I08 MARKETABLE BRITISH MARINE FISHES 



become mature. There has been a great agitation on the subject 

 of the destruction of immature fish, and various investigations 

 have been made with the object of ascertaining the size at which 

 maturity is attained. Different methods have been employed by 

 different investigators of the question. The simplest method, 

 which was first employed by Dr. Fulton, was to ascertain the 

 length of the smallest mature, i.e. ripe or nearly ripe, fish captured. 

 From the investigation in connection with which this method 

 was used very extensive information was obtained about the 

 depths and regions where fish of particular sizes were to be 

 found. But further investigation of the relation between size 

 and maturity was required. In his report on the Irish Survey 

 Mr. Holt gave the smallest sizes of ripe or nearly ripe males and 

 females, and in most cases the minimum was considerably lower 

 for the male, as might be supposed, considering that the average 

 size of the males is in many species smaller. But there is 

 another question, namely, the largest size of the immature, for it 

 is found that some fish which are ripe are smaller than others 

 which show no signs of spawning. The solution of this question 

 involves a careful examination of the roe and milt for the purpose 

 of ascertaining how to make sure that a fish is immature, and out 

 of this another question has arisen, namely, ma)- not a fish after 

 spawning return to a condition in which it is impossible to dis- 

 tinguish it from the immature .'' 



Provided the examination is made at a time of }-ear when 

 there are no shotten fish of the species considered, when spawning 

 has scarcely begun, there can be no possibility of confusing- 

 immature and shotten fish. In the plaice, the species to which 

 most attention has been given in this connection, the roe in its 

 immature state is small. It is triangular in shape, and extends 

 back only a short distance between the flesh and the bones 

 behind the belly cavity. A portion of its substance examined 

 with the microscope shows only minute transparent eggs which 

 have no yolk in them. In a spent fish, one which has just finished 

 spawning, the roe is much larger and has thin flaccid walls. A 

 few ripe eggs are usually found in the cavity of the roe, and its 

 substance examined under the microscope shows besides trans- 

 parent eggs a few with yolk. But it is certain that in the plaice 

 the roe soon diminishes in size after spawning, and returns to a 

 condition in which it is difficult if not impossible to distinguish 



