SPAWNING SEASONS OF FISHES PROPAGATED, CHARACTER 

 OF FISH EGGS, PERIOD OF INCUBATION, ETC. 



In the following table there are presented, in a form convenient for 

 reference, some of the more important facts connected with eggs of the 

 fishes artificially cultivated in the United States. It should be under- 

 Stood that there is considerable variation in many of the items, depend- 

 ing on climatic conditions, size and age of fish, etc. ; the information for 

 such can therefore be only approximately correct. For certain of the 

 less important fishes, it is possible, from the data available, to supply 

 only a part of the information indicated by the column headings. The 

 spawning season given is generally that of wild fish in the regions where 

 fish-cultural work is prosecuted; this varies much with latitude and 

 local conditions. 



Fish eggs, as regards their i)hysical characters, naturally fall into 

 four classes, as follows : 



(1) Buoyant or floating, as the eggs of the cod, mackerel, and most 

 pelagic fishes, which come to the surface when first deposited and 

 remain there during at least the early stages of incubation. 



(2) Semi-buoyant, as the eggs of the shad and whitefish, whose spe- 

 cific gravity is but slightly greater than that of water. 



(3) Heavy, non-adhesive, as the eggs of salmon and trout. 



(4) Heavy, adhesive or glutinous, as the eggs of the flatfish, sea her- 

 ring, yellow perch, and most pond fishes. 



The differences in the types of hatching apj)aratus depend primarily 

 on the foregoing characters of the eggs. 



At the hatching stations the size of eggs is determined by placing a 

 number of moist eggs, shortly after taking, on a flat surface, side by 

 side, and noting how many are required to cover a linear inch. Owing 

 to capillary attraction between adjoining eggs leading to compression 

 or flattening of the contiguous sides, this method is liable to slight 

 error, the extent of which is in inverse proportion to the size of the 

 eggs. 



By means of the microscope, accurate measurements of small eggs may 

 be made. The size of eggs of a given species often varies considerably, 

 sometimes amounting to 25 per cent. 



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