CLUTTER and THEILACKER: PELAGIC MYSID SHRIMP 



frequency or growth rates. Nouvel and Nouvel 

 (1939) stated that the intermolt period for 

 Praunus flexiiosis is least during the warmest 

 months, and the incubatory period is 15 days 

 in August and 3 to 4 weeks in September. Las- 

 ker (1966) showed that Euphausia pacifica in- 

 termolt ijeriods varied as the water temperature 

 fluctuated, and that the intermolt period was 

 shortened by an artificially produced warm per- 

 iod, but that temperatures above 12° C did not 

 accelerate molting further. 



Since we do not have evidence to the contrary, 

 we must assume that our laboratory observa- 

 tions on molting frequency provide adequate 

 average values. From the median values given 

 in Table 1 and estimated average growth rates 

 (see below) we have estimated the molting 

 schedules of females and males from juveniles 

 to mature adults as follows: 



Females: first six molts — 4 days 

 seventh molt — 5 days 

 eighth molt — 6 days 

 ninth molt — 8 days 

 tenth molt and thereafter — 10 days 



IVIales: first four molts — 3 days 



fifth to eighth molts — 4 days 

 ninth and tenth molts — 5 days 

 eleventh molt and thereafter — 

 6 days 



GROWTH AND MATURATION 



Evidence of the temporal sequence of growth 

 and maturation can be obtained from following 

 peaks of abundance of size groups in natural 

 populations. We sequentially sampled the my- 

 sids in the field and observed some shifting peaks. 

 But we consider that the results are not very 

 reliable because of temporal changes in age- 

 specific mortality rates (Fager and Clutter, 

 1968). Therefore, all the age-specific growth 

 estimates presented here were obtained from 

 laboratory studies. 



Observed Gro'wth 



A few mysids were reared in the laboratory 

 from fertilized egg to adult. Several were reared 

 from egg through the juvenile stage. In addi- 



tion, larger numbers of various sizes were col- 

 lected in the field and kept in the laboratory 

 for several molts. 



The growth data from these animals were 

 combined as shown in Figure 2 (females) and 

 Figure 3 (males). The sexes were separated 

 because the growth and molting rates of males 

 and females are different. As they are shown 

 in Figures 2 and 3, these individual growth 

 curves are simplified and slightly incorrect rep- 

 resentations of true growth, for two reasons. 

 First, the growth of the body integument is 

 represented to be continuous, whereas it actually 

 occurs in discrete increments. Second, the age 



Figure 2. — Observed growth in length (from molts) 

 of Metamysidopsis females in the laboratory. 



Figure 3. — Observed growth in length (from molts) 

 of Metamysidopsis males in the laboratory. 



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