Blood et al.: Embryonic development of Theragra chalcogramma 



219 



3.5 mm SL 



Figure 9 



Illustration of preserved Theragra chalcogramma yolk-sac larva 

 (Matarese et al., 1989). 



yolk surface (Fig. 8F). The dorsal finfold is formed 

 on the posterior 1/3 of the body and pigment on the 

 head extends at least to the posterior margin of the 

 eye (Fig. 7G). The liver is prominent and the heart is 

 beating in the live egg. 



Tail 3/4 around yolk (stage 18) The embryo 

 has 36-41 myomeres. The tip of the tail is tapered 

 and curves away from the longitudinal axis of the 

 embryo (Fig. 7H). The dorsal finfold extends to 

 midbody and pectoral fin buds are prominent. Otic 

 capsules are formed. Large stellate melanophores 

 are scattered over the dorsum, extending just to the 

 midlateral surface; posterior to the anus, two rows 

 of melanophores are seen dorsally and a few are 

 found along the ventral midline (Fig. 8G). The tip 

 of the tail is unpigmented. 



Tail 7/8 around yolk (stage 19) When the 

 embryo has 44-48 myomeres, the dorsal finfold ex- 

 tends anteriorly 2/3 body length, inserting just pos- 

 terior to the pectoral fin buds and centered over the 

 liver (Figs. 71 and 8H). Pigment on the head extends 

 to the middle of the eye. At midbody, pigment is scat- 

 tered on either side of the dorsal midline, extend- 

 ing to just above the lateral midline. Postanal pigment 

 migrates toward the dorsal and ventral midlines. 



Tail full circle around yolk (stage 20) The 

 embryo has 48—49 myomeres and the pancreas is 

 visible adjacent to the liver (Fig. 7J). The embryo 

 now encircles the yolk and the tail tip may reach 

 from near the snout to as far back as the posterior 

 margin of the eye (Fig. 81). Hatching glands, simi- 

 lar to those of other teleosts (Yamagami, 1988), are 

 discernible on the surface of the snout and may 

 extend over the dorsal surface of the eye (Figs. 7 J 

 and 7K). The posterior portion of the eye is pig- 

 mented. Postanal pigment migrates and begins to 

 form the postanal bars found in yolk-sac larvae 

 (Matarese et al., 1989) (Fig. 9). 



Tail 1 1/8 times around yolk (stage 21) The 

 embryo has 49-50 myomeres and the tail tip elon- 



gates, extending beyond the posterior 

 margin of the eye (Fig. 8J). The urinary 

 bladder is visible posterior to the anus 

 (1/3 body length; not shown on figure) 

 and the dorsal finfold extends to mid- 

 brain. Head pigment extends to the 

 anterior margin of the eye (Fig. 7L). 

 The dorsal half of the eye is pigmented. 

 Most body pigment coalesces to three ar- 

 eas: dorsally, on gut; a bar at 1/2 body 

 length; and a bar at 3/4 body length. In 

 the postanal bars, most pigment is along 

 dorsal and ventral midlines; some pig- 

 ment extends onto the lateral body. Pig- 

 ment is scattered on the preanal body. 



Discussion 



Time from first hatch to 50% hatch was inversely 

 related to temperature. Hatch times reflected the 

 effects of temperature described by Yamagami 

 (1988), who demonstrated that the hatching enzyme 

 secreted by the embryo solubilizes the chorion more 

 rapidly at higher temperatures. The first larvae to 

 hatch were stage 20. Early hatching may have been 

 an artifact of rearing conditions. However, hatching 

 glands were present at this stage, which, with the 

 appearance of eye pigment, may correspond to a 

 level of development that would enable these larvae 

 to survive. Early hatching may occur naturally with 

 some frequency. Within batches of walleye pollock 

 larvae from Puget Sound that had been incubated 

 in the laboratory, larvae hatching early grew to an 

 equivalent size as larvae hatching later (larvae 

 hatched on day 1 were the same length at day 3 as 

 larvae hatched on day 3). Those early hatched lar- 

 vae also began to feed at the same time as larvae 

 hatched later. 4 



Rate of development and time to 50% hatch were 

 similar among studies of walleye pollock from the 

 eastern North Pacific, specifically the Gulf of Alaska 

 (Matarese, unpubl. data; Haynes and Ignell, 1983; 

 and this study; Paul 5 ). From data on time (days) to 

 50% hatch for all temperatures reported in all in- 

 cubation studies (Fig. 10), incubation times of west- 

 ern North Pacific walleye pollock are longer than 

 eastern North Pacific walleye pollock. 



This finding appears to conflict with Haynes and 

 Ignell's (1983) comparison with Yusa's (1954) study 

 in which they report similar rates of development 



4 Olla, B. Mark O. Hatfield Marine Science Center, Oregon State 



University, 2030 Marine Science Drive, Newport, OR 97365- 



5297. Pers. commun. 18 August 1992. 

 s Paul, A. J. University of Alaska Fairbanks, Institute of Marine 



Science, Seward Marine Center Lab, P.O. Box 730, Seward, AK 



99664. Unpubl. data. 



