THE HERRING FAMILY. 429 



THE SPRAT. (Clupea sprattus, L.) 



One of the most remarkable features about the sprat is the 

 fact that, in spite of its very close relationship to the herring, 

 it has an egg and larva of the pelagic type in direct contrast to 

 the demersal spawn of its congener. The mature female 

 appears to carry about 5000 to 5400 eggs, more or less, a 

 very moderate amount in comparison with most fishes of the 

 same spawning-habit. 



Great numbers of eggs of this species occur in the bottom 

 tow-nets, indicating that they often take up their position at or 

 near the bottom. Confining the remark to the Forth we may 

 seek a partial explanation for this in the fact that the buoyancy 

 of pelagic eggs is dependent on the specific gravity of the egg 

 being less than that of the medium, and also that the sprat 

 appears, so far as we can be guided by the distribution of 

 captured eggs, to spawn well up the reaches of the estuaries; in 

 such a position the water must incline towards brackish. The 

 medium therefore, in such cases, being of less specific gravity, 

 and that of the egg constant, the result is that the egg fails to 

 rise in the water. The same result would occur in the case of 

 any pelagic egg, if the spawners assumed a brackish habitat, 

 as is exemplified in a remarkable manner by the eggs of the 

 shad as described in 1889 by Prof. Pouchet. They closely 

 resemble those of the pilchard though devoid of an oil-globule, 

 but as they are laid in fresh water they sink and lie separate 

 and free on or near the bed of the river. The intermediate 

 character of these eggs, between the pelagic and demersal 

 types, is very interesting ; pelagic in structure but demersal 

 in habitat, they give an insight into, at any rate, one way in 

 which a pelagic spawning-habit may be changed to a demersal 

 one. These facts all tend to show how slight a distinction 

 really exists between pelagic and demersal ova. 



In the Frith of Forth the eggs of the sprat are found 

 further inland than any others, and are more plentiful there 

 than elsewhere. Thus about the district of Inchkeith eggs 

 of the sprat are abundant, and they are comparatively rare 



