82 riSH CULTURE. 



The ova teing deposited, the embryo within 

 proceeds towards development with greater or less 

 rapidity, according as the temperature of the water 

 is high or low. The higher the temperature the 

 more rapid the development. Salmon ova wiU take 

 from forty or fifty days to 120 or 130 days ; trout 

 .from thirty to eighty or ninety; greyling from 

 twelve or fifteen to thirty; charr ahout the same, 

 or rather less than trout ; other fish, as pike, perch, 

 &c., a shorter time, but temperature more or less 

 affects them aU. I have known ova deposited at 

 the same time to hatch out in the lowest trays of a 

 series of trays several days before those in the top 

 trays; the water in the lower having been exposed 

 to a warmer temperature, and being some 2° higher 

 than the water in the topmost trays. 



The ova of trout varies more in colour and size 

 than that of any other fish. I have seen some of 

 a deep salmon colour, and those of the next fish 

 would perhaps be of a pale hue, almost white. A 

 curious change takes place in the ova of greyling 

 within a few hours of its taking; when it first 

 comes forth it is of small size, not larger than a 

 No. 7 shot ; after a time a sort of false skin appears 

 to swell round it, no doubt to protect the egg, which 

 is then doubled in size. I. will describe the develop-. 



