Table 5. --Rate of movement of selected larval stages of 

 brown shrimp toward a low- intensity light source 



stages in our Laboratory rather than from 

 collections made in Galveston Pass as in 

 1965. Advantages derived fronn using 

 laboratory-reared stock were: (1) the identity 

 of the species was known and only a single 

 species was involved; (2) the work of making 

 field collections and sorting young shrimp 

 from other organisms was eliminated; (3) the 

 risk of introducing predatory species was 

 eliminated; and (4) spawning date was regu- 

 lated so that shrimp were available for stock- 

 ing in the quantities desired at the time they 

 were needed. We stocked white shrinnp rather 

 than brown shrimp (used in 1965) so that we 

 could connpare growth between species and 

 rearing methods. 



A single 0.05-hectare (l/8-acre) pond, fer- 

 tilized with 1 cubic yard of chicken manure 

 deposited in a single location, was stocked 

 with 4,092 postlarval shrimp in July. 



During the 121 -day study, shrimp growth 

 was initially rapid but decreased toward the 

 end of the experiment (fig. 4). Over the entire 

 period, shrimp grew at an average daily rate 

 of 0.93 mm. (0.037 inch) in length and 0.078 g. 

 (0.003 ounce) in weight, and attained an aver- 

 age size count of 74 tails per pound. In 



1 



-jn- 398 



Figure 4. — Growth of white shrimp expressed as aver- 

 age lengths and weights over a 4-month period (July 21 

 to November 10) in a 0.5-hectare (1/8-acre) rearing 

 pond to which chicken fertilizer was added. 



November, 3,439 shrimp weighing 32.7 kg. 

 (72 pounds) were harvested. The projected 

 yield was 645 kg. per hectare (575 pounds 

 per acre). Survival rate from date of stocking 

 was 84 percent. 



Population Estimates 



At the time of harvesting, a nnark-recapture 

 experiment was made to determine the in- 

 tensity of sampling necessary to arrive at 

 an accurate estimate of the population density. 

 A total of 328 shrimp was taken from the 

 pond, injected with fast green FCF stain, 

 and returned to the pond. Population esti- 

 mates, based on the number of stained and 

 unstained shrimp captured, were made after 

 each of the 27 successive seine hauls required 

 to remove all shrimp from the pond. More 

 than one-half of the population was accounted 

 for before a population estimation accuracy 

 of 90 percent or greater was sustained. 



Overwintering Studies 



Overwintering tests in which white and 

 brown shrimp were held in the san-ie pond 

 indicated that the white shrimp were not as 

 hardy as the brown shrimp. The difference 

 in average size of the two species at the time 

 of the experiment was marked, however; the 

 white shrimp averaged 120 mm. (4.7 inches) 

 in total length and the brown shrinnp, 18 mm. 

 (0.7 inch). All of the white shrimp died after 

 a series of cold fronts in January during 

 which water temperatures dropped to 5° C. 

 (41,0° F.) on three occasions. Most brown 

 shrimp survived but did not grow at water 

 temperatures below 15° C. (59.0° F.). 



Present Activities 



Both 0.05-hectare (l/8-acre) ponds are now 

 being used for growth studies. In the spring of 

 1967, rice husks were distributed in one pond 

 to increase the surface area of the substrate 

 to increase the growth of micro-organisms and 

 to fertilize the pond water inexpensively; the 

 second pond is being used as a control. 



To improve our understanding of the food 

 chain as related to shrimp growth in our 

 ponds, we examined water chemistry, density 

 of particulate nnatter, and densities and com- 

 position of plankton communities in the water 

 column and in the bottom sediments, in Janu- 

 ary to June 1967. 



In April 1967, we stocked each pond with 

 9,000 postlarval brown shrimp which had 

 been reared in the laboratory. Average daily 

 growth of shrimp in both ponds was about 

 1.34 mm. (0.053 inch) in length and 0.075 g. 

 (0.003 ounce) in weight during the first 2-1/2 

 nnonths of the experiment. 



Ray S. Wheeler, Project Leader 



