L92 



Pari III. — Eleventh Annual Report 



II. — Rate of Growth. 



As has been stated, the abrasion caused by the silk cord interferes 

 materially with the rate of growth of the fish, and a glance at the Tables 

 will show, especially in the case of plaice, how few, comparatively, indicated 

 an increase of growth, and that in most cases only to a very slight degree. 

 All the fish returned were carefully measured by myself ; in many cases 

 they had been for a day or two out of the water and had shrunk a little, 

 but experiments on this point made it clear that this shrinkage did not 

 account for much of the decrease in length. Most of the fish, especially 

 the plaice, were thin and poor-looking, but some were fairly plump, and 

 this was especially so with the cod and dabs. In none of the plaice 

 recovered was the reproductive organ much developed, although several 

 were caught at or about the spawning period, and were, or would have been 

 under normal (jrowth, of a size at which reproduction, in the male at all 

 events, would have been possible. It is noted below that a plaice of 10J 

 inches may add (at least) nearly 3 inches to its length in less than 

 a year ; and an examination of the Tables show that a number of the 

 marked plaice would have attained 16 and 17 inches had their rate 

 of growth been in similar ratio ; that is to say, they would have become 

 sexually mature. Nevertheless, the reproductive organ was small and very 

 immature ; and further, these fish remained within the territorial waters. 

 It would appear that interference with growth retards the development of 

 the reproductive organ especially, and that fish thus affected may not 

 pass out to the spawning grounds, although they have reached the repro- 

 ductive age. The stimulus of the movement to the spawning ground 

 appears to spring from the growth of the reproductive organ. 



But although the experiments as a whole are not so useful as might have 

 been desired in throwing light upon the rate of growth, some of them 

 furnish important data. In order to provide a basis of comparison, a 

 number of flat fish have been kept by Mr Peter Jamieson in the tanks at 

 Dunbar, and periodically measured and weighed. 



I. Plaice. 



Eighty-one of the marked plaice recovered were measured by me, and 

 of these 35 had increased in length, the greater number by only a 

 fraction of an inch. The fish which was longest in the water (for 819 

 days, or 2 years and 3 months) had only grown from 10§ inches to 

 llf inches; one which was free for 504 days increased in length from 

 10j to 12£ inches; another, after the lapse of 598 days, had increased 

 from llf to 14f inches; a fourth, after 384 days, from 8| to 10 inches ; 

 a fifth, after 354 days, from 8| to 10 J inches ; a sixth, after 587 days, 

 from 9^ to 11 \ inches; a seventh, after 564 days, from 10.^- to 12J 

 inches; an eighth, after 511 days, from 9 J to 10|- inches ; a ninth, after 

 164 days, from 13| to 14J inches ; a tenth, after 438 days, from 

 12 J to 14f inches. The one which had increased most in length 

 was 10| inches when put into the sea, and 13^ when re-captured, 

 353 days afterwards — an increase therefore of nearly 3 inches in less 

 than a year. From the notes I took at the time in regard to the 

 extent of abrasion, it appears that in this case it was not quite 

 healed. In the third specimen, referred to above, which added about 

 2| inches to its length in 598 days, the silk cord was very loose and the 

 abrasion completely healed, the fish being in very good condition. In the 

 sixth specimen the tail was 'badly damaged'; in the seventh specimen 

 the abrasion had healed everywhere, except a small part on the upper 



