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JOHN S. PEARSE 



Daniel P. Costa 



Marc b. Yellin 



Catherine R. Agegian 



Center for Coastal Marine Studies 

 University of California, Santa Cruz 

 Santa Cruz, CA 95064 



FIRST RECORD OF A SECOND MATING 

 AND SPAWNING OF THE SPOT PRAWN, 

 PANDALUS PLATYCEROS, IN CAPTIVITY 



The spot prawn, Pandalus platyceros Brandt, is 

 the largest species of the family Pandalidae. It 

 supports a minor fishery within its range of San 

 Diego to the Bering Strait, Korea, and Japan in 

 depths to 532 m (Butler 1964). The prawn is being 

 studied at the National Marine Fisheries Service 

 (NMFS) Aquaculture Research Station, Manches- 

 ter, Wash., as a possible companion crop to Pacific 

 salmon reared in floating net pens (Mahnken 

 1975; Prentice 1975). One phase of this work is to 

 investigate the reproductive potential of the 

 prawn in captivity. 



The prawn is a protandric hermaphrodite, i.e., 

 an individual matures first as a male (at age 

 1.5 yr), breeds one or more times as a male, passes 

 through a transitional phase (at age 2.5 yr), and 

 becomes a functional female (at age 3.5 yr) (Butler 

 1964). In studies of natural populations in south- 

 ern British Columbia, Butler (1964) found that 

 few if any females breed more than once and 

 suggested that the females die soon after spawn- 

 ing. 



At the Aquaculture Research Station, prawn 

 culture and breeding experiments have been car- 

 ried out since 1973. The matings reported in this 

 study were made with laboratory-cultured males 



and captured, wild females. The females were cap- 

 tured in ovigerous condition in 1974 from Hood 

 Canal, Wash., and their eggs hatched in the 

 laboratory during February and March 1975. 

 Therefore, we know these females have spawned 

 at least once, and since their prior history is un- 

 known, there is the possibility that some or all 

 may have spawned more than once. 



The spawned females (103) were held from 

 March to August at the Aquaculture Research 

 Station in floating net pens or in benthic cages 10 

 m beneath floating net pens containing salmon. 

 The postspawning survival was 100% through 

 August 1975 for both groups. All prawns in the net 

 pens were maintained on a diet of frozen clam 

 meat, Panope generosa, and salmon mortalities. 

 The benthic cage group did not receive any sup- 

 plemental food. 



In August varying densities of spawned females 

 and cultured males (Table 1) were placed either in 

 three net pens, eight laboratory tanks, or in a 

 benthic cage. The net pens were constructed of 

 18-mm mesh (stretch measure) knotless nylon 

 with 6.8 m 2 of substrate per pen available to the 

 prawns. The top of each pen was covered with 

 black plastic sheeting. Each laboratory tank had 

 0.24 m 2 of available substrate. All water entering 

 the tanks was sand filtered and not recycled. The 

 single benthic cage was constructed of vinyl- 

 coated wire mesh (9.0-mm stretched measure) and 

 had 2.6 m 2 of substrate available to the prawns. 

 All test groups were fed the clam-salmon diet 

 with the exception of those in the benthic cage 

 which received no supplemental food. A continu- 

 ous low-level mortality was observed among the 

 females from August to early October 1975 which 

 reduced their survival to 39.8%. 



Survival of the female prawns was not depen- 

 dent upon stocking density; however, survival was 

 significantly greater in the benthic cage and 

 laboratory tanks than in the net pens (Table 1). 



TABLE 1. — Survival (percent in parentheses) and second spawn- 

 ing of female Pandalus platyceros in three seawater systems. 



Container 

 type 



No of prawns 

 per container 



Female 



Male 



Density 



of 

 prawns' 



Survival of 



previously 



spawned 



females 



Survivors 



spawning 



a second 



time 



Benthic cage 



(9 m deep) 



Net pen 1 



Net pen 2 



Net pen 3 



Laboratory 



tanks 2 



'Prawns per square meter of available substrate 

 2 A total of eight laboratory tanks. 



5 

 29 

 24 

 29 



5 

 56 

 43 

 89 



3.8 



12.5 



9.9 



17.4 



16.7 



4 (80 0) 



12(44.8) 



6 (25.0) 



6 (20.7) 



12(75.0) 



3 (75.0) 

 10(84.6) 



4 (66.7) 



5 (83.3) 



12(100 0) 



648 



