Figure 3. — Bottom sled designed to sample top 1.3 cm. of the substrate. 



as in the water column. The occurrence of 

 these postlarvae in the water column suggests 

 that they are able to tolerate relatively low 

 temperatures and may not have to burrow, 

 at least in temperatures down to 10° C. 



Clarence C. Fischer, Project Leader 



IDENTIFICATION AND CULTURE 

 OF SHRIMP LARVAE 



Our efforts during the past year were con- 

 centrated on rearing larvae of the brown 

 shrimp in large quantities. To supply food 

 for the larval shrimp, we also spent consid- 

 erable time developing a method to grow the 

 diatom, Skeletonema costatum , in mass cul- 

 ture. Substantial progress was made in both 

 endeavors. 



Rearing of Larvae 



Toward the end of the year, 2,889 postlarval 

 brown shrimp were obtained from a 555-liter 

 fiber glass tank in which shrimp had spawned. 

 This was the first time we had been able to 

 rear larvae through to postlarvae in a tank of 

 this size. Mortality was high, primarily be- 

 cause the diatom culture did not attain suffi- 

 cient density for feeding on schedule; the first 

 protozoeae were without sufficient food for a 

 day. After the larvae started to feed, survival 

 was good. 



The water was aerated vigorously and the 

 room was lighted constantly. The turbulence 

 caused by the aeration seemed to keep the 

 larvae from being trapped by surface tension, 

 and at the same tinne, it kept the algae in 

 suspension so that food had to be added only 

 once a day. The water temperature during 

 this experiment varied between 24° C. and 

 29° C. and the salinity was 22 p.p.t. (parts per 

 thousand). 



An 18.5-liter polyurethaune carboy with the 

 bottom cut out was also used as a rearing 

 container. It was inverted, and air was bubbled 

 up through the neck. We kept 17.4 liters of 

 sea water in the carboy and successfully 

 reared 1,032 postlarvae. Estimated survival 

 was about SO percent. 



Larvae of the seabob were reared to post- 

 larvae in mass culture. Seabob larvae given 

 alga- - Gymnodinium splendens , Thalassiosira 

 sp., and Exuviella sp.--had better survival thsm 

 those fed Skeletonema sp. Also, additions of 

 cultures of mixed algae gave better survival 

 of shrimp larvae than additions of their individ- 

 ual components. Sufficient numbers of larvae 

 were preserved for future taxonomic studies. 



In June, larvae of the white shrimp were 

 reared from eggs to postlarvae in the labora- 

 tory for the first time. The fertile eggs were 

 spawned by two females, neither of which had 

 an external spermatophore attached. Because 

 these shrimp are not supposed to have an 

 internal sperm receptacle, we do not know how 

 the eggs were fertilized. In eight inverted 



