Experimental observations on the spawning behaviour of the Atlantic Salmon (Salmo salar Linn.).

Summary. 1 Observations on the spawning habits of salmon were made in an experimental tank built on the banks of a tributary of the Cheshire Dee. 2 Spawning by a female (9 lb.) and a male (5 lb.) was observed. The complete operation consisted of eight emissions made almost simultaneously by the male and female in different beds, each of which was prepared by the female. 3 Before spawning the female was seen to cut a depression (bed) in the gravel with her tail and to feel the bed with her anal fin. The male took no part in the making of the bed and was often not present on the gravel when the female was cutting. He courted the female and drove away all other fish. 4 The female did not pass out eggs while cutting the bed. 5 Just before the spawning act, the female dropped into the bed, opened her mouth, erected her fins and flexed her tail upwards. When this occurred the male joined her immediately and settled alongside, quivering, with his mouth agape. At this instant the fish spawned almost simultaneously. 6 After the spawning act, the female moved upstream of the bed, cut vigorously and covered the eggs with gravel. 7 The actual spawning act took place in about 10–15 seconds, and the eggs were completely covered about 30 seconds later. 8 Mature male parr were in constant attendance on the female, and during each act of spawning pushed excitedly under her vent. It was not definitely established that they extruded sperm. 9 Spawning took place in the experimental tank at temperatures varying from 36° to 42° F. 10 An average (number) of 780 eggs were recovered from each of seven redds made by the same female. It was estimated that this female had laid 700 eggs per lb. of body weight and the percentage fertilisation was almost 99.