FISHERY BULLETIN: VOL. 69, NO. I 



shown is the age of the animal at the time it 

 molted, rathei- than the age at the time that the 

 molted integument was first formed. The pro- 

 cedure for combining the various growth curves 

 of individual animals was to first plot the growth 

 of the animals of known age, and then plot the 

 other gro\vth curves (actual ages unknown) in 

 a manner that showed the least variation from 

 the apparent trend. 



Some of the apparent variability in growth 

 rates may be attributable to differences in the 

 temperature at which the growth occurred, but 

 we did not detect any obvious temperature efl^ect. 

 Considerable individual variability occurred 

 among animals of the same size or age that were 

 reared simultaneously. 



Maturation 



Changes in morphology in relation to size, and 

 known or estimated age, wei'e observed in the 

 molts of animals reared in the laboratory. Ob- 

 servations were made on live females collected 

 from the field population to determine the size 

 at which yolk invested ova first appear in the 

 ovaries. Supplementary observations on the re- 

 lationship between size and body form were 

 made on preserved animals that had been col- 

 lected in the field. There is some evidence from 

 previous samples taken for other purposes 

 (Clutter, 1967, 1969) that the relationship be- 

 tween size and stage of development may vary 

 seasonally. But during the period of observa- 

 tions reported here, this did not appear to be 

 significant. 



In particular, we wished to determine (1) 

 the size (and subsequently the age) at which 

 males and females were easily distinguishable 

 by their secondary sexual characteristics, (2) 

 the size at the onset of maturity, and (3) the 

 size at which spawning and brooding of eggs 

 and larvae occurs. The external characteristics 

 that most obviously separate males from females 

 of this species are the enlarged oostegites (brood 

 pouches) of the females and the enlarged pleo- 

 pods (abdominal legs) and antennae of the 

 males. 



There is some variability in the size at which 

 the stages of development occur. Therefore, 



our estimates are average values. The larvae 

 are released and juvenile form is attained at 

 age 10 days; at this time both sexes are about 

 1.2 mm long (body length; excluding antennae, 

 eyes, and tail fan). Males exhibit sub-adult 

 morphology when about 3.7 mm long, and be- 

 come mature at 4.3 mm. Females exhibit sub- 

 adult form at 4.0 mm, the ova become infused 

 with yolk at 4.5 mm, and the eggs are extruded 

 into the brood pouch, fertilized, and incubated 

 at slightly less than 5.2 mm. 



Average Growth in Length 



Average continuous growth curves were fitted 

 by eye to the combined growth data plotted in 

 Figures 2 and 3. These curves are represented 

 by the lower curves (fine, continuous unbroken 

 lines) in Figure 4 (females) and Figure 5 

 (males) . These continuous curves represent the 

 size of the molt at the time — days from fertili- 

 zation — that the molt was shed. Actually the 

 integument of the animal had attained that size 

 by the beginning of the intermolt period in 

 question. The true growth of the integument 

 of the average animal is represented by the stair- 

 step pattern, which is based on the molting fre- 

 quency analysis. The broken curved line of con- 

 tinuous growth (Fig. 4 and 5) represents the 

 probable pattern of temporal change in average 

 organic weight of the animal. This curve con- 

 nects the points halfway betw^een the beginnings 

 and endings of the intermolt periods. 



Since the average sizes at various stages of 

 development were determined, it was possible 

 to estimate the average time schedules of ma- 

 turation and reproduction for females and males 

 on the basis of the growth curves. The average 

 female begins to develop a brood pouch at the 

 seventh molt, 39 days after becoming a fertilized 

 egg. Yolk invested ova begin to be formed at 

 45 days, during the ninth intermolt period; the 

 ova are extruded into the developed brood pouch 

 and fertilized at the beginning of the tenth in- 

 termolt period, at 53 days; and reproduction 

 can occur at 10 day intervals thereafter. 



Males and females gi-ow at rates that are in- 

 distinguishable up to the age of about 30 days, 

 even though the juvenile males molt more fre- 

 quently than juvenile females. After that the 



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