WALSH and LUND: EARLY DEVELOPMENT OF LONGHORN SCULPIN 



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FIGURE 5.— Later postlarval and young stages of the longhorn sculpin, Myoxocephalus octodecemspinosus, artificially propagated in the 

 laboratory: A) late postlarva, 9.0 mm TL (40 d old), scale = 1 mm; B) postlarva prior to transformation to young, 10.5 mmTL(48 d old), scale = 

 1 mm; C) transformed young, 13.0 mm TL (65 d old), scale = 1 mm. Measurements refer to mean total length of larvae and young. 



shoulder spines. Two pairs of nostrils resulted from 

 the completed constriction. The gills had four arches 

 and six branchiostegal rays on each side. 



The earliest indication of the onset of development 

 of adult pigmentation was apparent at about 65 d, in 

 juveniles of about 13.0 mm TL. Dark spots were 

 present at the base of the first dorsal and on the body 

 beneath both dorsals. Melanophores beneath the 

 first dorsal covered the vertical bars which had pre- 

 viously been visible posterior to the auditory region. 

 The other noticeable change in the pigmentation 

 relative to the previous stages was contraction of 

 chromatophores located along the operculum, pec- 

 toral fin bases, and isthmus; these now had the 

 appearance of dense, dark spots rather than large, 

 stellate melanophores (Fig. 5C). 



Juvenile fish of 92-104 d exhibited the characteristic 



four crossbar marks of adults. These fish averaged 

 16.7 mm TL (range 15.2-17.7 mm). Another change 

 in pigmentation was the presence of a line of spots 

 extending from the first crossbar down to and sur- 

 rounding the anal vent. Many of the melanophores of 

 the head and body were reduced in size, so that the 

 basic coloration resulted from the presence of many 

 densely crowded, small melanophores, rather than 

 the large melanophores characteristic of earlier 

 stages. Pigmentation increased at the base of both 

 dorsals and was observed on the anal and caudal fin 

 membranes in a 104-d specimen. A pair of well- 

 developed ridges ran longitudinally along the crown 

 of the head. Supraorbital spines and large head 

 spines were located along the ridges. There were four 

 cheek spines on each side, the uppermost being the 

 largest and the two lowest being quite small. There 



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