310 BRITISH FISHERIES 



into the hatching-boxes, and applying a factor 

 obtained by experiment for each kind of egg used, 

 the total number incubated is ascertained. About 

 two or three days after the beginning of incuba- 

 tion, a certain proportion (roughly, 10 per cent) of 

 the eggs die and sink to the bottom. These are 

 removed by allowing the floating living eggs 

 to run off with the current. The quantity of 

 dead eggs is measured, and the numbers ascer- 

 tained by calculation. Then the proportion of 

 living eggs, and, consequently, the mortality, are 

 obtained. At the end of a variable incubation 

 period, depending (i) on the species of egg dealt 

 with, and (2) on the average temperature of the 

 water in the boxes during the incubation period, 

 the embryos hatch out. 



Now, so far the work has not been difficult. 

 There are many things which are trying to the 

 fish-culturist, of course ; but, compared with most 

 ordinary industrial processes, the operations of sea- 

 fish hatching are simple, easy, and straightforward. 

 But when the embryos have hatched out the 

 really difficult part of the work begins. If sea-fish 

 culture on a large scale is ever to be successful, 

 then it must be emphasised that the rearing of the 

 embryos through the period of the metamorphosis 

 is most essential. In most hatching establishments 

 this rearing is attempted, but in all cases with very 

 doubtful success. The embryos are retained in 

 the hatching-boxes for a time which is, roughly 



