August 1, 1895.] 



KNOWLEDGE 



189 



wooden walls, and covered in with a roofing of galvanized 

 iron. On the bottom, lying loose on the concrete, there 

 is a system — or rather two systems — of branched perforated 

 piping, of diminishing diameter, each system occupying 

 one half of the floor respectively, and connected with an 

 outflow pipe ; a contrivance to allow of the rapid drawing 

 off of the bottom layer of water, which soonest becomes 

 tainted, without unduly depressing the level of the water 

 in the pond. Somewhat above these pipes a wooden 

 platform is placed, spaces being left between the boards in 

 order to permit waste matters to slip through, when they 

 may be quickly removed in the manner indicated ; on the 

 flooring the flat fishes rest. As has been said, it is into 

 this pond that the adult fishes are put at the spawning 

 season, and they spawn naturally, as they would in the 

 sea, merely needing to be fed, and furnished with water 

 enough to preserve them in good health ; and the eggs, 

 ' rising towards the surface, are carried by the overflow into 

 a compartment known as the " spawn collector," a filter 

 or sieve that retains the eggs, while the water passes away. 



The ova are lifted out by a haircloth tray — the use of 

 bags of silk bolting-cloth is being tried — the process usually 

 occupying some hours, and are then transferred to the 

 hatching-boxes, where a constant current of pure sea- 

 water is maintained through them. 



The pre-eminent attraction of the whole establishment 

 is, of course, the Dannevig hatching apparatus. They 

 form the special feature in the Norwegian method. They 

 consist of an oblong wooden box, divided into two series 

 of seven water-tight compartments, by one central longi- 

 tudinal and six transverse partitions. With the first and 

 the last compartment in each series, those at the ends, 

 the inflow and outflow pipes communicate ; the other five 

 compartments in each series are wider, and contain the 

 hatching-boxes. With wooden sides and a bottom of 

 haircloth, the latter are attached to the top of the trans- 

 verse partition by leather hinges, and when the apparatus 

 is full of water the free end floats up. The apparatus, 

 each with its ten boxes, are arranged in pairs, four on 

 each side of the apartment. On entering an apparatus the 

 water falls into one of the narrow compartments, which 

 communicates with its fellow, and upon both becoming full 

 it overflows into the first pairof hatching-boxes, and through 

 the haircloth bottom into the compartments in which they 

 are contained ; this overflows into the second pau- of boxes, 

 and so on, until the narrow compartments at the lower end 

 are reached, whence it escapes by a waste pipe through the 

 floor. The fact of the free edge of the box being floated 

 up as the compartment becomes full of water, admits of 

 the application of a special feature of Dannevig's system — 

 the forcible depression of the box at intervals, which forces 

 water up through the haircloth bottom. As the current 

 passes in at the top it falls on the surface, but it alone is 

 insufficient to maintain the buoyant eggs in a state of 

 equal distribution throughout the mass of water, and unless 

 an up-and-down movement is imparted to the boxes the 

 eggs collect in a layer on the surface. The movement is 

 accomplished by an iron rod, jointed to the upper end of 

 the hatching apparatus, and passing down the middle 

 between the boxes, and possessed of five short, transverse 

 pieces, one for the free edges of each pair of boxes. 

 Without going into details, suffice it to say that motion is 

 conveyed to the rods, so that they are alternately slowly 

 hfted from the boxes and allowed rather suddenly to fall 

 upon them. When the rod is raised, the buoyancy of the 

 boxes causes them to float up, as has been described, and 

 when it falls it is weighted sufficiently to press them, and 

 submerge them in the water, which rises through the 

 perforated bottom. 



By and by the fishes emerge from the eggs. The fry 

 are kept in the hatching-boxes until the yolk-sac, from 

 which they derive their nourishment in the early stage, 

 is nearly absorbed, and they are able to eat ; no attempt 

 being made to feed them, they are transferred directly to 

 suitable places in relation to the fishing-grounds, where 

 they are liberated. Thus they are deposited in the sea 

 while still in their larval state. At this period, it may be 

 mentioned, the fry of flat fishes have not attained the 

 characteristic appearance of their kind, but resemble those 

 of round fishes, such as cod or haddock ; the body is 

 symmetrical, and the eyes are placed one on either side of 

 the head ; and it is only after the lapse of two months or 

 so, which are spent in the surface waters, that they acquire 

 the adult form and habits fitted for a bottom life, enabling 

 them to secure protection by resemblance to the groimd on 

 which they he, and by burrowing. There can be no doubt 

 that gi'eat destruction of the young arises from natural 

 causes during this period of pelagic life, and a great step 

 in advance would be made were they artificially protected 

 for the necessary time before planting them on the fishing- 

 grounds ; clearly, it would immensely increase the 

 usefulness of the hatchery to the fishing industry. The 

 fish at this stage are small, and multitudes could be dealt 

 with. For the purpose, control must be had of a large 

 body of water to form tidal ponds, and this lies ready to 

 hand in the sea-creeks adjoining the hatchery. If enclosed, 

 they would furnish admirable quarters for the rearing of 

 many millions of fry simultaneously, and would afford a 

 volume of pure sea-water exceeding half a million gallons. 



This inclosure would also serve for the retention of 

 large numbers of brood-fish, or spawners, which would be 

 collected gradually before the actual hatching work begins, 

 the small arm or inlet of one of the creeks which is now 

 utilized, though it is very serviceable in this respect, being 

 of insufficient size to store aU the fishes required. At the 

 hatcheries in the United States, Norway, and Newfound- 

 land, ample accommodation of this sort has been provided. 



At these hatcheries the species of food-fish almost 

 exclusively treated is the cod, which constitutes a very 

 important element in the fisheries of those countries. But 

 in Scotland the cod, though an important fish, is not the 

 most valuable, nor is there definite evidence of the supply 

 diminishing. On the contrary, it is the valuable flat-fishes, 

 soles, lemon-soles, turbot, and plaice, that show unquestion- 

 able decrease, and it was therefore decided that with these 

 fishes the hatching operations should be commenced at 

 Dunbar. 



The sixteen Dannevig apparatus there can together 

 accommodate at one time about 80,000,000 cod eggs, and 

 since, during the spawning season of any species, the 

 hatching-boxes may be refilled at least twice, no fewer 

 than about 100,000,000 cod eggs may be handled in the 

 course of one season. Plaice eggs are larger, and perhaps 

 only 100,000,000 could be hatched. The eggs of the sole 

 are about the same size as those of the cod, those of the 

 lemon-sole and turbot somewhat smaller, so that the 

 working capacity of the hatchery in the year may be 

 stated as equal to several hundred millions. About 92 

 gallons of water are requisite per hour for each apparatus, 

 that is, for about 5,000,000 cod eggs, so that the supply 

 for sixteen apparatus must be about 1500 gallons per 

 hour, and adding 800 gallons for the spawning-pond, the 

 total quantity for 80,000,000 cod eggs is 2300 gallons per 

 hour. The pumps are, however, capable of throwing over 

 7000 gallons per hour, and thus by increasing the apparatus 

 — an inexpensive proceeding compared with the cost of 

 enlarging the water supply — the quantity of spawn that 

 may be dealt with may be more than doubled. 



