of the Fishery Board for Scotland. 181 
‘no sea fish has been found to attain the mature condition in the first 
year of its life, ov before the close of its second year. Some spawn for the 
first time at the end of their second year, 7.e., when two complete years 
of age. These, as a rule, are the smaller species, as the sprat, the armed 
bullhead, the Norway pout, and the lesser weever ; but this class includes 
also the whiting, which reaches maturity with comparative rapidity. 
Among those which spawn for the first time at the end of their third year 
must be included the haddock, though some of these may reach maturity 
at the close of two years, the common dab and the long rough dab. 
Amongst the latter two species, indeed, the male comes to maturity a year 
earlier than the female, when two years of age, a phenomenon common to 
most flat-fishes 
Thus, with the witch, the male matures at three years and the female 
at four years; among plaice the male matures at four years and the 
female at five. Among round fishes, on the other hand, the two sexes 
reach maturity at the same age. 
The cod does not attain its mature condition before the completion of 
its fourth year, while such large flat-fishes as the turbot, halibut, and brill 
take a longer time—the turbot probably not before it is seven years old, 
and the brill not before it is five or six. The approximate age at which 
the angler first spawns is, as the minimum, four years for the male and five 
years for the female. 
How many years fish live after they reach sexual maturity it would be 
difficult to decide ; but it is certain that in most cases the duration of 
reproductive life greatly exceeds the immature period. The method of 
determining the age by a study of the measurements is not well suited to 
solve the question, owing to the fusion of the groups from the variations 
in the rate of growth, and it is here that the method of estimating the 
age by the markings or number of zones on the hard structures may be 
of special advantage. Fishes of a size above the normal limit for the 
species are very old. When dealing with the plaice in a previous report* 
I remarked that the largest specimens I then described must be sixteen 
years old, but Professor Heincke, from an examination of the bones of the 
gill-cover, concludes that such individuals are twenty years old and more. 
INFLUENCE OF ExTERNAL ConpDITIONS. 
Among the conditions which influence growth the most important, 
apart from quantity of food, appears to be temperature. Direct experi- 
ments on this point, by keeping fishes in water of different temperature, 
are described in the Zwenty-second Annual Report, where it is shown 
that those in the water that was warmest grew much faster than those in 
colder water. Previous experiments in tanks,t in which the fish were 
retained over winter and supplied with water from the beach at the ordinary 
temperatures, proved that the growth of plaice of 13 and 14 inches and 
of dabs is almost or quite arrested in January and February. It has alsu 
‘ been shown that the growth of small plaice and dabs on the beaches 
ceases in winter, and that among such round fishes as the haddock and 
whiting the retardation of growth is marked in the early months of the 
year, when the temperature is low, the growth of these fishes taking place 
mostly in a few months in summer. 
With regard to the whiting, I have been struck with the attenuation 
shown by many individuals examined in the early part of the year, and 
I think it is not improbable that the storage of fat in the muscles and the 
liver of fishes during summer and autumn is not merely for supplying 
* Twentieth Annual Report, Part III., p 357. 
+ Eleventh Annual Report, Part III., p. 193. 
