of the Fishery Board for SeotlancL 



403 



Captain Damievig has been so successful in his operations for the 

 artificial hatching of sea fish that it is worth while giving an account 

 of the exact method adopted. When the cod are ripe so much milt 

 is introduced into a small tub containing a few pints of sea water (sp. 

 (jr. 1-024) as to render the contents slightly milky. The spawn of 

 the ripe females is then allowed to run into the tub, the water being 

 occasionally stirred by the hand. The fish examined or used are 

 transferred to another tank, and the process is repeated every two or three 

 days for a couple of months. The next step is to stir the impregnated 

 spawn in fresh sea water to get rid of the excess of milt, after which it is 

 poured into a glass receiver, 18 inches high, half full of clear sea water. 

 In a few minutes the serviceable spawn separates to form a compact layer 

 near the surface, while dead ova and impurities sink to the bottom. With 

 a perforated ladle the living spawn is removed and placed in a smaller 

 glass used as a measure, which, by careful counting and weighing of 

 the ova, has been found to contain G0,000 eggs. From the measure the 

 spawn is poured directly into the hatching apparatus. These are 8 feet 

 long, 2 feet wide and contain each 10 small boxes, able collectively to 

 accommodate 3,000,000 eggs, i.e., 300,000 in each box. The spawn 

 lies in these boxes, through which a steady current flows, for two or three 

 days, when it is removed to allow the apparatus to be cleaned ; and 

 after a fresh sorting and separation of the living from the dead as before, 

 the living ova are returned to the apparatus. This process is repeated 

 every two or three days until the spawn is ripe ; live spawn is perfectly 

 translucent, dead spawn is light grey in colour and opaque. A few days 

 before the embryo is ready to burst its shell, the apparatus and spawn are 

 cleansed for the last time, and note is made of the quantity of spawn 

 remaining. 



The loss may vary between 20 and 70 per cent., and depends chiefly 

 upon the degree of saltness of the water during the hatching, which varies 

 from time to time according to the prevailing wind, and the presence of 

 Baltic currents. 



Captain Dannevig then discusses the influence of salinity generally, and 

 the position of the micropyle in fish ova. He shows that the specific 

 gravity of ripe cod spawn being 1,022, that of sea water 1,025 and that 

 of fresh water 1000, if cod spawn is blown or carried to the mouth of 

 an estuary, when the specific gravity of the surface water is reduced by 

 admixture with fresh water, the ova will sink until they reach a layer 

 of specific gravity sufficient to keep them in equipoise, and thus pass 

 under the fresh water altogether. 



The lobster fry thrive in salt water, but immediately die on being 

 transferred to fresh water. While the milt of the male salmon is shed on 

 the ova over which the male swims, in the case of the cod the male fish 

 swims underneath the female, the difference in either being due to the 

 presence of the micropyle on the upper or lower surface respectively. In 

 the hatchery the facts which nature teaches are made use of, and water is 

 only pumped from the sea to the large pond or reservoir on those days 

 when the sea is sufficiently salt to float the fish-eggs, and in the intervals 

 when the salinity of the sea is not high enough, the water which has 

 already passed through the apparatus is again made use of by being 

 repumped into the pond. The aeration of the water in the pond is 

 ensured by the indraught of the pumped water carrying with it air from 

 holes bored in the suction pipe. 



The difficulty of getting water of a sufficiently high temperature is 

 obviated by heating the pond water by the waste steam, and if 



