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, or before the close of its second year. Some spawn for the 

 first time at the end of their second year, i.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 Conditions. 



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 Twenty -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 also 

 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. 

 t Eleventh Annual Report, Part III., p. 193. 



