SEA-FISHERIES LABORATORY. 343 



APPENDIX— ECONOMIC. 

 A. — Life-History and Habits. 



Spawning. — About the beginning of the year the 

 reproductive organs of mature Plaice become ripe and 

 spawning commences. Spawning — that is the complete 

 extrusion of the contained ripe ova and spermatozoa, lasts 

 over a considerable period on any one fishing ground. 

 This is due to the fact that it requires some time for any 

 one fish to extrude all its ova, and also to the considerable 

 variation in the time of ripening of the reproductive 

 organs among all the mature fish present on the spawning 

 ground. The duration of this " spawning season " varies 

 in the seas round the British Islands. In the Danish seas 

 it begins in November, attains a maximum in January 

 and February, and ends in April. In the North Sea on 

 the Scottish side it lasts from the middle of January till 

 the end of May, with the maximum at the beginning of 

 March. In Loch Fyne in the Firth of Clyde in 1898 no 

 Plaice eggs were found till the middle of February and 

 none after June ; the maximum number was found in 

 April. In the Irish Sea the exact limits of the season 

 have not been determined, but certainly it begins later 

 than in the North Sea. The maximum period as deter- 

 mined by the abundance of ripe female fish is at the end 

 of March. 



From one quarter to half a million eggs are extruded 

 by a single female Plaice during its spawning season, the 

 average number on the various fishing grounds being 

 about 300,000. This number of eggs is small when com- 

 pared with that of many other flat and round fishes. 

 Generally the larger the fish the greater the number of 

 eggs yielded. It is evident that during the spawning 



