59 



THE SPAWNING OF THE PLAICE. 



By B. STORROW. 



Ill the report of last year appeared a short account of the 

 spawning of the cod, the marked periodicity of which was noted. 

 A similar periodicity, although rendered obscure by the number 

 of fish in the tank, was also mentioned in connexion with the 

 spawning of the plaice. 



In order to obtain some evidence of this, a male and female 

 plaice of ■^'' and 35 cm. respectively, and two males of 32 and 34 

 cm. and one female of 42 cm., were isolated on the 15th 

 February, and observations were made from day to day as to the 

 spawning of the isolated females. A record was also kept of 

 the spawning of the plaice not isolated. 



In the case where one male and one female were together the 

 first eggs appeared on the 10th February and were not fertilised, 

 as were also the next lot which was spawned on the 25th. 

 Further spawning took place in March on the 5th, 8th, 20th and 

 the 26th, but many of the eggs were not fertilised. 



The female of 42 cm. spawned on the 17th, 22nd and the 

 28th of April, and on the 5th of May but no eggs were fertilised. 



It is probable from few of the eggs being fertilised in the 

 first case of isolation and none in the second that the males were 

 not suitable, and that this would have some effect on the 

 periodicity of the spawning of the female. 



From the tank containing the other plaice, some 32 in 

 number, first day eggs were obtained in February on the 24th, 

 27th and 29th ; in March on every day with the exception of the 

 3rd, 5th, 10th and the 15th ; in April on every day up to the 

 11th and afterwards on the 14th, 15th, 16th, 18th, 20th and the 

 22nd. In May newly spawned eggs were taken on the 6th and 

 the 12th, but those of the latter date were not fertilised. 



The average diameter of the eggs was 1"73 mm.| 



♦ Unfortunately tlie male was replaced in the plaice tank before measuring. It was 

 smaller than the female. 



tin the Report of last j-ear p. 2i, line 4, 1-28 cm. should read 1'28 mm. 



