Page:The American Cyclopædia (1879) Volume VII.djvu/227

FISH CULTURE 219 low the surface of the water, the bars being near enough together to hold the eggs, while dirt and the young fish when hatched fall between them and are removed through an aperture in the bottom of the tray. These trays are placed in shallow vessels or cis- terns, each cistern containing several of them. Another French apparatus is a series of troughs arranged one a little above the other like steps, the water entering from a small jet at one end of the upper trough and pass- ing out at the other, traversing each trough in succession. A box, about 2 ft. long, 18 in. wide, and 6 in. deep, which may be fastened in the raceway and allowed to float in the cur- rent, or placed in a spring, is also used for hatching. The bottom may be of board strewn with gravel to receive the eggs, holes being bored in each end below the water line for the passage of the current; or it may be com- posed of fine wire gauze, which should be painted. When the trout enter the raceways and begin to make their nests, preparation should be made to obtain their spawn. The fish are taken from the water, and the milt of the male and spawn of the female are expressed into a pan holding about six quarts, and not more than a quarter full of clear water. If the milt is expressed into the water, and the eggs are afterward added, the process of impregna- tion will be facilitated. The fish are held as near the surface of the water as possible while the hand is passed gently along the abdomen, the spawn and milt dropping into the pan be- low. By this method about 65 per cent, of the eggs are fecundated. After the eggs have re- mained in the water 20 minutes or half an hour, they should be carefully washed, when they are ready to be placed in the hatching trough. Another process, however, said to have been the discovery of Mr. Vrasski, a Russian, known as dry impregnation, has been introduced into this country within a year or two by Mr. George Shepard Page of New York. By this process, which consists in expressing the ova into a dry pan and bringing them in contact with the milt before the addition of water, an average of 96 per cent, is fecundated. This method has been extensively adopted by Amer- ican fish culturists. During the process of hatch- ing, the troughs should be examined with care, and any addled eggs, accumulation of sediment, or growth of fungus removed. The period of incubation varies with the temperature. At 37 it is 165 days; at 39, 121 ; at 41, 103; at 44, 81 ; at 48, 56 ; at 50, 47 ; at 52, 38 ; and at 54, 32. When the trout are first hatched they have an umbilical sac, about three times the size of the body, which furnishes them sustenance for a period varying, with the temperature of the water in which they are hatched, from 77 days at 38 to 60 at 40|, 46 at 43f , and 30 at 50. When the sac is absorbed they require food, which may consist of bonnyclabber, curd, fresh shad or herring roe, raw or boiled, the yolks of eggs boiled hard, coagulated blood, liver raw or boiled, &c., which should be grated or pulverized. When they outgrow the hatching troughs, they are let into the nurseries, and should be furnished with sunlight. For the adult trout similar food will suffice, maggots bred in de- caying meat being perhaps the most nutritious. One great advantage of artificial breeding con- sists in the large proportion of eggs and fry that are saved from destruction. In the natu- ral state these are the prey of frogs, aquatic birds, various species of fish, and numerous water insects. Fecundated ova, after the first formation of the fish is seen, may be trans- ported without injury, if packed in moist moss in glass jars or tin boxes admitting the air. At a temperature from 5 to 15 above freezing point, they may be kept packed for two weeks; and even after the lapse of six weeks they have been found uninjured. The fry and adult fish may be transported in bar- rels or smaller vessels, care being taken to change the water and have it properly oxygen- ated. The spawn of salmon requires a some- what longer period of incubation than that of trout in water of the same temperature. In Scotland from 100 to 130 days are occupied, while in spring water of a uniform tempera- ture of 50 not more than 50 or 60 days would probably be required. In the Canadian estab- lishments, with river water of from 33 to 34, the period is 170 to 180 days. The fry, as in the case of the trout, are provided with an umbilical sac, which they carry for about six weeks, after which they require food similar to that of the trout. In Scotland the fry are generally kept in ponds and artificially fed un- til they become smolts, when they are turned into the river. This system has been criti- cised by Mr. Buckland and others, who con- tend that better results will follow if the fry are turned into the stream as soon as the sac is absorbed. The same conclusion has been reached with respect to trout by the marquis de Folleville at his establishment near Rouen. A pond an acre in extent, with an average depth of 4 ft., has been found large enough for the nurture of 300,000 young salmon. Salmon ova have been kept in ice for 90 days, half of the frozen eggs being afterward hatched ; and they have been transported from England to Aus- tralia, packed in moss and surrounded with ice, occupying about 80 days in the passage. A portion of them were found to be sound upon arrival, and were subsequently hatched in Tas- mania. But whether the attempt to stock the rivers of Australia with salmon has succeeded, remains to be determined. The spawn of shad is hatched in 72 hours in water at a tempera- ture of 78, and in seven days when the tem- perature is 60. The umbilical sac sustains the fry only about six days. The most successful hatching apparatus is a box patented by Seth Green with a bottom of wire gauze, sustained in the water by two float bars fastened to the sides at an angle with the top. This is an-