KRYGIER and WASMER: NEW NORTHEASTERN PACIFIC PELAGIC PENAEID SHRIMP 



Male 



Female 



30- 



20 



c 



10 





 30 



20 



10 



Night 



n I N=I25 ^ 



• T I T I 1 I I — I — I — I — I 1 — T 



Day 



N=I32 



-I — I — I — r— 1 — r I ' — n — r-1— i 



6 8 10 12 14 16 18 



6 8 10 12 14 16 IB 20 

 Carapace Length (mm) 



Figure 6. -Day and night length-frequency distributions of male 

 and female Bentheogennema burkenroadi n. sp. 



night with no progressive drop in concentration 

 with increased depth to 1,000 m (Table 1). 



The slight upward movement of this species 

 may be related to its morphology. Vinogradov 

 (1968) considers reduced musculature and a thin 

 integument, which we observed in Bentheo- 

 gennema burkenroadi, to be a means of achieving 

 buoyancy. Because of weak swimming muscula- 

 ture, they may swim too slowly to keep pace with 

 the upward movement of the stimulating isolume, 

 resulting in broad day and night distributions 

 (Donaldson 1973). 



REPRODUCTION 



Since penaeid shrimp do not brood their eggs, a 

 description of the breeding cycle must rely on 

 anatomical changes, especially in the development 

 of the ovary and ova. The female reproductive 

 system consists of a bilaterally symmetrical ovary 

 and paired oviducts internally, and externally of a 

 thelycum. Each half of the mature ovary has an 

 anterior lobe angling from the cervical sulcus and 

 almost reaching the base of the eye, and then 

 folding back along itself (Figure la). The 

 anterolateral lobe lies over the hepatopancreas 

 extending approximately one-half the way down 

 the body wall. The posterolateral lobe, of such a 

 mature ovary, will have visible distinct ova, 

 measuring up to 240-288 jum crossectional 

 diameter, and will extend ventrally, making a 

 pouchlike structure at the base of each of the fifth 

 pereiopods (Figure lb). The posterior lobes ex- 

 tend beneath the dorsal abdominal muscle bands. 



becoming swollen in the first abdominal segment 

 and then extending on toward the end of the third 

 segment. Females were considered to have 

 reached maturity after attaining a size of 12 mm 

 c.l. and males at a size of 11 mm c.l. 



The reproductive cycle, as judged from the sex- 

 ual condition of the testis and ovary, appears to 

 consist of a 4- to 6-mo spawning season and a 6- to 

 8-mo resting phase. Based on samples collected in 

 1972 and 1973, the carapace of females in June is 

 fairly rigid, though the ovaries are not ripe. Some 

 males, from external observation, appear to be 

 ready to release sperm, though most display only 

 partial swelling of the terminal ampoule and vas 

 deferens or lack swelling at all. By fall, females 

 exhibit developing ovaries (two females were in 

 spawning condition), and the carapace is corre- 

 spondingly rigid. Most males have full, ripe looking 

 testes and dilated terminal ampoules. By the end 

 of November, spawning is in evidence. Most 

 females are mature with readily distinct ova; some 

 mature females have evidently spawned as the 

 thoracic cavity appears empty; the carapace is 

 correspondingly nonrigid, due to the spent ovary 

 which had crowded much of the other organs; 

 others have developing ovaries distended by small 

 diameter ova. All males at this time have ripe 

 testes and dilated terminal ampoules. By 

 February, 50% of all females exhibit signs of 

 spawning activity; the rest have probably 

 spawned because their thoracic cavities appear 

 empty and the carapace nonrigid due to the flaccid 

 ovary. Most males still exhibit ripe testes and 

 enlarged terminal ampoules. 



The sex ratio for adult males to females (A^ = 

 440), when all tows are included, was: 1:1, 1:1.08, 

 1:1, 1:1.02, and 1.03:1 for the respective cruises. 

 This approximate 1:1 sex ratio, if it applies to all 

 ages, indicates that there is no selective mortality 

 by sex for this species (Geise 1959). 



GROWTH 



If spawning occurs from November through 

 February and young (6-7 mm c.l.) enter the 

 population April through June (Figure 7), the in- 

 tervening egg and larval stages must take 3 to 5 

 mo. Based on size frequency diagnosis, about 12 

 additional months are required to reach maturity 

 (11-12 mm c.l.) and another 5 to 6 mo are required 

 before spawning commences Thus the generation 

 time is estimated to be about 2 yr. The largest 



745 



