In the lobster (Homarus) the eggs are carried attached to the appendages of the lower surface of the abdomen of the female and average 30,00o in lobsters 13 in. long. The larvae hatched from the eggs pass through a remarkable series of transformations at successive moults. During the first four stages they are minute and free-swimming and subject to destruction by storms and countless enemies; but at the close of the fourth stage, or in the fifth, they become ambulatory, descend to the bottom and show an ability to protect themselves. "One lobster at this stage is worth many thousands in the first" (Herrick). Owing to the hard outer shell it is not possible to "strip" the lobster and culti vation, therefore, consists in rearing the naturally-hatched young through the helpless free-swimming stages to the ambulatory bottom stage capable of self protection. The most successful method is that devised by Mead and his co-workers and first used at Wickford, R.I., under the auspices of the Rhode Island commissioners of inland fisheries.
The unit apparatus is a wooden box io ft. square and 4 ft. deep with screened openings in the bottom and on two opposite sides near the top. The boxes, in groups of six, float with tops above water, supported by rafts 75 ft. long anchored in the sea in a protected situation where the water is of suitable quality. Near the bottom of each box a horizontal two-bladed propeller, with a radius of about 44 ft., is made to revolve by means of suitable shafts and gearing driven by a naphtha motor or other power source. The propeller draws water through the screened opening in the bottom of the box and forces it upward in a spiral course to its escape through the side openings. Egg-bearing or "berried" lobsters are placed in one of the boxes just before the eggs are ready to hatch and, as hatching takes place, the fry are carried toward the top of the box and kept in suspension as though in the open sea. For rearing, the fry are transferred to other boxes where they secure natural food from the entering sea water but are also supplied abundantly with other food, pref erably chopped, cooked beef, which is kept in suspension by the current and retained in the box by the screens. During the six to eight weeks season 500,000 "fourths" may be reared in boxes. The method is believed to produce about 8o times as many fourths as are necessary to maintain the normal population of adults and heavy captures are therefore possible without depleting the grounds.
Objects and Utility of Fish-hatcheries.—The earlier advo cates of artificial propagation and fish-hatching seem to have been under the impression that the thousands of fry resulting from a single act of artificial propagation meant a corresponding increase in the numbers of edible fish when once they had been deposited in suitable waters; and also that artificial fertilization ensured a greater proportion of fertilized eggs than the natural process.
For the first proposition there is no evidence, while the second proposition is now discredited. The advantage of artificial hatch ing lies in protecting the unhatched eggs from the very large destruction to which they are subjected under natural conditions. But it is recognized that the great fertility of fishes is nature's provision to meet a high mortality—greater in sea-fishes with minute pelagic eggs—a condition which entails a greater delicacy of Unir larvae at the time of hatching. Artificially propagated eggs and fry must submit, after planting, to the same mortality as the other eggs and fry around them. Consequently it is useless to plant out eggs or fry unless in numbers sufficiently great to increase appreciably the stock of eggs and fry of the same age already existing. It is this, combined always with the suitability of the external conditions, which accounts for the success of the best-known experiments of American pisciculturists.
The shad fisheries of the streams of the east coast of the United States declined on the whole 74% from 1896 to 1923, and are now totally destroyed in many streams, in spite of plants of fry which reached the large total of 400,000,000 in 1898, but, owing to the difficulty of obtaining breeding fish, has since then, in general, declined to about 35,000,000 in 1923. We have still little knowledge of the habits and life history of the shad, of the extent and direction of its migrations. Its ascent of streams has been often impeded by dams, and pollution has doubtless adversely affected the spawning migration, vitiated the breeding grounds and destroyed the fry. Artificial hatching has failed to maintain the species in Atlantic waters under these handicaps and in the face of intensive fishing. Under more normal physical conditions and with fuller knowledge of the life history of the species it might be effective in these waters as it begins to be in the case of the Pacific salmon. The artificially propagated eggs of the shad from the eastern rivers of the United States were planted in those of California, where the species did not naturally occur. The conditions were suitable, and the species became at once acclimatized and has increased greatly. Similarly, reservoirs and streams can be stocked with various kinds of fish not pre viously present. But in the case of indigenous species the breeding stock must be very seriously reduced before the addition of the eggs or fry of a few score or hundreds of fish can appreciably increase it.