MIDDLE-THIRD HATCHING-HOUSE. 121 



Sediment had much to answer for in the early days of trout- 

 culture ; all sorts of disasters were laid to its charge. If there were 

 an undue proportion of deformities, it was due to sediment ; if half 

 the eggs were lost during the incubation, it was due to sediment ; 

 if the outlet clogged, and the box ran over, it was all the fault of 

 the sediment. Now it is possible that some deformities may be 

 caused by sediment ; it is even probable it is so ; but the experi- 

 ments with young breeders have shown that improper selection 

 of the parents is a much more prolific cause, and hybridism 

 sometimes produces an entire batch of malformations. If the ova 

 lie on gravel, and sediment is allowed to collect, it will smother 

 most of the embryos, but this is supposing an extreme case. The 

 real harm results much more frequently from inconsiderate washing 

 at an early stage. Sediment sometimes may cause an overflow, but 

 only where the outlet screen is too fine, and at certain stages the 

 fry are not slow in taking advantage of the chance of escape. 



Two inches of free space between the bottom of the hatching- 

 box and the glass grille is ample provision against sediment ; a 

 little on the eggs at first, or up to the end of the first half of the 

 hatching period, does little harm ; after that time the eggs may 

 be washed with safety. In a well-arranged establishment there 

 should not be enough to discolour the eggs. But at the time of 

 which I am now writing nearly everything had to be discovered 

 that was part of the charm in fish-culture, and sediment was a 

 terrible bugbear, and had to be provided against. Flannel filters, 

 wire screens, and that dirtiest of all abominations, gravel filters, 

 were thought necessary, and the simple settling well was unthought 

 of. Sediment constituted a real danger, the more so on account of 

 the precautions taken against it. 



To prevent an overflow, No. 9 zinc was used on all the outlets, 

 and after the fry hatched a safety-screen with No. 8 was fitted 

 so soon as the grilles were taken out. This screen was 1 inch 

 lower than the sides of the box, so, even if it did clog, the fry 

 were to a large extent caught between it and the outlet screen, 

 only a few hanging themselves in the No. 9 zinc in the short 

 time elapsing till the next visit of the attendant. 



