74 



DEPARTMElsT OF TEE ^AYAL SERVICE 



or kernel is considered as the embroyonic beginning and the narrow light band 

 immediately outside as representing the period in the body of the mother prior 

 to birth, since the fish is ovoviviparons. The first dark band represents the 

 remaining part of the winter period following birth, and the next broad light 

 area, the first summer. From this on the dark and light areas represent the 

 succeeding winters and summers' respectively. The otoliths of Zoarces anguil- 

 laris agree with the description given for those of Zoarces viviparus, but there 

 is no evidence as yet to show that the muttonfish is ovoviviparous. Drawings 

 have been made of six otoliths to illustrate the method of calculation and' also to 

 show the changes in shape of the otolith with increasing age (fig. 3). For example, 

 the otolith of fig. 3 (a) was taken on July 16, 1919, from a specimen 9 cm. in length. . 

 It is exactly similar to others taken during the summer from specimens 7-5, 8-0 and 

 8-3 cm. in length. It seems extremely probable that these muttonfish were in their 

 first Tpor 1 ecau?e Zoarces viviparus grows much more rapidly than this, (Fryd loc. 

 c!t.), and in Canadian waters, pollock, cod, haddock and' hake attain considerably 

 greater lengths in their first years. Moreover, specimens 2-5 and 3-7 cm. have been 

 taken in April and a growth of 1-5 cm. per month during the months May, June and 

 July would not be excessive. Uxifortunately these small specimens were preserved in 

 strong formalin and the otoliths disintegrated. The otoliths from the four larger 

 speci'"'" <?how one winter ring. As will be shown later, the reproductive period 

 undoubtedly occurs in the autumn, and therefore the first light area on the otolith 

 probably represents a short period of very rapid growth in the autumn before the 

 onset of winter conditions. 



It should be stated here that in dealing with the otoliths many difficulties 

 occurred. Bands are often indistinct; secondary lines tend to confuse the counts; 

 the lines towards the margins become crowded together. It is a method of age estima- 

 tion, not absolute determination. The difficulties are much the same as those met 

 with in the scales of fish. Lea (1919) expresses the same^'opinion in his work with 

 the scales of herring (Clvpea harengus). "That errors and uncertainty are unavoid- 

 able in investigations of this kind will be admitted by all who have had any experience 

 of such work. The material may be handled with the highest possible degree of care 

 and attention, so as to warrant the hope that a repetition of the determinations must 

 give exactly the same results, yet on going through the whole once more, discrepan- 

 cies will nevertheless be found'. As a matter of fact, we are hardly justified in using 

 the term "age-determination" when dealing with scales; "estimate" would be more 

 correct, for there will always be found, whatever may be the material under consider- 

 ation, a greater or less number of individuals whose scales must be classed as doubtful, 

 and where the decision must be based more or less upon personal judgment." 



