THE BREEDING SEASON 17 



Biological Association have shown that in the plaice of the 

 South Devon bays the maximum spawning period is between the 

 third week of January and the second week of February. This 

 period in the North Sea and Irish Sea would appear to be sUghtly 

 later. Herdman ^ records that, in the year 1904, the plaice in 

 the open-air ponds at the Port Erin Biological Station started 

 spawning on March 3, and those at the Peel (Lancashire) Sea 

 Fish Hatchery (under cover) on March 1. 



In the Holostean fish, Lefidosteus, which Uves in the fresh 

 waters of North America, the breeding season recurs with a 

 wonderful regularity about May. At this time the fish resort in 

 large numbers to shallower water, where the temperature is 

 higher. Here the ova and spermatozoa are emitted during 

 recurrent periods of sexual excitement.^ The related fish, Amia, 

 of Central and Southern North America, spawns usually in May, 

 the exact season depending somewhat upon the temperature of 

 the water. The fish make their way from deep water to the 

 shallow spawning place, which is generally at the end of a 

 swampy lake.^ 



In the Crossopterygian fish, Polypterus bichea, the ova ripen 

 in the summer months from June to September, the breeding 

 season depending upon the period of inundation, as in most 

 of the Nile fishes.* The other species of Polypterus (P. senegalis 

 and P. laprodei), which inhabit the river-basins of tropical 

 Africa, spawn also in the wet season in July and August.^ 



In the Dipnoan, Ceratodus, of Australia the principal time 

 for spawning is September and October, at the end of the dry 



^ Herdman, " Spawning of the Plaice," Nature, vol. Ixix., 1904. See also 

 Wallace (W.), same volume. For information concerning the spawning seasons 

 of different species of fish, 2'he Journal of the Marine Biological Association, the 

 publications of the English and Scottish Fishery Boards, and the International 

 Council for Fishery Investigation, should be consulted. These reports show 

 that the migratory and reproductive periods of fishes are affected by the 

 temperature, salinity, &c., of the sea. 



^ Agassiz, "The Development of Lepidosteus," Proc. Amer. Acad. Arts 

 and Science, vol. xiv., 1878. 



' Bashford Dean, " The Early Development of Amia," Quar. Jour. Micr. 

 Science, vol. xxxviii., 1895. 



* Harrington, " The Life-Habits of Polypterus," American Naturalist, 

 vol. xxxiii., 1899. 



' Budgett, " On the Breeding Habits of Some West African Fishes,'' 

 Trans. Zool. Soc, vol. xvi., 1901. 



B 



