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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



the pigment cells are arranged in a row along the 

 ventral side of the trunk (p. 203). There is also 

 danger of confusing newly spawned cod eggs with 

 those of the witch flounder (p. 287), which they over- 

 lap in size; but the black pigment of the cod eggs 

 identifies them as gadoid as soon as this appears, 

 for the embryonic pigment of the witch is yellow. 

 (See also haddock on p. 203.) 



Figure 93.- — Diagram of the pigmentation of the young 

 larvae of the cod, A, and of the pollock, B. After 

 Schmidt. 



The larvae are about 4 mm. long at hatching 

 with the vent (which is close behind the yolk sac) 

 located at the base of the ventral fin fold on one 

 side instead of at its margin, so that the intestine 

 seems to end blindly, as is also the case with 

 haddock and pollock larvae. At this stage young 

 cod much resemble the latter, but are separable 

 from them by the fact that the pigment is in two 

 dorsal and three (rarely two) ventral bars, with 

 the dorsal bars shorter than the ventral bars 

 opposite them, whereas the dorsal bars are longer 

 than the opposing ventral bars (fig. 93) in pollock 

 larvae up to 10 mm. long. Neither is there any 

 danger of confusing cod larvae with haddock even 

 at this early stage, for the latter are not barred but 

 have a continuous row of pigment cells along the 

 ventral margin of the trunk behind the vent, 

 besides other patches on the nape and in the 

 lining of the abdomen. 



The young cod float helplessly, when first hatched, 

 yolk uppermost. But they assume the normal 

 position in about 2 days; the yolk being 

 absorbed and the mouth formed in 6 to 12 days, 

 according to temperature, when the larvae are 

 about 4.5 mm. long. As the little cod grows the 



pigment bars gradually fuse, and at 8 to 10 mm. 

 a median band forms. Cod 10 to 20 mm. long may 

 easily be distinguished from pollock by the fact 

 that the pigment extends to the tail, whereas it 

 ends abruptly some distance in front of the tail 

 in the pollock. Haddock of this size show much 

 less pigment (p. 203). Cod fry of 15 to 30 mm. 

 are made recognizeable by the location of the vent 

 under the second dorsal fin, combined with dense 

 pigmentation. At 20 mm. the dorsal and anal 

 fin rays have attained their final number and the 

 separate fins are outlined, while at 30 mm. the 

 fry begin to show the spotted color pattern so 

 characteristic of the cod. 



Rate of growth. — In 1898 a large number of 

 newly hatched larvae were released in December 

 at Woods Hole in the "eel pond" (a lagoon freely 

 communicating with the harbor and with a temper- 

 ature about paralleling that of the outside water), 

 where they grew to an average length of 50 to 100 

 mm. by the following June. 78 The experiment 

 was repeated in the winter of 1899 79 with similar 

 results, as appears from the following table show- 

 ing the growth of approximately 2 million freshly 

 hatched larvae that were placed in the eel pond 

 on January 1 1 . 



Captures of young fry 1% to 3 inches long in the 

 neighborhood of Cape Ann late in June (Earll 

 1880), and subsequently around Woods Hole 

 and on Nantucket Shoals, show that cod hatched 

 from January to March in the Gulf of Maine 

 grow at about this same rate. But fish that are 

 hatched in the rising temperatures of spring 

 might be expected to grow faster during their 

 first few months. European experience 80 is to 

 the effect that young cod are 4% to 8 inches long 

 by the end of then first autumn, which probably 

 applies equally to the Gulf of Maine. 



In later life cod grow at varying rates in different 

 seas, and even fish that are caught in the same haul 



n Bumpus, Science N. Ser., vol. 8, 1898, p. 852. 



'• Smith, Bull. U. S. Fish Comm., vol. 19, 1901, p. 307. 



M Damas (Rapp. et Proces-Verb., Cons. Perm. Intern. Explor. Mer, vol.10, 

 No. 3, 1909) gives an account of the European in .estigations on the life history 

 of the cod, up to that date. 



