DEVELOPMENTAL RATES AT VARIOUS TEMPERATURES OF EMBRYOS 

 OF THE NORTHERN LOBSTER (Homarus americanus MILNE-EDWARDS) 



Herbert C. Perkins' 



ABSTRACT 



The rates of development, time from extrusion to hatching at various temperatures, and differential de- 

 velopmental rates at the same temperature of lobster embryos are presented. The eyes of the embryos 

 were measured to monitor the rates and degree of embryo development. 



Herrick (1890, 1896) discussed developmental 

 rates for lobster embryos in the early stages at 

 20° to 22° C. Templeman (1940) determined 

 the times required at various temperatures for 

 lobster eggs to reach the 16-cell stage, and up to 

 the formation of eye pigment. The information 

 from these studies is valuable for determining 

 the rates of early development in lobster egg- 

 embryos but is not adequate for the accurate 

 assessment of developing embryos once eye pig- 

 ment has been formed. By monitoring the rate 

 of development of lobster embryos throughout 

 the embryonic period at various temperatures 

 one can predict hatching times of larvae and con- 

 trol hatching times by manipulating the water 

 temperature in tanks holding egg-bearing fe- 

 males, so that larvae can be available over a wide 

 period of time for use in experiments. This 

 paper presents the rates of development and time 

 required to complete the embryonic period by 

 lobster embryos at various temperatures and a 

 method of continually monitoring that develop- 

 ment. The work was conducted at the National 

 Marine Fisheries Service, Biological Laboratory, 

 Boothbay Harbor, Maine, as part of the Labora- 

 tory's investigation of the early life history of 

 the lobster. 



METHODS AND MATERIALS 



Most of the egg-bearing lobsters used in this 

 study came from the offshore canyons of the 



^ National Marine Fisheries Service, Northeast ' Fish- 

 eries Center, Boothbay Harbor Laboratory, W. Boothbay 

 Harbor, ME 04575. 



continental shelf, south and east of New England. 

 A few came from the Boothbay Harbor area and 

 are so noted. All egg-bearing females were kept 

 in tanks at seasonal water temperatures or in 

 water warmed to various constant temperatures. 

 Water from the laboratory's seawater system 

 was piped to the heated tanks at rates consistent 

 with the capacity of the heaters. Salinity aver- 

 aged 31'/( and ranged from 29 to Z2%c throughout 

 the study period. 



Five egg-bearing females were kept in a tank 

 through which natural seawater at seasonal tem- 

 perature was circulated during the development- 

 al period of their eggs. The purpose of holding 

 these females at seasonal temperatures was to 

 determine the rates of development of their em- 

 bryos in a natural temperature regime. Four- 

 teen female lobsters from the offshore canyons, 

 with recently extruded eggs (eggs in prenaupliar 

 condition), were kept at constant temperatures 

 from 6.9° to 24.6° C. The primary objective 

 at the higher temperatures (20°-24.6° C) was 

 to force the eggs to hatch before the time they 

 would do so at seasonal temperatures. Of fur- 

 ther interest was the rate of development of the 

 embryos at constant, rather than fluctuating, 

 temperatures, and the time required for the eggs 

 to hatch at these temperatures from a given 

 point in their development. 



The rates and extent of development of the 

 embryos were determined by measuring the size 

 of their eyes. Measurements were made to the 

 nearest micron with an ocular micrometer in a 

 dissecting microscope at a magnification of 50 x . 

 When measuring an eye, I took its greatest width 

 and greatest length, combined these figures and 



Manuscript accepted July, 1971. 



FISHERY BULLETIN: VOL. 70, NO. 1, 1972. 



95 



