MANUAL OF FISH-CULTURE. 213 



eggs. The largest number of eggs takeu from one fisli in Casco Bay 

 in 1897 was 200,000. 



From the field the fertilized eggs are conveyed to the station in jars, 

 as described in the chapter on cod propagation. For short shipments 

 they may be transported in buckets or cans. 



Mackerel eggs may be artificially incubated in a variety of ways. In 

 1896 three forms of apparatus were employed for comparative purposes. 

 These were (1) the McDonald hatching-jar, with the water supplied 

 through the long central tube and discharged through a cheese-cloth 

 top; (2) the Chester jar, and (3) the automatic tidal-box; the latter 

 gave the best results. 



Owing to the very small size x)f the eggs, from 200,000 to 225,000 

 may be placed in a Chester jar and 450,000 or more in a tidal box 20 

 by 11 inches. The eggs are manipulated in about the same way that 

 cod eggs are, but, owing to the short period of incubation, require very 

 little handling. 



For reasons not yet definitely determined, but apparently connected 

 with the condition of the eggs rather than the methods of hatching, 

 mackerel ova are liable to exceedingly large mortality during incuba- 

 tion. While as many as 75 per cent of certain small lots of eggs have 

 produced fry, less than 1 per cent of most of the eggs hatch. 



The period of incubation at a mean water-temperature of 58° is about 

 5 days. In 48 hours after impregnation the embryo is discernible, and 

 in 08 hours its development is far advanced. The critical period seems 

 to be the end of the third day, when a large part of the eggs die. 



The fry are planted within 24 hours of hatching. They are taken 

 to the natural spawning grounds in regular transportation cans and 

 liberated below the surface of the water. 



