Ichthyology of the Firth of Forth. 53 
most important characters, or place reliance on characters which do 
not exist. 
Sprats are found in the Firth of Forth throughout the whole of 
the year, and, like many small animals, appear to be very suscep- 
tible of cold. During the warm summer months, they are seen sport- 
ing about in large shoals, in every part of the Firth, occupying a 
considerable extent of water, and causing a ripple on the surface 
with their fins, while they become the principal food of many ma- 
rine birds, which assail them in the water, or prey on them from 
above. As the cold weather advances, these little fish are no long- 
er seen in the lower part of the estuary, but are found to ascend 
the Firth to a considerable distance, and to select that part of the 
river where the fresh and salt waters mingle together ; for it is a well 
known law in chemistry, that when two fluids of different densities 
come in contact, the temperature of the mixture is elevated for a 
time in proportion to the difference in density of the two fluids. Owing 
to mutual penetration and condensation, such a mixture is constant- 
ly taking place in the rivers that run into the sea, and the tem- 
perature of the mixed water is accordingly elevated. In the year 
1830, the sprat was remarkably abundant all over the British coast, 
but more particularly on the coasts of Kent and Essex, where they 
were taken in immense quantity, so that they were sold at sixpence 
a bushel as manure for the land. 
The sprat is generally considered as a delicious well-flavoured 
and wholesome fish, and is eaten in considerable quantity in this 
country, both in the fresh and salted conditions, but is very seldom 
brought to the Edinburgh market. They spawn early in the month 
of March, and feed on small crustaceous animals. 
The most common size of a sprat is from four to five inches in 
length, but it is observed occasionally to exceed six inches and a 
half, when it is named in the neighbourhood of Alloa the King of 
Garvies. 
The colour of the back is a deep glossy blue, the sides, belly, and 
gill-covers of a pure silvery white, passing into green and blue re- 
flections, when viewed in different lights ; the dorsal and caudal 
fins dusky, minutely spotted with black ; the pectoral and ventral 
fins white, slightly tinged with orange. On the crown of the head 
is a dark spot placed between the eyes, which is very perceptibly 
seen when young, but as the fish increases in size the spot gradually 
becomes obliterated. The eye is large, the diameter being not 
less than one-fourth of the whole head ; the upper and lower mar- 
gins are tinged with black. Each operculum has a slight notch placed 
on its upper and posterior edge. The teeth in the jaws are small, 
