MANUAL OF FISH -CULTURE 205 



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by means of a siphon in the other compartment, running through a hole 

 several inches below the top of the trough. The trough fills with water 

 up to a level with the hole, when the siphon begins to act and takes off 

 the water more rapidly than it enters, to a level with the inner end of 

 the siphon, the fall being 4 to 5 inches. Air then enters the siphon, 

 and it ceases to act until the water hjrs again risen to the height of the 

 discharge hole. The water thus rises and falls in the jars automatically, 

 the interval between the successive discharges being regulated by the 

 length of the inner arm of the siphon, the size of the tube, and amount 

 of water supplied. 



After the eggs are introduced into the jars a piece of cheese-cloth or 

 linen scrim is placed over the top, and fastened by means of rubber 

 bands. The jar is then inverted and placed on the wooden supports 

 provided for the purpose, and the plug in the bottom removed to allow 

 the escape of the air and the rise and fall of water. The number of 

 eggs per jar is about 190,000 or 200,000. 



DEVELOPMENT OF THE EGG. 



The development of the cod egg is greatly influenced by the water 

 temperature, which fluctuates from day to day and makes it difficult to 

 state exactly when the eggs will hatch. With a high temperature the 

 advancement of the egg through the different stages proceeds rapidly 

 and can readily be ai)preciated with the unaided eye, while with a low 

 temperature the development is slow and may be greatly prolonged 

 by very cold water. With a mean temperature of 47° cod eggs begin 

 to hatch in 11 days, although 2 or 3 additional days are usually nec- 

 essary for all the eggs of a given lot to hatch. At 43° the time is 14 

 or 15 days, and at 38° it is 20 to 23 days. The best results are obtained 

 when the temperature ranges from 41° to 47°. The hatching proceeds 

 satisfactorily with the water at 38°, but with a lower temperature 

 t^e incubation period is so long that the fry are very weak. On the 

 natural spawning-grounds the water seldom gets below 38°, while at 

 the stations after January 1 the water used for hatching rarely gets 

 as warm as 37°, and often is as low as 31°; from the middle of January 

 to the latter part of February it remains at about 32°. Since it is 

 impossible to do even fair work when the water gets below 35°, it has 

 been the practice to warm the water by passing it through a coil of i)ipe 

 contained in a tank of warm water or by introducing steam directly 

 into the water pipe whenever the hatchery water gets below 37°. 



The water being at 47°, during the first 4 days the egg passes 

 through the different stages of segmentation 5 at the end of that time 

 tlie germinal area begins to assume the general form of a fish; and by 

 the ninth day the fish is quite well formed, and may be readily seen 

 with the naked eye. By the tenth day the embryo shows signs of life, 

 and under the microscope the heart may be seen to beat. 



