A SYSTEM FOR COLLECTING 



LARGE NUMBERS OF LIVE 



POSTLARVAL PENAEID SHRIMP' 



Acquiring large numbers of small marine orga- 

 nisms for experimental or commercial purposes 

 is often hampered by inefficient methods. Means 

 for concentrating organisms and separating de- 

 sired species from the rest of the catch can be 

 particularly troublesome problems. 



For commercial shrimp culture and related re- 

 search, a system is needed whereby large num- 

 bers of postlarval shrimp can be efficiently 

 caught, separated, and held alive in a healthy 

 condition. The shrimp of greatest interest for 

 pond culture include the tropical and subtrop- 

 ical species whose habit of entering estuaries 

 during larval stages and remaining there for 

 several weeks makes them accessible in large 

 numbers to various collecting methods. Two 

 general methods are presently employed to col- 

 lect shrimp for culture. Postlarvae are impound- 

 ed in the Orient by manipulating tidal flow with 

 sluice gates built into the dikes of ponds (Wal- 

 ford, 1958). This method, however, also im- 

 pounds undesirable species that enter with the 

 small shrimp. Fishermen of the Philippine Is- 

 lands catch shrimp larvae by immersing bundles 

 of grass at the edges of mangrove thickets and 

 periodically removing the attached postlarvae 

 with a dip net, or by dipping a triangular net 

 into the water (Caces-Borja and Rasalan, 1968) . 

 These methods are time-consuming, and the 

 number of postlarvae caught varies greatly 

 among localities; often catches are too small 

 to provide stock for a successful crop. 



The objective of this study was to develop 

 more efficient methods for collecting and sep- 

 arating large numbers of postlarval brown 

 shrimp, Penaeiis aztecus. Postlarvae of this 

 species immigrate through tidal passes on flood 

 tides from February through September along 

 the Texas coast with peak abundance occurring 

 during late winter and early spring (Baxter and 

 Renfro, 1966). The postlarvae occur in great 



numbers near the surface, especially in the more 

 shallow areas (Duronslet, Lyon, and Marullo, 

 in press) and are about 11 mm in total length 

 and 1 mm in diameter at immigration. 



Description of Equipment 



The collecting system, designed for use on a 

 13-m vessel, is shown in Figures 1 and 2. The 

 telescoping outriggers consist of a pipe frame 

 attached to the vessel and pipe extensions which 

 slide inside the frame. The frame itself was 

 constructed from two pieces of 76-mm (outside 

 diameter) galvanized pipe bolted side-by-side to 

 the top of the cabin. The extensions were 51-mm 

 (outside diameter) galvanized pipe. Holes were 

 drilled in the pipes so that each could be ex- 

 tended 2.4 m and secured with a steel pin. 



^ Contribution No. 336, National Marine Fisheries 

 Service, Gulf Coastal Fisheries Center, Galveston Lab- 

 oratory, Galveston, TX 77550. 



Figure 1. — Schematic drawing of collecting system: 

 1 - bow bridles; 2 - staywires; 3 - outrigger frame; 

 4 - outrigger; 5 - double block; 6 -net bridle; 7 - trash 

 screen; 8 -net frame; 9 - net; 10 -funnel; 11 - suction 

 hose; 12 - screw valve; 13 - pump; 14 - sorting box; 

 15 - holding tank. 



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