In the lagoons of the Adriatic and the salt marshes of various parts of France examples of the cultivation of salt-water fish are to be found analogous to the pond culture of fresh waters. Here, as in ancient Greece and Rome, it is the practice to admit young fish from the sea by sluices, into artificial enclosures or "viviers" and to keep them there until they are large enough to be used. An interesting modification of this method of cultivation has been introduced into Denmark. The entrances to the inner lagoons of the Limfjord are naturally blocked against the immi gration of flatfish by dense growths of sea-grass (Zostera) although the outer lagoons are annually invaded by large numbers of small plaice from the North sea. The fishermen of the district consequently combined to defray the expenses of transplanting large numbers of small plaice from the outer waters to the inner lagoons, where they were found to thrive far better than in their natural habitat. The explanation has been shown by Dr. Petersen to be due to the abundance of food, coupled with the lack of overcrowding of the small fish. This transplantation of small plaice in Denmark has been annually repeated for many years with the most successful results and a suitable subvention to the cost is now an annual charge upon the Government funds.
As a result of the international North sea fishery investigations, it has been proposed to apply the same principle for the develop ment of the deep-sea fishery in the neighbourhood of the Dogger Bank. Experiments with labelled plaice, carried out in i904 by the Marine Biological Association, showed that small plaice trans planted to the Dogger Bank in spring grew three or four times as rapidly as those on the inshore grounds, and the same result, with insignificant variations, has been obtained by similar experi ments in later years. (See Reports of the Ministry of Agriculture and Fisheries cited at the end.) In this case the deep water round the Dogger Bank acts as a barrier to the emigration of the small plaice from the shores. It has consequently been proposed that the small plaice should be transported in millions to the bank by well vessels every spring. It is claimed, as further result of the experiments, that from May to October the young fish would be practically free on the shallow part of the bank from the risk of premature capture by trawlers, and that the increased value of the fish, consequent upon their phenomenal growth rate, would greatly exceed the cost of transplantation. The development of seining on the Dogger Bank since 1919 has probably increased the risk of premature capture, but satisfactory information on this point is lacking. In the experiments made by the English Min
istry of Fisheries the transplanted fish retaken by seiners amounted to about 20% of the total recaptured in 1922 and 1923, but the actual months are not stated.
Not unlike the work on plaice is the rescue work carried on in the United States, chiefly by the Bureau of Fisheries, but also by the States of Minnesota, Wisconsin, Iowa and Illinois. With the recession of the waters of the Mississippi river after spring freshets, many fishes become land-locked in temporary ponds or sloughs. By removing them to permanent waters they are saved from death due to drying of the ponds. In 1926 the Bureau of Fisheries seined about 1 so,000,000 impounded fish and returned them to open waters and similar work is undertaken each year.
In France and Japan the methods of oyster and mussel culture are similar in principle to those just described. A breeding stock is maintained to supply the ground or the "collectors" with spat, and the latter, when sufficiently grown, is then transplanted to the most favourable feeding grounds, care being taken to avoid the local overcrowding which is so commonly observed among shell-fish under natural conditions.