NATURE 



\June 13, 1889 



Up to this stage in the life-history of both round and 

 flat tishes it will have been apparent that the efforts of 

 man can have little effect on the vast multitudes of the 

 eggs and minute fishes. His trawl sweeps beneath them, 

 or they are carried harmlessly through its meshes. Not 

 even in the case of a trawl blocked by a fish-basket and 

 several large skate are any likely to occur. No example, 

 indeed, was procured in the trawling expeditions for the 

 Commission under Lord Dalhousie. The hooks of the 

 liners are too large for the mouth at this stage, and hence 

 they escape capture. Their small size and translucency 

 also seem to afford protection in the case of predatory 

 fishes of their own or other kinds, for they are rare, so far 

 as present observation goes, in the stomach of any fish. 

 Their great numbers are doubtless kept in check by some 

 means, and we know that even jelly-fishes {e.g. Pleuro- 

 brachia) are very fond of post-larval fishes. It is only 

 when they become somewhat larger that they are preyed 

 on by their own and other species, and are swept up in 

 thousands by the destructive shrimp-nets on our sandy 

 shores. 



While the little food-fishes are assuming the change of 

 hue indicated in the preceding pages, they in many cases 

 seek the inshore waters ; at least systematic use of the 

 mid-water and other nets proves that at certain seasons 

 they are met with in large numbers at the entrance to 

 bays or off-shore, and that a little later, in the case of the 

 cod from the ist of June onward, they are visible from 

 the rocky margins. The coloration in this species (cod) 

 is now beautifully tessellated, and they swim in groups, 

 often in company with the young green cod, at the margin 

 of the rocks at low water, and in the little tidal bays 

 connected with rock-pools. The latter are often richly 

 clothed with tangles, bladder-weed, red and green sea- 

 weeds, and the green Ulva., amidst the mazes of which 

 the young fishes find both food and shelter, capturing 

 the little Crustaceans (Copepods, Ostracods, and others) 

 swimming there, and snatching the young mussels and 

 minute univalve mollusks from the blades of the seaweeds. 

 To the zoologist few sights are more interesting than to 

 watch the little cod in these fairy lakes, as they swim in 

 shoals against the current, balancing themselves grace- 

 fully in the various eddies by aid of their pectoral fins. 

 In a mixed company, the young cod are easily recognized 

 by their coloration, and the reddish hue of the occiput, 

 for the blood-vessels there shine through the tissues, which 

 generally are more translucent than in the green cod. 



Prof G. O. Sars considered that about this stage there 

 was an intimate connection between them and the hordes 

 of Medusa; {Aurelm and Cyanea) which abound in the 

 inshore waters towards the end of summer. He thought 

 the young cod approached the Medusa for the sake of 

 the minute pelagic animals stupefied by its poisonous 

 threads, and that the fish repaid this favour by picking off 

 a parasitic Crustacean {Hyperia meditsariaii) which clings 

 to the Medusa. Observations, continued for a long period 

 in this country, show however that this connection is only 

 casual and of very little importance, and that certain 

 HypericE are occasionally found in vast numbers in a free 

 condition. 



As the season advances, the young cod are joined off 

 the rocky ledges by a few pollack and whiting, but not by 

 the haddock, which appears to have certain social views 

 of its own — keeping probably a little farther out. The 

 size of this cod late in autumn, as in October, varies, some 

 I caching 4 to 5 inches in length. Their food ranges from 

 zoophytes to crustaceans, mollusks, and small fishes, and 

 in confinement the larger are voracious, an example 

 about 5 inches readily attacking a smaller (3 inches), and 

 swallowing it as far as possible, though for some time a 

 considerable portion of the body and tail of the prey 

 projected from the mouth. Moreover, the tessellated 

 condition becomes less marked, and as they approach 8 

 inches in length a tendency in some to uniformity of tint 



is noticeable. Many of those, however, that continue to- 

 haunt the rocky shores and the tangle-forests beyond low 

 water still retain for some time mottled sides, and they 

 are known by the name of rock-cod. Further, while their 

 growth in the earlier stages is less marked, it is now very 

 rapid — even in confinement. The exact rate of growth in 

 the free condition in the sea is difficult to estimate, but 

 the little cod of an inch and a half to an inch and three- 

 quarters in June reach lengths varying from 3 to 5 inches 

 in autumn, and in the tanks of the laboratory, specimens- 

 5 inches in August attain 8 inches the following March. 

 At Arendal, in Norway, where opportunities for watching 

 the growth of cod in confinement have been supplied with 

 a liberality yet foreign to our country, Dannevig found 

 that the cod of 3 mm. in April reached only 15 mm. in 

 June, a length somewhat at variance with the condition as 

 above stated on our shores. In July they measured 

 2 inches, in September 3^ inches, and in October 

 about 42 inches. The second year they attained 14 to 16 

 inches in length. In artificial circumstances, as well as 

 in nature, it is found that great variation exists in the 

 sizes of the young fishes of the same age, and this varia- 

 tion would not seem to be related to temperature. 



At the stages just mentioned they now come under the 

 notice of both liner and trawler, for young cod 5 or 6 

 inches in length occasionally take a haddock-hook, and 

 those somewhat larger (9 to 18 inches) occur in certain 

 hauls of the trawl, especially off a rocky coast like that of 

 Aberdeenshire, south of Girdleness, as well as on the 

 hooks of the liners on rough ground. Special trips, 

 indeed, were, and perhaps are, made by the liners for the 

 capture of these young cod (termed codling), and thus 

 their numbers are kept in check. 



So far as present observations go, therefore, the young 

 cod in a free condition reach the length of from 4 to 10 

 inches the fifst year, while in the second they attain from^ 

 10 to 20 inches or more. It probably takes 3 or 4 years 

 (and this is the original opinion of Sars) or more, to reach 

 full maturity, and a length of 3 feet or upwards ; though 

 he mentions having seen young cod a foot in length, with 

 mature roe and milt in the fish-market of Christiania. 

 These, however, were probably abnormal examples. 



Let us now glance at the condition in the whiting. Its 

 earlier post-larval stages immediately following those 

 observed in the tanks at the laboratory (for we failed to 

 rear them) are even now somewhat obscure, but they 

 probably approach those of allied forms such as the cod 

 and haddock. The characteristic nature of the larval 

 pigment, however, would lead to the belief that perhaps 

 in the brighter tints {e.g. yellow), differences may occur. 

 Such, however, are lost before they come under observa- 

 tion ; for all these delicate and minute forms are dead 

 before reaching the deck, and indeed considerably 

 altered. The pressure to which they are subjected in the 

 large mid-water net by the crowds of Hydromedusas and 

 Ctenophores alone would suffice for this, and thehandhng 

 of the heavily laden net increases the dangers to forms so 

 fragile. One about 12 mm. shows in spirit the dorsal and 

 anal fins outlined though not separated from each other, 

 and permanent rays occur in them and in the caudal. 

 Minute ventrals are present, while the pectorals form 

 large mobile fans. Groups of black pigment- corpuscles 

 are distributed along the base of the dorsal and anal fins 

 and over the brain, and a similar series occurs along the 

 ventral median line of the abdomen. The sides have 

 these blackish pigment-corpuscles more generally dis- 

 tributed than in the cod. No barbel is noticeable. When 

 a little longer (15 mm.), the species is distinguished from 

 the young cod by a more abundant distribution of black 

 pigment- specks along the sides of the body and on the 

 fins, and by the greater length and diminished depth of 

 the first anal fin. The median line of pigment still runs 

 along the ventral surface of the abdomen. At 20 mm. 

 the characters that distinguish it from the cod of the same 



