18 Fishery Board for Scotland. 



The dift'erences are, on the whole, not very large : in some cases 

 identical measurements were obtained. The differences are due to 

 slight alterations in the body of the fish. It is probably not possible 

 to make the true measurement, because the fish, when laid on its 

 side, is contorted slightly. In the case of the mackerel instances 

 occurred where a character had different sizes on the two sides of 

 the fish. 



Certain characters must be noted on the fishes in a fresh condition. 

 These characters are Nos. XXXI., XXXII., XXXV., and XXXVI., 

 p. 21, and with them the length of the fish should be noted. An 

 additional number of herrings (100 at least) should be used for this 

 pm'pose. In the case of fishes which are preserved in formaline, it 

 is difficult to separate the flesh from the skeleton. If the fish be 

 boiled the skull becomes distorted. 



Drift net herrings are often injured. Where this is evident the 

 fishes should be rejected, so far as the measurements that are likely 

 to be affected therebv are concerned. 



Eacial Description. 



The herrings are to be racially described by the body-characters. 

 These are of two kinds, viz. (1) Measurements on the outside of the 

 body and on parts of the skeleton, and (2) Enumeration-characters, 

 etc. 



In order that the results obtained by different writers be com- 

 parable, it is important that the same list of characters should be 

 adopted by all the investigators, or that there should be a minimum 

 of common cliaracters, while each investigator might add thereto 

 whatever additional characters he might regard as suitable. The 

 larger the number of characters selected the better. 



Further, in the case of the body-measurements, a uniform system 

 of measurement should be adopted. It is not possible to have very 

 minute accuracy in measuring soft bodies : it is well, therefore, to 

 reduce as much as possible the tendency to error, and with that end 

 in view I would suggest the use of the measuring-board * shown in 

 Figs. 5 and 6. By its means the distance of a point from the tip of 

 the lower jaw is given as the projection of the distance on the principal 

 axis. 



Characters. 



The measurements are to be made in millimetres : — 



I. The length of the fish, viz., from the tip of the lower jaw (mouth 

 closed) to the end of the shortest ray in the fork of the tail fin. 



II. Sex. 



III. Maturity, in case of herrings which are not spawning. Breadth 

 of the reproductive organ. Size of the largest ova. 



IV. Girth immediately in front of the dorsal fin. 



V. Girth at the root of the tail. 



The girth is measured by means of a thread drawn gently tense 



* Williamson, H. C, "On the Markerel of the East and West Coasts of Scot- 

 land." 18th Annu'tl Report of the Fishery Board for Scotland for 1899. Pt. III. 

 1900. P. 296 et seq. 



