571 



Description of embryonic development of 



Atka mackerel (Pleurogrammus monopterygius) 



Robert R. Lauth (contact author) 

 Deborah M. Blood 



Email address for R.R. Lauth: Bob.Lauth@noaa,gov 



National Oceanic and Atmospheric Administration 



National Marine Fishenes Service 



Alaska Fisheries Science Center 



Resource Assessment and Conservation Engineering Division 



7600 Sand Point Way NE 



Seattle, Washington 98115 



Atka mackerel (Pleurogrammus mon- 

 opterygius) is a hexagrammid fish 

 that inhabits the temperate and 

 subarctic North Pacific Ocean and 

 neighboring seas (Fig. 1). This highly 

 abundant fish is a critically impor- 

 tant prey species (Sinclair and Zeppe- 

 lin, 2002; Zenger, 2004) that supports 

 a directed commercial trawl fishery 

 (Lowe et al., 2006). Atka mackerel is 

 a demersal spawner and males pro- 

 vide parental care to eggs (Zolotov, 

 1993). During breeding periods, sexu- 

 ally mature males aggregate on the 

 bottom at nesting sites where they 

 establish territories (Lauth et al., in 

 press). Sexually mature females peri- 

 odically visit male nesting territories 

 from July to October to spawn batches 

 of demersal egg masses (McDermott 

 and Lowe, 1997; McDermott et al., 

 2007). Individual nests may consist 

 of multiple egg masses deposited by 

 different females, and males defend 

 nesting territories for a protracted 

 period lasting from the time territo- 

 ries are being established until all 

 eggs within the territory are com- 

 pletely hatched (Lauth et al., 2007). 

 Knowledge about the timing of the 

 reproductive cycle and the use of 

 spawning habitat are important for 

 understanding population structure 

 and the dynamics of stock recruit- 

 ment, which in turn are important 

 factors in the management of Atka 

 mackerel populations. 



The male brooding phase of the re- 

 productive cycle has not been a focus 

 of studies despite its critical impor- 

 tance in the propagation and survival 



of Atka mackerel. The incubation 

 period from fertilization to hatching 

 is a good proxy for determining the 

 time that nest-guarding males stay 

 at nesting sites once spawning has 

 ended. There is one published study 

 describing embryonic development of 

 Atka mackerel at 11°C (Gorbunova, 

 1962); however the results are incom- 

 plete and provide only a partial de- 

 scription of embryonic development. 

 An accurate and complete timetable 

 of embryonic development is essential 

 for determining how temperature af- 

 fects the incubation period and the 

 timing of the reproductive cycle in 

 the North Pacific Ocean (Lauth et al., 

 2007). The objective of this study was 

 to determine the incubation period 

 of Atka mackerel embryos by using 

 a controlled water temperature, and 

 to construct a complete embryonic 

 development series, from fertiliza- 

 tion to first hatching, with particular 

 reference to morphological features 

 and pigmentation for categorizing 

 preserved egg specimens. 



Materials and methods 



Eggs used to construct the embryonic 

 development series were obtained by 

 scuba divers from a nearshore Atka 

 mackerel nesting site at Seguam 

 Island in the Aleutian archipelago 

 (Fig. 1) on 7 August 2002. The in situ 

 egg mass was deposited and fertil- 

 ized on a nest at an unknown time 

 between two scuba dives at 1115 and 

 1720 Alaska Daylight Time (ADT). 



For the purpose of this experiment, 

 the time of egg fertilization was 

 assumed to be 6 hours before egg 

 mass collection. The bottom water 

 temperature at the time of the collec- 

 tion dive was 4.1°C 



The egg mass was brought to the 

 surface, separated into two halves, 

 and each half was placed in a four- 

 liter glass jar with seawater and an 

 air stone. The jars with incubat- 

 ing egg masses were secured in a 

 refrigerator set at 6.0°C and water 

 temperature was monitored with a 

 Tidbit Datalogger (Onset Comput- 

 ers, Bourne, MA) that recorded tem- 

 perature once every minute. On 16 

 August 2004, eggs were transported 

 inside thermoses and coolers with ice 

 by air to the Alaska Fisheries Sci- 

 ence Center (AFSC) in Seattle, WA. 

 Upon arrival, the egg masses were 

 placed in two 38-L aquaria housed in 

 a temperature-controlled room main- 

 tained at 6.0°C. Each aquarium was 

 equipped with air pumps, air stones, 

 and a water circulation pump and 

 water flow directed at the eggs. Sea- 

 water for the aquaria was pumped 

 from Puget Sound, WA, run through 

 l-iim filters, sterilized with ultravio- 

 let light, and stored in 200-L plastic 

 barrels. The seawater in the barrels 

 was adjusted to 32-33 ppt by using 

 aquarium salt, and the barrels were 

 kept inside the temperature-con- 

 trolled room at the AFSC to main- 

 tain the same water temperature as 

 that of the aquaria. Half the water 

 volume in the aquaria was changed 

 on a daily basis and incandescent 

 lights were set on automatic timers 

 to simulate daylight from 0600 to 

 1800 Pacific Daylight Time (PDT). 

 Five to ten eggs were sampled every 

 1-3 days from 16 August to hatching 

 and preserved in phosphate-buffered 

 5% formalin solution. Chorions were 

 removed from eggs to facilitate exam- 

 ination of development with a stereo 

 dissecting microscope. Descriptions 

 of obvious morphological features or 

 pigmentation were recorded for each 



Manuscript submitted 31 May 2007 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 29 July 2007 by the Scientific Editor. 



Fish. Bull. 105:571-576 (2007). 



