0.2 



0.3 



LENGTH (INCH) 



0.4 0.5 0.6 



0.7 



>- 

 o 



z 



O 



80 

 40 



80 



40 



80 



40 



80 

 40 



80 



40 



80 

 40 



80 

 40 



80 



40 

 



SEP 



N = 32 



_^a_ 



OCT 



N=4 



NOV. 



N = 99 



DEC. 



N=I9I 



JAN. 



N= 185 



FEB. 



N=333 



MAR. 



N=2II 



APR. 



N = 88 



T 1 1 1 r 



T 



5 6 7 8 9 10 II 12 13 14 15 16 17 

 LENGTH (MM.) 

 Figure 2. — Length-frequency distribution of postlarval 

 brown shrimp, September 1966 to April 1967. 



indicate, therefore, that brown shrimp post- 

 larvae do overwinter. 



Robert F. Tennple, Project Leader 



TAXONOMY AND CULTURE OF 

 SHRIMP LARVAE 



We directed most of our efforts during the 

 year toward growing mass cultures of food 

 for penaeid larvae. Each successive rearing 

 experinnent resulted in increased numbers of 

 postlarvae; 24,000 postlarvae were obtained 

 in the latest rearing trial. A study also was 

 made to deternnine how varying light inten- 

 sities affect larval behavior. 



Changes made in larval culture procedures 

 were to increase the amount of aeration and 

 the supply of food. Aeration was supplied by 

 airstones suspended near the sides of the 

 tank as well as in the center. This added 

 aeration improves water circulation in the 

 tank, which in turn, keeps the algal food in 

 suspension. During the protozoeal stages, 

 we are now adding 1 liter (1.1 quarts) of 

 diatom culture to every 15 liters (4.2 gallons) 

 of water in the larval culture tank (fig. 3). 



Larval Food Studies 



It appears that the largest problem remaining 

 for large-scale larval culture is that of 

 supplying increasing volumes of diatoms as 

 larval shrimp food. Last year, to solve this 

 problem, a series of diatom cultures were 

 started to determine if mass cultures of 

 diatoms could be grown in water from the 

 Laboratory's recirculating sea-water system 

 by adding selected nutrients. Additions of 

 NO3, PO4, EDTA (ethylenediaminetetraace- 

 tate), Fe, and a trace metal mixture were 

 used singly and in combination. The addition 

 of nutrients increased the yield over that 

 obtained in unenriched water from the sea- 

 water system without exception; we were able 

 to nnaintain open 30-liter (8.4-gallon) cultures 

 of both Skeletonema costatum and Thalas - 

 siosira sp. 



The additive supporting the best growth of 

 each diatom differed in different months (table 

 4). No single additive gave consistently better 

 growth, but the combination of nitrate, phos- 

 phate, and EDTA most often supported the 

 best growth of Skeletonema . Both diatoms 

 grew well on the same additives only in 

 September. One peculiarity was that in months 

 when Skeletonema required trace metals, 

 Thalassiosira did not; and when Thalassiosira 

 required them, Skeletonema did not. Never- 

 theless, although both diatoms required dif- 

 ferent additives to sustain highest growth, 

 monthly fluctuations in their growth were 

 similar. In January and February, the un- 

 enriched sea water supported better growth 

 than was obtained throughout the rest of the 

 year, even with the best additives. Results 

 from these experiments suggest that some un- 

 known factor(s) is affecting the growth of both 

 diatoms differently and to a greater extent 

 than the additives being tested. 



Skeletonema usually reached peak numbers 

 in 4 to 5 days; Thalassiosira required 6 or 7 

 days. 



Responses of Larvae to Varying 

 Light Intensities 



To determine the effects of light on larval 

 shrimp behavior, brown shrinnp larvae and 

 postlarvae were placed in a 10-cm. (4-inch) 

 square plastic column 137 cm. (54 inches) 

 high and were exposed to gradually increasing 

 light intensities (from 3 to 960 ft.-c.). Nauplii 

 responded photopositively to low light inten- 

 sities and photonegatively to higher intensities. 

 The attraction to low intensities became less 

 pronounced as development progressed; third 

 myses and postlarvae were not attracted to 

 low intensities. The design of the experiment 

 did not allow us to determine whether the 

 later stages were photonegative or just re- 

 maining on, or near, the bottom in response 

 to gravity or some other factor. 



