reared below 23° C. grew slowly and showed little movement, all dying before 

 reaching the first protozoeal stage. Brown shrimp (P. aztecus ) eggs spawned 

 at 22. 5" C. , hatched slowly, and even though the temperature was raised to 

 23. 5" C. prior to hatching, the larvae were never as robust as larvae of S. 

 brevirostris and T. similis, hatching at 24° C. Brown shrimp nauplii that 

 were active at 2375° C. ceased all movement when the temperature was low- 

 ered to 22. 5° C. After the temperature was raised to 25. 5° C. , they again 



became active. 



No optimum temperature was noted for brown shrimp larvae. Larvae 

 of S. brevirostris did best at 24° C. , and those of T. similis at 28° C. 



~ Temperatures that yielded the best results in the laboratory were 



higher than those in the area of the Gulf where the females were taken. Tem- 

 peratures in the Gulf ranged from 20. 5° C. at the bottom to 22. 0° C. at the 



surface. 



Miquel's sea water with soil extract added was found to be a more 

 satisfactory rearing medium than natural sea water. Although, in some in- 

 stances, the total number of larvae reaching Protozoea I was the same in the 

 natural sea-water control, the larvae in the Miquel's were always more active 

 with more setae. It appears that though nauplii do not actively feed, they do 

 utilize some nutrients in the water. 



Efforts to supply a suitable food for the larvae have been unsucess- 

 ful. Protozoea I were introduced into cultures of unidentified diatoms and 

 protozoans. Several of the larvae exhibited trails of fecal material, indicat- 

 ing feeding had occurred, but none molted to Protozoea II. A primary diffi- 

 cxilty is the lack of live specimens to experiment with. In order to secure 

 living protozoeal and mysis stages, live plankton was brought to the laboratory. 

 The penaeid larvae obtained were alive and active. Other organisms in the 

 plankton included carid, sergestid, and mysid larvae, some of which were 

 isolated along with the penaeid larvae. While the nonpenaeid larvae fed and 

 underwent several molts, the penaeid larvae did not appear to feed and died 

 before molting to the next stage. 



In an effort to find characteristics for separating Sicyonia dorsalis 

 from S. brevirostris, we examined and measured 413 Sicyonia protozoeae and 

 mysis~stages from plankton samples. Slight morphological differences were 

 noted in the protozoeal stages only. The protozoeae were separated into two 

 groups by a difference in the pigmentation of the eyes and by the presence or 

 absence of musculature in the rounded lobe, which is the anteriormost portion 

 of the body. A size difference was also apparent between the two groups of 

 larvae. Connparison with larvae reared in the laboratory proved one group 

 to be S. brevirostris. The other group is assigned to S. dorsalis , the only other 

 member of the genus which maintains a sizable adult population within the 

 sampling area. 



29 



