FISHERY BULLETIN: VOL. 69, NO. 1 



(Clutter 1967, 1969). 



As is characteristic of mysids, the eggs and 

 larvae are held by the oostegites (brood pouch) 

 of the adult females until they develop into juve- 

 niles that are similar in form to the adults. 

 The juveniles grow by shedding their exoskel- 

 etons (ecdysis) at intervals that become pro- 

 gressively longer until they reach maturity. 

 Males and females develop distinguishable 

 morphological features during the period of 

 rapid growth prior to maturity. Growth be- 

 comes progressively slower after maturity. Al- 

 though there is no evidence that death occurs 

 because of physiological aging, the maximum 

 age observed was about 9 months. Most animals 

 survive less than 3 months in the natural en- 

 vironment . We assume that most of the na- 

 tural mortality is caused by predation, especially 

 by fishes. 



Some growth experiments have been reported 

 for other species of Mysidae. Blegvad (1922) 

 determined the growth rates of a few individu- 

 als of My sis inernils from first stage juveniles 

 through early maturity. Nouvel and Nouvel 

 (1939) made disjunct determinations of time 

 between molt stages for some size groups of 

 Praunus flexuosis. Nair (1939) observed the 

 time sequence in the egg and larva development 

 of Mesopodopsis orientalis, determined the size 

 and age at liberation, and noted the size at sex- 

 ual maturity of males and females. In his 

 review of growth in some marine Crustacea, 

 Kurata (1960) presented the results of growth 

 studies made by Ishikawa and Oshima on Neo- 

 mysis japonica and by Matsudaira et al. on 

 Gastrosaccus vulgaris. Mauchline (1967) main- 

 tained adult Schistomysis spiritus in the labora- 

 tory, estimated the time they take to attain sex- 

 ual maturity, and estimated the minimum incu- 

 bation time. Considering differences between 

 species, sizes, and environmental temperatures, 

 these reported patterns of development and size 

 increase per molt are compatible with the results 

 of our study. 



CULTURE METHODS 



Experimental animals were collected during 

 the day from the middle of their habitat with 



nets (Clutter, 1965; Fager, Flechsig, Ford, 

 Clutter, and Ghelardi, 1966). They were placed 

 in large (20-50 liter), opaque plastic containei's 

 with covers and transported to the laboratory 

 within 1 to 2 hr after the time of capture. 



The culture methods were about the same as 

 those described by Lasker and Theilacker (1965) 

 for euphausid shrimps. Individual animals were 

 placed in rectangular clear plastic containers in 

 about 500 ml of sea water. The small con- 

 tainers were partly immei-sed in trays of run- 

 ning sea water. Since the running sea water 

 was pumped continuously into the aquarium 

 from midwater ofl'shore, within the Metamysi- 

 dopsis habitation zone, the laboratory temper- 

 atures ( 14°-20° C) were about the same as those 

 that the animals would have experienced in their 

 natural environment. 



Animals of both sexes and of several sizes 

 were selected for the e.xperiments. Young ju- 

 veniles were procured by j^lacing pregnant fe- 

 males in containers and recovering the young on 

 the day following their release from the brood 

 pouch, which occurred at night. These young 

 were then placed in separate containers. To 

 determine the incubation time, i.e. the time from 

 fertilization of the eggs to release from the brood 

 pouch as juveniles, pregnant females with 

 known times of fertilization were placed in in- 

 dividual containers so that larval development 

 could be observed. 



Mysids of all ages were fed freshly hatched 

 nauplius larvae of brine shrimp, (Artemia sa- 

 lina). Twice each week the mysids were re- 

 moved while their containers were emptied of 

 excess food and cleaned with hot fresh water 

 followed by a sea water rinse. They were then 

 provided with excess quantities of fresh nauplii 

 in clean sea water. 



The containers were examined every day for 

 the presence of molts or, occasionally, carcasses. 

 The molts and carcasses were removed and 

 placed individually in small vials of 5 % Forma- 

 lin for subsequent microscopical examination 

 and measurement. 



OOGENESIS AND INCUBATION 



Since Metamysidopsis has a transparent cara- 



94 



