GRISWOLD and McKENNEY: LARVAL DEVELOPMENT OK SCUP 



TABLE 2. — Summary of fin development sequence in larvae of 

 Stenotomus chrysops. 



stained specimens until the larvae were about 8.0 

 mm, when the larvae had nearly the full complement 

 of 15-16 pectoral rays. 



An anlage of the caudal base can be seen in larvae as 

 small as 3.4 mm. Some of the principal caudal rays 

 are detectable in the finfold of larvae as small as 4.3 

 mm, and are the first rays of any fins to appear. 

 Notochord flexion in our series begins at 4.7 mm. By 

 5.3 mm all of the principal caudal rays are present as 

 are some of the secondary ones. Flexion is complete 

 at about 8.0 mm and the caudal fin begins to fork at 

 about 10 mm. Full complements of caudal rays 

 (9-10+9+8+8-10) are present in larvae 14 mm or 

 longer. Secondary rays develop in a posterior to 

 anterior direction. 



The soft-ray parts of the median fins first develop 

 beginning at 5.3 mm in our series. Anal and dorsal 

 rays develop together. In both fins, the central soft 

 rays develop first. The development of anterior and 

 posterior rays follows rapidly so that when the larvae 

 in our series are >6.0 mm, full complements of 11-12 

 soft rays are present in these fins. Development of 

 the spiny rays in these fins is from posterior to 

 anterior and follows the soft-ray development. An 

 exception is the posteriormost spiny rays in both fins 

 that appear first as soft rays. 



The last fins to appear are the pelvics. Anlagen are 

 first seen in our series in some larvae at 5.7 mm. 

 Other larvae are >7.0 mm long before these anlagen 

 are visible. Development thereafter is from the distal 

 edge medially. Full arrays of 1 spine and 5 soft rays 

 are present in larvae 8.5 mm or longer. 



Adult scup have six pairs of branchiostegals. Five 

 pairs of these are present in a 4.2 mm larva of our 

 series. They were visible in all of our series that were 

 5.0 mm or larger. The sixth pair, the median one, is 

 not visible in some of our larvae even at 16.5 mm. The 

 first five pairs usually appear simultaneously, but the 

 sixth appears later. 



PIGMENT 



Although scup have chromatophores other than 

 melanophores, these faded rapidly after preserva- 

 tion in Formalin. This account is confined to 

 melanophore pigmentation (Fig. 1). Pigmentation 

 other than that by melanophores is extensive on 

 embryos and early larvae and is described and illus- 

 trated by Kuntz and Radcliffe (1917). 



Head Region 



Newly hatched scup have unpigmented eyes. Two 

 rows of stellate melanophores, one on either side, 

 extend from the snout back over the eyes and con- 

 tinue as part of a lateral series on the trunk. At a 

 length of about 2.5 mm there is a hiatus in this series 

 that extends from mideye level to over the visceral 

 sac. 



At 4.0-5.0 mm length, the pattern that will 

 culminate in that of the juvenile has begun to appear. 

 There are few, usually no, melanophores on the dor- 

 sal and lateral parts of the head anterior to the middle 

 of the eyes. However, there are several prominent 

 melanophores on the posterior midbrain and several 

 on the hindbrain. Ventrally there is usually no pig- 

 ment on the head. A few of our specimens have one or 

 two small melanophores. 



Development beyond this stage consists of a 

 gradual increase of pigment on the dorsal and dor- 

 solateral parts of the head. Most of it occurs above 

 mideye level. A few melanophores appear on the 

 snout and below the eye. There is a prominent 

 melanophore, sometimes accompanied by one or two 

 small ones as well, at the articulation of the lower jaw 

 with the quadrate bone. 



Between the head and the trunk pigmentation in the 

 occipital region there is a gap in the dorsal pigment 

 with relatively little pigment in it . This gap is part of 

 the barred pattern of the juvenile. 



Trunk and Tail Region 



At hatching there are two dorsal rows of stellate 

 melanophores extending from the head to beyond 

 myomere 20. They appear to be between myomeres 

 on the myosepta. Occasionally these rows are 

 interrupted by "missing" melanophores. When this 

 is so, the melanophore is usally lower down on the 

 side of the body. A few, usually three or four, 

 melanophores occur at various places on the anterior 

 part of the yolk sac, and there are one or two on the oil 

 globule. Some specimens have widely spaced 

 melanophores on the ventral margin of the tail. 



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