27 



Irradiate Mackerel to Study 

 Vietnamese Food 



Scientists of the Gloucester Technological 

 Laboratory (Mass.) are using the Marine 

 Products Development Irradiator (MPDI) to 

 sterilize samples of fatty fish fillets (mack- 

 erel) for a Cornell University study. The 

 study involves the manufacture of ' Nuoc- 

 Nam," a fermented fish condiment used a 

 great deal by the Vietnamese. The condiment 

 is made by a process of autolytic degradation 

 of fish protein in strong brine; enzymes from 

 the fish intestines cause the breakdown. The 

 sterilized mackerel fillets will be used to 

 study if and how "Nuoc-Nam" can be made 

 for the Vietnamese. 



Galveston Studies Distribution and 

 Abundance of Shrimp Larvae 



BCF's Biological Laboratory at Galveston, 

 Tex., has begun a study to obtain estimates of 

 the abundance of planktonic -stage Penaeus 

 sp. and to determine their vertical distribu- 

 tion in relation to water temperature. Plank- 

 ton collections are made in waters off Gal- 

 veston ranging from 9 to 55 meters (5-30 

 fathoms) using a Clarke -Bumpus sampler. 

 Four cruises have been completed and the 

 examination of plankton samples begun. 



Also, efforts were resumed to locate con- 

 centrations of Penaeus sp. postlarvae before 

 they enter Galveston Bay. Simultaneous bot- 

 tom-sled and' plankton tows were made in one 

 to 27 meters (| to 15 fathoms). So far, only 

 the sled tows have been examined. Results 

 show that Penaeus sp. are abundant along the 

 bottom inside 9 meters (5 fathoms). During 

 August and September, both white and grooved 

 (either brown or pink) shrimp postlarvae are 

 present in these shallow waters. 



Shrimp Cultivated in Artificial Ponds 



At Galveston, too, about 4,000 postlarval 

 white shrimp, spawned and reared to post- 

 larvae under laboratory conditions, were 

 stocked in one of the |-acre ponds in July. 

 The shrimp were held over an 11 -week peri- 

 od and no water was added or drained. Food 



was provided by fertilizing the pond prior to 

 stocking, and twice thereafter, to induce the 

 growth of plankton. Instead of a commercial 

 fertilizer used in past experiments, chicken 

 manure was applied to a single location with- 

 in the pond. About one cubic yard of fertilizer 

 was used in each application. 



Shrimp grew at an average rate of 1.3 mm. 

 and 0.1 g. per day. They attained a count size 

 of 50 whole shrimp per pound over this 11- 

 week period. During the first 5 weeks, how- 

 ever, they grew rapidly (2.3 mm. and 0.17 g. 

 per day) then a marked decrease in growth 

 was evident --apparently associated with de- 

 crease in plankton density, reflected in the 

 chorimeter values. Additional fertilizer has 

 been applied to the pond to restimulate plank- 

 ton and shrimp growth. 



Studies Life History of 

 Pink Shrimp off Florida 



The Galveston program of nighttime sam- 

 pling of pelagic postlarvae Penaeus sp. (prob- 

 ably P. duorarum) shrimp entering Florida 

 Bay continued during July -September. Semi' 

 monthly plankton samples were collected at 

 the surface, middepth, and bottom of Whale 

 Harbor Channel. From a low in February, 

 the abundance of postlarvae increased grad- 

 ually during the spring. There were peak 

 catches in late May and in July, August, and 

 September. Distribution of postlarvae in the 

 water column was variable --apparently re- 

 lated to the incident light at each level. The 

 highest percentages of postlarvae in the bot- 

 tom nets were obtained near or during the full 

 moon, and when the sky and water were excep- 

 tionally clear; conversely, the highest percent- 

 ages of shrimp in the surface nets were asso- 

 ciated with dark nights and/or turbid waters. 



Daytime suction sampling of benthic post- 

 larval and juvenile Penaeus (8-100 ml. total 

 length) was continued in shallow water sea- 

 grass beds in Florida Bay. A comparison of 

 May -August samples for 196 5 and 1966 showed 

 that the average catchper square meter (m.'^) in 

 1965 was 1.1 shrimp, compared with 1.6 in 1966. 



Exploratory shallow -water shrimp sam- 

 ples were taken in Florida Bay and along the 

 Florida Keys from Key Largo to Big Pine Key. 

 A pushnet and puUnet were used to obtain 

 samples. Young shrimp were particularly 



