of the Fishery Board for Scotland. 171 



also by affecting the rapidity of digestion. In very cold water the fishes 

 give up feeding altogether, because the ferments upon which digestion 

 depends do not act, or act very slowly, at low temperatures, and in fishes, 

 as in other animals, appetite waits on digestion, and this is, on the other 

 hand, correlated with the metabolism in the tissues. It has been shown by 

 Krukenberg that tlie pepsine or analagous body in the stomach of fish 

 acts as well at 20 C. as at 40 C, at which, among mammals, digestion is 

 most active, and that the rapidity of its action is closely related to the 

 temperature ; and Knauthe and Zuntz have shown that the same thing 

 applies to the metabolism in fish, the vital activities being more active in 

 the higher temperature, as shown by the excretion of carbonic acid gas 

 and other products of metabolism. 



5. The Sprat (Clupea siyrattus). 



Comparatively few observations have been made on the rate of growth 

 of the sprat. Cunningham appears to have been the first to publish a 

 definite statement ou the subject,* making use of a number of observations 

 of Ewart and Matthews, contained in a paper ou the nature of Thames 

 and Forth whitebait, which appeared in the Fourth Annual Report of the 

 Fishery Board for Scotland. t In that paper an account was given of the 

 proportion of herrings and sprats, and their sizes, in collections obtained 

 at different times of the year from February to August, and from a study 

 of these Cunningham came to the conclusion that the little sprats two to 

 three inches long obtained in February, March, April, and May were 

 about one year old. The new brood of the year began to appear in the 

 whitebait in June and increased to August, when they measured from 

 1 inch to 1^ inch (25-38mm.), The proportion of sprats in the samples 

 in this month was 48 per cent., but the number of the small soaleless 

 sprats gradually increased during the month until 90 per cent, consisted 

 of these. Of 2600 specimens of whitebait procured in samples of about 

 two hundred each during December, January, and February in the Firth 

 of Forth, over 99| per cent, were sprats measuring from If inches to 

 2| inches (35 to 70mm.). In the samples from the Thames the average 

 size was 2 inches (50mm) in April, and 2| inches in May. 



From the examination of the otoliths of a considerable number of sprats, 

 partly from the North Sea and partly from the Baltic, Jenkins came to the 

 conclusion that the growth was somewhat more rapid. He assigns a 

 length of 75mm. (3 inches) to the sprat one year old; of 110mm. 

 (4| inches) to the sprat which has completed two years, and of 130mm. 

 (5i inches) to the sprat three years old.J 



The investigations made by myself on the rate of growth of the sprat, and 

 described in this paper, were on material collected almost entirely in the 

 course of the trawling investigations in the Moray Firth and Aberdeen Bay 

 by means of a small-meshed net placed outside the cod-end of the trawl 

 net ; but some of them were obtained by the shrimp-net and tow-nets. The 

 fact has to be kept in mind, because apart from the difference in vertical 

 distribution at different stages, which might result in sprats of different 

 size being taken in the bottom or surface net at the same time, the size 

 of the mesh exerts an important influence on the sizes of the samples 

 taken, at least as far as the smaller specimens are concerned, and there is 

 no doubt that in several of my collections the very small slender sprats 



* Journ. Marine Biol. Assoc. II. p. 241, 1892; "Marketable Marine Fishes," p. 167. 



tP..98, 1886. 



% Wissetisch. Meeresuntersuch. Kiel N.F. Bd. 6 Abtheilwiff, Kiel, p. Ill, 1902. 



1 



