NOTE Lauth and Blood: Description of embryonic development of Pleurogrommus monopterygius 



575 



pigment was observed above and below the notochord, 

 posterior to the anus, and extending toward the tail; 

 the ventrolateral series began 2-5 myomeres posterior 

 to the start of the dorsolateral series. On day 65, the 

 external lateral pigment appeared on the posterior 20% 

 of the body above and below the notochord and on the 

 ventrolateral caudal body. From day 71 to 74, there 

 were no appreciable differences between hatched and 

 unhatched embryos (Fig. 3). The internal dorsolateral 

 series began just anterior to the anus and was spaced 

 regularly with about one melanophore per myomere un- 

 til termination at a point even with the dorsal midline 

 series. The internal ventrolateral series began 10-12 

 myomeres posterior to the anus with similar spacing 

 until 80% BL, where it became irregular until terminat- 

 ing three myomeres before the end of the pvm (postanal 

 ventral melanophore) series. The external dorsolateral 

 and ventrolateral pigment covered the posterior 25% of 

 the body; dorsolateral pigment ended even with the dor- 

 sal midline series and the ventrolateral series extended 

 halfway onto the caudal peduncle. Some larvae had one 

 melanophore on the caudal peduncle midway between 

 the last myomere and notochord tip. 



Discussion and conclusions 



This study provides a complete description of embryonic 

 development that details the progression of morphologi- 

 cal features and pigmentation in Atka mackerel embryos 

 from fertilization to first hatching. Daily egg develop- 

 ment did not deviate from known fish embryology, and 

 the incubation period was 74 days at an average daily 

 water temperature of 6.2°C. The formerly published 

 incubation period of 40-45 days at an average water 

 temperature of 11°C was based on a 19-day rearing 

 experiment supplemented with data from in situ egg 

 samples collected from nesting sites (Gorbunova, 1962). 

 Additional imprecision may have been introduced by 

 unregulated and widely varying water temperatures 

 used during the incubation experiment (8-15°C; Gorbu- 

 nova, 1962). Comparing our study with that of Gorbu- 

 nova (1962), we found that incubation time was inversely 

 related to temperature, which is commonly known to be 

 true for fishes (Hempel, 1979). 



A review of the scientific literature on near-bottom 

 water temperatures at North Pacific Ocean nesting sites 

 shows that temperatures are generally within several 

 degrees of the incubation temperature used in our study 

 (6.2°C). At western North Pacific Ocean nesting sites, 

 water temperatures ranged from 2.5° to 8.2°C in 1958 

 (Gorbunova, 1962), and from 4.84° to 8.30°C in 1985 

 and 1992 (Zolotov, 1993). Similarly, across the central 

 and eastern North Pacific Ocean, the mean and stan- 

 dard deviation of water temperature at 106 nesting sites 

 was 5.4°±1.2°C and was as low as 3.9°C (Lauth et al., 

 in press). It is apparent from our study that the use of 

 nesting substrate by males increases substantially with 

 the longer incubation periods caused by lower water 

 temperatures. In such cases where males are guarding 



multiple egg masses at varying developmental stages, 

 the brooding phase will be more protracted than that 

 where there is only a single egg mass. 



Additional controlled rearing experiments at a wider 

 range of water temperatures are needed to determine 

 more accurately how the rate of embryonic develop- 

 ment, and hence male brooding period, is affected. The 

 complete embryonic development series from this study 

 and an empirically derived incubation rate can be used 

 for modeling the relative spawning and hatching dates 

 of egg masses collected from different nesting sites 

 (Lauth et al., 2007). Such an incubation model would be 

 useful for investigating the variability in timing of the 

 reproductive cycle across the broad longitudinal range 

 of Atka mackerel, which is important for conserving 

 and managing Atka mackerel populations and nesting 

 habitat. 



Acknowledgments 



This project was funded by a grant from the National 

 Marine Fisheries Service (NMFS) Essential Fish Habi- 

 tat (EFH) fund. This work would not have been pos- 

 sible without the help of S. Porter and A. Dougherty 

 who taught R. Lauth incubation techniques and let 

 him use their wet lab. B. Vinter drew the illustrations 

 of the Atka mackerel egg and larva. R. Lauth thanks 

 S. Branstitter and the crew from the FV Sea Storm for 

 field support of this research. Many thanks to those who 

 helped with field support, scuba diving, or reviewing this 

 manuscript: B. Dixon, G. Duker, J. Lee, L. Logerwell, S. 

 Lowe, S. McDermott, R. Nelson, C. Rilling, D. Somerton, 

 G. Stauffer, J. Watson, and two anonymous reviewers. 



Literature cited 



Gorbunova, N. N. 



1962. Spawning and development of greenlings (family 

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 p. 121-185. Tr. Inst. Okeanol., Akad. Nauk. SSSR 

 59:118-182. In Russian (translated by Isr. Program. 

 Sci. Trans., 1970). lAvailable from Natl. Tech. Inf. 

 Serv., Springfield, VA, as TT 69-55097 S.] 

 Hempel, G. 



1979. Early life history of marine fish: the egg stage, 

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 N. Hillgruber 



2007. Timing of mating and brooding periods of Atka 

 mackerel (Pleurogrammus monopterygius) in the North 

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 Lauth, R. R., S. W. McEntire, and H. H. Zenger. 



In press. Geographic distribution, depth range, and 

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 Bull. 

 Lowe, S., J. lanelli, M. Wilkins, K. Aydin. R. Lauth, and 

 I. Spies. 



2006. Stock assessment of Aleutian Islands Atka 



