100 Spawning and Development, Sprats and Herrings. 



In this particular catch the relative proportions of outside 

 forms to whitebait proper stood as 3 to the 1,000, or only a 

 third of 1 per cent. But analysis of Ser. I. VI. denotes more. 

 From them something can be learned of the conjectural dates 

 of spawning, probable ages of the fish, and their more marked 

 developmental changes. 



Kuppfer, Meyer, and Ehrenbaum have respectively devoted 

 attention to the incubation and development of the herring and 

 sprat, both in confinement and in their free natural conditions.* 

 Speaking generally, they show these fish grow about f of an 

 inch monthly, less or more, according to temperature, food, 

 and other circumstances. The sprat's egg hatches out within 

 a week, the herring's egg from a week to a month ; heat 

 accelerating, cold retarding the process. The newly-hatched 

 larva of the herring is just under a inch, that of the sprat 

 about | inch. At the end of the first month they have attained 

 nigh J inch in length. 



Reasoning from all these premises we derive the evidence 

 given approximately in Ser. I. VI. As we find a 1-inch example 

 on 9th February, it follows spawning must have commenced in 

 January, and the hatching, &c., in this and the other fish 

 relatively keeping pace, to have gone on continuously to the 

 later dates. Further avoiding details, we have found a regular 

 succession of brood up to the 23rd August and 2nd September, 

 when a sprinkling of larval forms 28 to 73 millims. have been 

 secured. So that there can be little doubt of there being a 

 spring and late autumn spawning of herrings within the 

 Thames estuary, as Cunningham surmised.f As to the sprat's 

 period of spawning it seems more continuous, i.e., with early 

 and later spawners the older fish at the beginning and younger 

 fish following later in the season. Altogether, probably extend- 

 ing for five or six months ; the ripening fish of Ser. VI. indica- 

 ting presence of late spawners. It is the intermingling or 



* In papers embodying their researches for 1874-76, 1892, and 1806 in Commiss. 

 TTntersuch, Deutsch meere. 



t Jour. Mar. Biol. Assoc. II. (1891-92), p. 241 and p. 330. 



