Plans "B," "F," "G," and "I" would isolate 

 vast expanses of the estuary so that they could 

 no longer be used as nursery areas by estuary- 

 dependent species. The proposed shunting of 

 fresh water into eastern Matagorda Bay through 

 adoption of Plans "A" and "E" would simulate 

 the desirable conditions that previously existed 



and now occur in Lavaca Bay, The discharge 

 from the Colorado River will become ex- 

 tremely important for maintaining high-quality 

 estuarine habitat because of plans to divert 

 fresh water from Lavaca Bay. 



Richard A. Diener, Project Leader 



EXPERIMENTAL BIOLOGY PROGRAM 



This program continues the investigation of 

 environmental influences on shrimp. Factors 

 being studied include temperature, light, 

 salinity, parasites, and food. 



Continued research on shrimp parasites 

 revealed that tapeworms common m shrinnp 

 of the Galveston estuary (1) are probably 

 not significant sources of shrimp mortality, 

 (2) will live at least 5 wk. in shrimp, and (3) 

 seem to be much more common in shrinnp 

 from some bays than from others. These 

 findings favor the possible use of parasites 

 as biological shrimp "tags," which may permit 

 the tracing of shrimp stocks from specific 

 bays to offshore fishing areas and spawning 

 grounds. Such a tool would be of considerable 

 value in determining the contribution of specific 

 bays to the offshore fishery. 



Studies of shrimp behavior provided new 

 insight into the swinnming-speed capabilities 

 of postlarvae of brown shrimp and the re- 

 sponses of white shrimp to low tennperatur e. 

 The results will be useful in interpreting the 

 movennents of these animals in nature. 



Experiments on laboratory growth and sur- 

 vival were of several types. The influence of 

 light on growth of postlarval brown shrimp 

 was found to be negligible. This conclusion 

 strengthens confidence in our previous shrimp 

 growth data obtained from experiments re- 

 quiring the use of light. Another study dealt 

 with possible effects of laboratory handling 

 on growth and survival of shrimp. Results 

 indicated no effect, again confirming the re- 

 liability of the methods we use in survival 

 and growth studies. 



Measurements of the efficiency with which 

 individual brown shrimp convert food into 

 growth suggest variation between animals of 

 the same size. This type of variation may 

 cause significant differences between indi- 

 vidual growth rates of shrimp. 



Our research into effects of environmental 

 factors on shrimp growth has thus far been 

 restricted to postlarval and early juvenile 

 stages (up to about 2 in, long). Under labora- 

 tory conditions, growth of shrimp above this 

 size has generally been negligible. Recent 

 studies have been directed toward improving 

 this later growth so that it may be used to 

 measure the suitability of controlled environ- 

 mental conditions for larger shrimp. 



This year saw the successful conclusion of 

 growth and long-term survival studies on young 

 white and brown shrimp. Results of these 

 studies have indicated that there are relatively 

 broad zones of temperature and salinity toler- 

 ance (in terms of survival) for young brown 

 and white shrimp. Growth data demonstrate 

 that temperature has a far more important 

 effect than salinity on the growth of either 

 species during their postlarval and early 

 juvenile stages. 



Experimental comparisons of white shrimp 

 with brown shrimp taken in spring and sum- 

 mer have provided strong evidence for dif- 

 ferences between species in temperature 

 tolerance. This additional knowledge of the 

 environmental requirements of both shrimp 

 species will permit a better understanding 

 of seasonal distribution of shrimp in estuaries. 



The field use of automated temperature- 

 recording equipment has permitted the most 

 complete tennperature characterization to date 

 of two types of estuarine situations available 

 to postlarval and juvenile shrimp. 



David V. Aldrich, Program Leader 



BEHAVTOR AND ECOLOGICAL 

 PARASITOLOGY 



Previous field phases of this project indi- 

 cated that tapeworms are frequent parasites 

 of brown and white shrimp in the Galveston 

 area, and that the infection is acquired during 

 the estuarine portion of the shrimp's life 

 cycle. Continued research has provided in- 

 formation necessary for the evaluation of 

 tapeworms as potential biological "tags" for 

 shrimp. A 5-wk. study of a captive brown 

 shrimp population showed no significant dif- 

 ference between the population's initial inci- 

 dence of tapeworm infection and that of either 

 short- or long-term survivors. The initial 

 incidence of parasites was 83 percent; that 

 of shrimp dying within the first day of captivity 

 was 78 percent. Seventy-five percent of the 

 5-wk, survivors were infected. There were no 

 statistically significant differences between 

 any two of these values. The results suggest 

 that the worms do not contribute either to 

 very short-term or 5-wk, mortality and that 

 the life expectancy of the tapeworm in shrimp 



39 



