of the Fishery Board for Scotland. 



147 



V. — THE INFLUENCE OF TEMPERATURE ON THE DE- 

 VELOPMENT OF THE EGGS OF FISHES. By Harald 

 Dannevig. (Plate I.) 



During the last ten or twelve years the development of a large number of 

 species of sea-fishes has been studied by several naturalists, as Prof. 

 M'Intosh, at the Marine Laboratory of St Andrews, Mr J. T. Cunningham, 

 at Plymouth, and others, and full and detailed accounts have been given 

 in several papers. The embryology of our common sea-fishes is therefore 

 now comparatively well-known. 



In different papers, but especially in his and Professor Prince's 

 ' Researches/ Prof. M'Intosh describes the development of the eggs of no 

 less than forty species,* and Mr Cunningham has also published 

 valuable papers on the development of several species. But in few 

 papers are particular statements given regarding the duration of incuba- 

 tion, or how long the different kinds of fish-eggs take to develop, when 

 exposed to various temperatures. It is, however, known that a high 

 temperature increases the rate of development, and that a low temperature 

 prolongs it. Prof. M'Intosh has shown that the eggs of the flounder 

 may survive after being in water heated to 98° F.;f but the precise 

 effect the difference of a certain number of degrees will have on 

 the time of incubation, and whether this effect is the same in a 

 high temperature as in a low, are questions still left to be deter- 

 mined, and the object of this paper is to give some information 

 on this subject. But I must at once mention that this work, though 

 of so great interest, has had to be put aside occasionally in order not to 

 interfere with my main duties in connection with the hatchery. My 

 statements, therefore, will not always be so full as might be desired. 



The intention being to observe the rate of development when the eggs 

 were exposed to a certain temperature, my first task was to make such 

 arrangements that the temperature of the water could be kept constant 

 and independent of the variations of the temperature of the air. 



Glass jars, holding fully 2 litres (nearly half a gallon), were filled with 

 water up to about three-fourths of their height, so that they would still 

 float when immersed in a larger bulk of water, the surface inside the 

 jar being some inches below the surface outside it. 



The separate spaces in one of the wooden hatching boxes were 

 filled with water, sufficiently deep to allow the jars to float when placed 

 in them, one jar in each space. The temperature of the water in the 

 spaces being kept at a certain point, the eggs in the jars were also 

 constantly exposed to the same temperature. 



The temperatures below zero were kept constant by freezing-mixtures ; 

 those above zero and up to the temperature of the air were controlled 

 by ice alone, while the highest were maintained constant by the addition 

 of hot water. Wood being a bad conductor, changes in the temperature 

 in all the spaces would be owing to the influence of the air ; but this of 

 course only affected the surface of the water, and the latter also being a 

 bad conductor, the contents of the jars, which were placed several inches 

 below the surface, were kept uniformly at the same temperature. 



When regularly attended to, I found this arrangement to be the 

 most convenient without going to any particular expense, and as the 

 temperatures were controlled and corrected, generally once an hour 



* Trans. Roy. Soc. Edin., XXV. iii., 1890. 



+ Report of Trawling Commission, p. 363, 1885. 



