- 44 — 

 4. Gadus pollachius Linné, Pollack (Chart II) 



§ 1. Remarks on the identification 



It is sometimes not so very easy to distinguish the somewhat older stages of Gadus 

 virens and pollachius (especially from ca. 15 to ca. 25 mm.) ^ The following characters will 

 as a rule however be sufficient for this purpose : the anus lies further forward in G. pollachius 

 than in G. virens (in front of the middle line in the first, behind this in the second). 

 The preanal ventral pigment is well-marked in the former, weak in the latter. The medio- 

 lateral streak is more conspicuous in the pollack than in the coalfish^, and reaches 

 further forwards, and the fins are likewise more pigmented in the former, especially the 

 caudal. Further reference for the distinguishing characters may be made to my descrip- 

 tion of the two species {"■Gadus", Part I). 



But since, as mentioned, there may be cases where it is difficult to distinguish the 

 somewhat older stages, it is fortunate that we have in the number of vertebrœ a certain 

 means of determination. I may give here the results of our examination of adult pollack '. 

 From these it will be seen that the most frequent number of abdominal vertebrae is 21 

 (from 20 — 22), whereas the coalfish (see p. 35) has 23 — 25. It is therefore only necessary 

 to count the abdominal vertebrae to settle the question. 



vertebra Skager Rak Scotland Channel Total 



20 + 32 1 1 2 



20 + 33 2 .. 2 4 



20 + 34 .. 1 1 



21 + 32 1 .. 15 16 



21+33 1 1 5 7 



21 + 34 .. 1 1 



22 + 32 .. 1 1 



Summary 

 Total No. of vertebrae 52 53 54 55 

 Number of specimens 2 20 9 1 



1 may utilise this occasion to make an addition to my earlier remarks {Gadus, Part 1) 

 on the youngest postlarval stages of the pollack. In my monograph (p. 18) a schematic 

 figure is given of the postanal pigment's arrangement in these stages. At that time I had 



^ I have never had any difficulty in distinguishing the earlier postlarval stages. The pollack is 

 readily separated from the coalfish in these stages by means of its preanal pigment, the fusion of the 

 dorsal and ventral portions of the postanal pigment bars, so that there are continuous dorsal and 

 ventral streaks of pigment postanally (whereas the two postanal bars in the coalfish remain separ- 

 ated for a long time), the extension of the postanal pigment posteriorly further than in the coalfish, the 

 absence of a lighter region medially on the lateral aspect which characterises the coalfish and the 

 more distinct mediolateral streak. 



^ On the other hand the mediolateral streak disappears earlier in the young bottom stages of ca. 3 

 — 5 cm. of the pollack than in the coalfish. 



' The specimens examined from the Channel have been sent me from the Laboratory of the Marine 

 Biological Association in Plymouth, and I would here offer my best thanks to its Director, Dr. E. J. 

 Allen, for sending them. The vertebrae were counted here in Copenhagen by Cand. mag. A. Sïbubbebg. 



I 



