, are only slightly heavier than water, i.e. semi-buoyant.
Pelagic eggs belong to the cod, flatfish, mack erel, taulog, etc. Such eggs are incubated in a way quite different from the heavy eggs; in nature they are extruded in the water and rise to the surface, where they develop. Such eggs usually hatch in a very short time, from a few days to two or three weeks. The apparatus now used for hatching pelagic eggs is the McDonald tidal box. The water enters through the cheese cloth bottom and through a small hole atone end, the latter giving the water and eggs within the box a gentle rotary motion. By means of an automatic siphon the water is also made to rise and fall at short intervals, thus insuring a more perfect renewal of the water.
Heavy eggs, as those of the salmon and trout, are spread out on small wire-bottomed trays. These are placed in tiers in long troughs, into which the water enters at one end and by an arrange ment of partitions is made to flow from below upward through the tiers of eggs, thus bathing them, and flowing out at the opposite end of the trough. During development in these trays con stant attention is necessary to avoid too strong currents through the troughs, thereby shifting the eggs, and especially to remove the dead eggs, which are attacked by a fungus, and, if allowed to remain, will speedily contaminate the whole lot.
Semi-buoyant eggs, as those of the whitefish, arc hatched successfully in the McDonald jar. This has a rounded bottom. and the water is in troduced by a glass tube extending through the lid to near the bottom. The water entering slow ly keeps the eggs in slow motion, to prevent them from 'banking' or gathering in lumps. The water escapes through the top by a tube or a sort of spout, carrying with it the young as they emerge from the eggs.
Adhesive eggs, like those of the smelt, are first mixed with starch or 'muck,' to deprive them of their glutinous properties, after which they are handled like other heavy or semi-buoyant eggs.