artificial sea-water media, treating these with antibiotics, various chemicals, 

 and ultra-violet radiation, and by gentle preheating. Transfer of eggs and 

 larvae through serial baths of clean water was also tried. None of these meth- 

 ods, however, proved entirely satisfactory. Better results are now being ob- 

 tained using a circulating rearing medium which is first passed through glass 

 wool and cellulose ("Aqua-pure", Cuno) filters and then irradiated ("Steritron", 

 Englehard Hanovia, Inc. ). 



Identification of larvae 



On several occasions larvae and postlarvae were 



brought to the laboratory for rearing to identifiable sizes. Some were reared 

 in isolation, attempts being made to recover casts for descriptive purposes 

 from each instar. Although this technique has proved feasible in the case of 

 postlarvae, casts from nauplii and protozoea are usually too badly damaged 

 during the molting process to be so utilized. Casts of mysis stages nave not 

 been evaluated. 



Larvae belonging to the genera Penaeus, Sicyonia, Solenocera, and 

 Parapenaeus can now be identified as such using existing reference material. 

 Nauplii and Protozoea I of the species X. krjJyeri and S. brevirostris may be 

 identified through comparison with specimens of known identity reared in the 

 laboratory. 



The concurrent spawning population survey, which employs cytolog- 

 ical techniques to determine extent of gonad maturation, shows promise of also 

 aiding in the identification of larvae. On several occasions, for example, large 

 numbers of larvae identified as Sicyonia sp. occurred together with ripe and 

 spent adults of S. brevirostris, the only Sicyonia species (adults) collected. 

 The conclusion logically following is that the larvae were also largely S. brevi- 

 rostris. 



aOULT FEMALES 



RVAE AND POSTLARVAE 



NUMBER 

 IN 

 STATION SPECIES SAMPLE 



NUMBER 

 IN 

 GENUS SAMPLE 



Coincidence of ripe female and larval shrimp at selected stations, 

 Cruise No. 4 (March 21-23, 1961), spawning population survey. 



16 



