FISH ACCLIMATISATION. 403. 



much better, but it had. one serious drawback, as when any of 

 the ova died they got covered with a fungous growth called 

 Byssus, which communicated itself to all the healthy ova in its 

 vicinity, thereby causing their death. The next step was to 

 place the ova on the surface of the gravel. This was found to 

 answer much better, but it had another drawback. It was 

 found that dirt, the shells of the ova when the fry hatched out, 

 dead fish, and Byssus, filled up more or less all the spaces m 

 the gravel, making it very difficult to clean out, and causing 

 serious mortality amongst the young fry. Another experiment 

 was to remove the gravel and hatch the ova on the bare bottom 

 of the trough or box. This was a further improvement, but it 

 appeared that the ova having to lie on this surface from 50 

 to 100 days, according to the temperature of the water, some of 

 them stuck there and died. The next step in advance was the 

 invention of the grille. This was first used at Huningue about 

 1840. Livingstone Stone, of the United States, adopted this 

 principle ; Farnaby then brought it to this country, and used 

 it at the Troutdale Fish Breeding Establishment, Keswick, 

 Cumberland, and it has also been adopted by others in Scot- 

 land, though it has some very serious defects. The first is the 

 loss of space taken up by the frame which the glass bars rest 

 in ; the next is that dirt accumulates under the grille whilst 

 the ova are hatching, so that when the fry burst the envelopes, 

 and drop through the bars, everything goes with them. The 

 consequence of this is that the space under the grille is filled 

 with living and dead fish, the envelopes that came off the eggs, 

 and the dirt that has accumulated during the hatching process. 

 Another fault is the loss of a number of fry by getting under 

 the frame of the grille. Of course all the ova do not hatch 

 at the same time, so those that hatch first drop down through 

 the bars of the grille to get out of the dirt and hide themselves ; 

 they get under the pieces of wood that form the sides and ends 

 of the grille. Those that get in there first are all right for a 

 time, but soon others keep hatching out and force themselves 

 into this space behind the others, and so smother those farthest 



