RENSEL and PRENTICE: FACTORS CONTROLLING GROWTH AND SURVIVAL 



restricted to the top 10 cm of the net). By feeding 

 on net fouling organisms, the prawns not only 

 make use of a free food supply, but they also pro- 

 vide net cleaning services that would reduce pen 

 maintenance. 



Molting 



The yearling prawns held at Clam Bay showed 

 five major molting peaks. At each peak, a higher 

 percentage of clam fed prawns molted than un- 

 supplemented prawns, but periods of peak molting 

 generally coincided for each group (Figure 9). TWo 

 major molting peaks occurred in the summer 

 about 50 d apart. By winter (November- February), 

 the peaks were about 75 d apart, and by spring the 

 intermolt periods were once again shortened to 

 nearly 50 d. A pattern emerged with molting 

 peaks occurring at either 1.6- or 2.5-mo intervals, 

 depending on season. Rickards (1971) found a 

 highly significant relationship between tempera- 

 ture and frequency of molting for tank-reared, 

 juvenile pink shrimp, Penaeus duorarum. In the 

 present study, the percentage of prawns molting 

 appears related to temperature (Figure 9), but 

 molt frequency is not related since it increases in 

 late winter while water temperatures are still de- 

 pressed. A previous study of juvenile prawns con- 

 cludes that molt frequency decreases with age 

 (Wickens 1972); however, there is no published 

 account for molt frequency of older prawns. 

 Kamiguchi (1971) reported that molt frequency of 

 sexually immature Palaemon pauciden decreased 

 with size until maturity when a constant interval 

 between molting peaks was the rule. 



In the present study, molting patterns may have 

 been affected by changing photoperiod (Aiken 

 1969) and maturation as the prawns became func- 

 tional males midway through the experiment. 



In conclusion, surface waters of Henderson Inlet 

 were unsuitable for prawn culture due to intense 

 plankton blooms and rapid fluctuations of water 

 temperature. These factors outweighed the 

 growth stimulating effects of elevated water 

 temperatures. Clam Bay was suitable for prawn 

 culture although moderate mortalities were as- 

 sociated with plankton blooms and increases of 

 water temperatures. 



ACKNOWLEDGMENTS 



This work was supported in part by the Wash- 

 ington Sea Grant Office and the Weyerhaeuser 

 Company. 



LITERATURE CITED 



AIKEN, D. E. 



1969. Photoperiod, endocrinology and the crustacean molt 

 cycle. Science (Wash., D.C.) 164:149-155. 



Berkeley, a. a. 



1930. The post-embryonic development of the common 

 pandalids of British Columbia. Contrib. Can. Biol. Fish., 

 New Ser. 6:79-163. 

 BRETT, J. R., AND J. E. SHELBOURN. 



1975. Growth rate of youngsockeye salmon, Oncor/iync/ius 

 nerka, in relation to fish size and ration level. J. Fish. 

 Res. Board Can. 32:2103-2110. 

 Butler, T. H. 



1964. Growth, reproduction, and distribution of pandalid 

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

 21:1403-1452. 



Conklen, D. E. 



1975. Nutritional studies of lobsters, Homarus ameri- 

 canus. In K. S. Price, Jr, W. N. Shaw, and K. S. Danberg 

 (editors). First International Conference on Aquaculture 

 Nutrition, p. 287-296. Univ Del. Coll. Mar. Stud. 



FORSTER, J. R. M. 



1970. Further studies on the culture of the prawn, Pal- 

 aemon serratus Pennant, with emphasis on the p)ost-larval 

 stages. Fish. Invest. Minist. Agric, Fish. Food (G.B.), 

 Ser, II, 26(6), 40 p. 



Figure 9. — Yearling spot prawn molting cycle 5-d 

 means) and monthly means and ranges of surface 

 water temperatures at Clam Bay. 



O 



O 



_l 

 ID 

 Q- 

 O 

 CL 



O 



Water Temperature 5m below surface 



Fed prawns 



Unsupplemented prawns 



16 

 15 



14 



13 o" 



12 



Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 



UJ 



II Q: 

 10 I- 

 9 2 

 8 ^ 



6 ^ 







787 



