FISHERY BULLETIN: VOL. 69, NO. 1 



be proportional to the third power of body length 

 (Bertalanffy, 1951). The observed relationship 

 does not quite conform to the expected. The re- 

 lationship between body length and body di- 

 ameter appears to be linear (Fig. 7); therefore 

 the body volume must be proportional to the 

 third power of the body length. The observed 

 relationship between weight and length could 

 be the result of orthogonal growth of the ap- 

 pendages, which become progressively larger 

 as the animals mature. 



From the average length-weight relationship 

 and the average continuous growth in length 

 curves (Fig. 4 and 5) we have calculated the 

 average growth in weight curves shown in Fig- 

 ure 8. The average continuous growth in length 

 curves represented by the heavy broken lines 

 in Figures 4 and 5 were used to calculate growth 

 in weight, because we assume that growth in 

 organic weight is continuous during intermolt 

 periods even though growth of the integument 

 occurs in discrete steps. The estimated growth 

 in weight of males was extrapolated by eye from 

 age 175 days to age 204 days. We do not have 

 laboratory growth estimates for these larger 

 males, but they occurred in the field population. 

 The average dry weight per egg (140 eggs in 

 sample) was 5.5 fig. Larvae weigh slightly 

 less than this because they lose weight through 

 metabolism while in the brood pouch, even 

 though their ash content is slightly higher than 

 that of the eggs. 



Figure 7. — Relationship between body length and body 

 diameter of Metamysidopsis. 



Figure 8.— Average growth in dry weight of Meta- 

 mydisopsis females and males in the laboratory. 



REPRODUCTION 



Data on reproduction and associated energy 

 use are easier to obtain for Mysidae than for 

 most pelagic invertebrates. The eggs and larvae 

 are carried in the brood pouch of the female, 

 and the incipient eggs can be counted prior to 

 their full development and extrusion because the 

 body walls of the mysids are transparent. In 

 addition, copulation and fertilization can be ob- 

 served in the laboratory, and frequency of preg- 

 nancy among mature females can be observed 

 in the natural population through sequential 

 sampling because all stages live in the same area 

 while gestating as they do when not reproducing. 

 Nevertheless, average reproduction rate in these 

 animals is not easy to assess with absolute 

 certainty. 



FECUNDITY 



Minimum Estimate 



The most straightforward way to estimate 

 fecundity is to collect animals in the field, pre- 

 serve them, and count the number of eggs or 

 larvae carried by females of diff"erent sizes. 

 Figure 9 shows the relationship between body 

 lengths and number of young for 310 females 

 collected in the field at various times during 

 the year. The data include 125 females bearing 

 eggs and 185 bearing larvae; we excluded ani- 

 mals that had obviously lost young during cap- 

 ture and preservation. For both eggs and lar- 



100 



