52 SALT-WATER FISHES 



A very important point in the study of the growth and 

 development of important food-fishes is the size at which 

 they become sexually mature. The fruitful source of dis- 

 cussion whether flat-fish should be protected by Parliament 

 from the trawler, or at any rate from the salesman, until 

 they are full-grown or have attained to their extreme length — 

 whether, in fact, it is for the freedom of the undersized or 

 immature that the legislator is called upon to provide — arises 

 in every conference on the subject. There seems to exist 

 in some quarters a vague notion that the two terms have but 

 one meaning, but this is quite erroneous. As already pointed 

 out, fishes, unlike birds and mammals, are capable of growing 

 much larger long after they are sexually mature. In other 

 words, the quantitative changes are independent of the qualita- 

 tive. It is not easy, unless an immense series of mature and 

 immature fish of a species be examined and very carefully 

 measured, to establish exact sizes at which fish from any given 

 locality (this is important) are first mature. Roughly, it has 

 been computed by so high an authority as Dr. Wemyss Fulton* 

 that, irrespective of sex, plaice on the Scotch coast are first 

 mature at I2 in., dabs at 6 in., turbot at i8 in., and cod at 

 20 in. As a rule, also, the males of bony fishes become mature 

 at a smaller length, and probably earlier, than the females. 



* Mcintosh and Masterman, op. cit., p. 108. 



