Females held in the bottom cage or in the labora- 

 tory tanks were subject to less ambient light, more 

 stable temperatures, and water below the photo- 

 synthetic zone. The laboratory water system 

 utilizes water pumped from an area 2 m above the 

 sea floor, thereby approximating the water avail- 

 able to the bottom caged prawns. Previous work 

 has shown that juvenile and yearling prawns are 

 sensitive to rapidly fluctuating water tempera- 

 ture, light, and plankton blooms (Rensel and 

 Prentice 1 ). 



A second spawning was recorded for 85.4% of the 

 surviving females. The average carapace length of 

 these spawners was 39.2 mm (SD = 1.31). Eggs 

 developed normally, producing viable larvae, but 

 the fecundity was low, ranging from 10 to 1,000 

 eggs. The fecundity of wild bred stocks is 2.000- 

 5,000 eggs per female. The reduced fecundity in 

 the female prawns spawning for the second time 

 may be due to nutritional or environmental fac- 

 tors. However, in some instances the female 

 prawns were observed actively removing eggs 

 from their own abdomens, using the second 

 pereiopod. In other cases, we observed egg losses 

 during the holding period due to abrasion on the 

 nets and tanks. 



Multiple breeding and spawning are common in 

 other families of caridean shrimps, but among the 

 Pandalidae only P. montagui Leach in the north- 

 eastern Atlantic Ocean has been known to spawn 

 for two consecutive years (Allen 1963). This study 

 shows that female spot prawns can also success- 

 fully breed, spawn, and hatch eggs for a second 

 time. This is important to both the aquaculturist 

 and the field biologist. If multiple breeding also 

 takes place in wild populations, then estimates of 

 year-class recruitment based on single spawning 

 populations are in error. 



Literature Cited 



ALLEN, J. A. 



1963. Observations on the biology of Pandalus montagui 

 [Crustacea: Decapoda]. J. Mar. Biol. Assoc. U.K. 

 43:665-682. 



BUTLER, T. H. 



1964. Growth, reproduction, and distribution of pandalid 

 shrimps in British Columbia. J. Fish. Res. Board Can. 

 21:1403-1452. 



MAHNKKN, C. V. W. 



1975. Status of commercial net-pen farming of Pacific 



salmon in Puget Sound. Proc. 6th Annu. Meet. 



World Maricult. Soc, p. 285-298. 

 PRENTICE, E. F. 



1975. Spot prawn culture: status and potential. In C. W. 



Nyegaard (editor), Proceedings of a Seminar on Shellfish 



Farming in Puget Sound, Oct. 7, 1975, Poulsbo, Wash., p. 



1-11. Wash. State Univ., Coll. Agric, Coop. Ext. Serv., 



Pullman. 



John E. Rensel 

 earl f. Prentice 



Northwest and Alaska Fisheries Center 

 National Marine Fisheries Service, NOAA 

 2725 Montlake Boulevard East 

 Seattle, WA 98112 



EFFECT OF DISSOLVED 



OXYGEN CONCENTRATION AND 



SALINITY ON SWIMMING SPEED OF 



TWO SPECIES OF TUNAS 



Studies on captive skipjack tuna, Katsuwonus 

 pelamis, have determined three physiological 

 parameters that may operate to delimit oceanic 

 distribution of this fish. If 1) a lower temperature 

 limit of 18°C, 2) a size-dependent upper tempera- 

 ture limit, and 3) a lower oxygen limit of 5 ppm are 

 mapped onto the temperature and oxygen levels of 

 the central Pacific area, the resulting model is 

 consistent with many of the peculiar features of 

 the geographical distribution of the skipjack tuna 

 (Barkley et al. 1 ). In particular, the exclusion of 

 adult skipjack tuna from warm, oxygen-poor wa- 

 ters of the eastern tropical Pacific Ocean is 

 explained. 



But the physiological parameters used in the 

 model were either speculative — upper tempera- 

 ture limits — or based upon acute and stressful 

 experimental conditions — lower oxygen and tem- 

 perature limits. Gooding and Neill 2 determined 

 the lower oxygen limit by introducing tunas into a 

 small tank (1.8 x 2.4 x 0.6 m oval) containing 



'Rensel, J. E., and E. F. Prentice. A comparison of growth and 

 survival of cultured spot prawns, Pandalus platyeeros Brandt, at 

 two salmon farming sites in Puget Sound. Unpubl. Manuscr., 

 25 p. Northwest and Alaska Fish. Cent., Natl. Mar. Fish. Serv., 

 NOAA, Seattle. Wash. 



'Barkley, R. A., W. H. Neill, and R. M. Gooding. Skipjack tuna 

 habitat based on temperature and oxygen requirements. 

 Manusc. in prep. Southwest Fish. Cent. Honolulu Lab., Natl. 

 Mar. Fish. Serv., NOAA, Honolulu, HI 96812. (Material pre- 

 sented at 26th Tuna Conference, Lake Arrowhead, Calif., 29 

 Sept.-l Oct. 1975.) 



2 Gooding, R. M., and W. H. Neill. Respiration rates and reac- 

 tions to low oxygen concentrations in skipjack tuna. Katsuwonus 

 pelamis. Manusc. in prep. Southwest Fish. Cent. Honolulu Lab., 

 Natl. Mar. Fish. Serv.. NOAA, Honolulu, HI 96812. 



649 



