Of lesser importance in the diet of these two 

 species were foraminifera, bryozoa, bran- 

 chiopods, ostracods, barnacles, amphipods, 

 isopods, stonnatopods, penaeid and crangonid 

 shrimp, crabs, spiders, insects, clams, and 

 squid. 



The abundance of plant material and mud 

 and sand in the stomachs of croakers sug- 

 gests that this species forages for food in the 

 vegetation bordering Clear Lake. On the other 

 hand, the paucity of these items in the diet of 



the seatrout suggests that this species forages 

 in more open waters. 



The tabulation and analysis of food data for 

 the dominant species will ultimately include 

 differences in food items based on size, sea- 

 son, and habitat. Food of the nondominant 

 species can be tabulated only as total per- 

 centage frequency of occurrence because so 

 few samples are available. 



Richard A. Diener, Project Leader 



EXPERIMENTAL BIOLOGY PROGRAM 



We continued to study the effects of tem- 

 perature, salinity, light, and food on laboratory- 

 held penaeid shrimp. This information is useful 

 in defining natural nursery areas of various 

 species and in predicting the effects which 

 manmade changes may have upon these areas. 

 Our studies of salinity and temperature re- 

 quirements of connmercially important penaeid 

 shrimp will also be used to establish manage- 

 ment techniques for pond culture. 



During the year, we showed that the ability 

 of shrimp to survive extremes of temperature 

 and salinity depends on the size or age of the 

 animals tested, as well as on the species. Not 

 only are adult brown and white shrimp some- 

 what less tolerant of extrenme conditions than 

 are juveniles, but also postlarvae of various 

 sizes show different tolerances. Laboratory- 

 hatched postlarvae of brown shrinnp that were 

 8 mm. (3/8-inch) in rostrum-telson length 

 are less able to withstand low salinity and 

 temperature than are 12-mm. (l/2-inch) post- 

 larvae. Such information may be of value in 

 determining the size of postlarvae used to 

 stock ponds for shrimp culture. 



We also noted differences in the ability of 

 aninnals to regulate the concentration of their 

 body fluids. Juveniles of white and brown 

 shrimp appear to be better regulators of in- 

 ternal salt content than the adults. This is re- 

 flected in survival of animals exposed to 

 changes in external salinity as well as in the 

 total salt content of the blood. 



Zoula P. Zein-Eldin, Acting Program 

 Leader 



SHRIMP METABOLISM 



Emphasis this year was on a study of the 

 response of individual animals to selected 

 salinities. Previous experiments indicated that 

 postlarval brown and white shrimp could tol- 

 erate wide ranges of salinity. We did not know, 

 however, how salinity affected the individual 

 animal. 



To study the effects of salinity on the indi- 

 vidual, we measured the total osmoconcen- 

 tration and the chloride content of the blood of 



juvenile and adult shrimp taken from different 

 environments. Samples of shrimp blood were 

 drawn either from the heart or from the base 

 of a walking leg (fig. ZZ), The former method 

 was used for the smaller shrimp and the latter 

 when we tested a single shrimp on several 

 successive days. 



To date, we have tested blood sannples from 

 80 brown shrimp (85-210 nnnn. total length; 

 3.3-8.3 inches), 65 white shrimp (80- 140 mnn.; 

 3.1-5.5 inches), and 27 pink shrimp (145-180 

 mnn.; 5.7-7.1 inches). Brown shrimp were 

 exposed either in nature or by acclimation in 

 the laboratory to salinities ranging from 13 to 

 35 p.p.t. White shrimp tested hadbeen exposed 

 to a broader range of salinity; some specimens 

 were obtained from the fresh water of the 

 Trinity River estuary and others had been 

 reared in our Laboratory and gradually accli- 

 mated to 54 p.p.t. Adult pink shrimp tested 

 had been exposed to salinities ranging from 

 17 to 42 p.p.t. 



Neither the brown nor the pink shrimp tested 

 have been able to regulate blood salt concen- 

 tration at low salinity as efficiently as white 

 shrinnp. Furthernnore, adult pink shrimp are 

 less able to withstand lowered salinity than 

 are adult brown shrimp. These differences 

 may be associated with the occurrence of the 

 species in nature. White shrimp are often 

 taken in waters of low salinity, but juvenile 

 and adult brown shrimp are uncommon in such 

 waters. 



Adult brown shrimp were acclimated to 

 specific salinities at two temperatures- -25° 

 and 18° C. (77° and 63° F.)--to see whether 

 temperature influences the ability of the ani- 

 mals to regulate the salt content of the body 

 fluids. Animals at the lower temperature did 

 not appear to regulate as well as aninnals held 

 at 25° C. Similarly, postlarval brown shrinnp 

 were less able to survive salinity changes at 

 low temperatures than at high temperatures. 



An additional study was made this year to 

 determine the energy source used by the 

 penaeids. Determinations of total blood- 

 reducing substances and of blood glucose 

 indicated that only traces of sugar were pres- 

 ent in the blood of adult pink and brown shrimp. 

 The absence of available energy sources in 



28 



