The reproductive cycle of the sea cucumber Psolus fabricii was studied in a population from the St. Lawrence Estuary in eastern Canada from May 1988 through August 1989. The gonad consists of numerous germinal tubules which vary greatly in size. The mean diameter of the tubules and gonadal mass follow annual cycles, increasing from early winter through spring, and dropping abruptly during spawning in the summer. Gametogenesis is generally a prolonged process and begins in small tubules in January. By summer the ovarian tubules contain oocytes with a modal diameter of 400-600 {mu}m, and the testicular tubules contain an abundance of early spermatogenic stages, but rarely spermatozoa. These small tubules of the gonad do not spawn until the following year, and there is little gametogenic activity within them until January, when oocyte growth and the production of later spermatogenic stages resumes. The latter production continues until summer and results in a marked increase in the diameter of the tubules. Then, during spawning, these now large fecund tubules are transformed into small tubules. Following spawning, the predominant activity within the spent tubules is phagocytosis of the residual gametes. The active phase of gametogenesis (January to summer) coincides with an increasing photoperiod regime, and an accelerated gametogenesis occurs in March when temperature and food availability begin to increase. Spawning was one month later in 1989 than in 1988 and did not show a consistent relationship with either temperature or light conditions. However, in both years, spawning coincided with a decrease in the freshwater run-off into the Estuary and with the predicted annual increase in phytoplankton.

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The size at sexual maturity, the developmental timing and biology, and the biochemical (protein, glycogen, and lipid) content of eggs and juveniles were determined in two female size groups of the buccinid Buccinum cyaneum. Males reach sexual maturity at a smaller size (27 mm in shell length) than females (37 mm). A total of 33 females spawned in the laboratory starting in November 1991. The egg capsules were concave, measured 6.3 mm in diameter, and contained between 300 and 1000 eggs measuring 240 μm in diameter. Between 1 and 10 embryos developed. The others underwent chromatin degeneration within 3–4 wk and became nurse eggs. Between 1 and 10 crawling juveniles emerged 9 mo later in July and August and measured 2.5 ± 0.3 mm in shell length. The number of eggs and developing embryos within egg capsules increased with the size of the female. However, the quality of the juvenile at hatching, both in size and in biochemical content, did not vary significantly with female size.

In the blue mussel Mytilus edulis, shed oocytes are arrested at metaphase I of meiosis until fertilization. In this study, the mechanisms involved for maintaining the oocytes in metaphase were investigated. Analysis of 35S-methionine-labelled proteins separated by 1D SDS-PAGE reveals that two protein bands of apparent MW of 50 and 54 kDa periodically appear and disappear during meiotic and mitotic cycles. Moreover, the 50 kDa protein band, clearly detected in unfertilized oocytes, is seen to disappear within 15 min after fertilization. Unfertilized or fertilized oocytes treated with emetine have a protein synthesis rate reduced to less than half the normal rate observed in the untreated cells. Addition of this protein synthesis inhibitor at various times after fertilization inhibits the normal progression through the cell cycles. However, emetine added to unfertilized oocytes induces the completion of first meiotic maturation, polar body extrusion, and the decondensation of chromosomes which form one or two large pronuclei. This process is accompanied by DNA synthesis, and is preceded by the early disappearance of the 50 kDa protein band, seen to cycle after fertilization. These results indicate that metaphase arrest, in mussel oocytes, requires the continuous synthesis of short-lived proteins, the destruction of which is sufficient to induce meiosis resumption followed by DNA synthesis.Fertilization in pelecypod mollusc triggers meiosis reinitiation of oocytes arrested in prophase I or metaphase I of meiotic maturation (reviewed by Longo, '83). Early development of pelecypod mollusc embryos has been investigated in various species but, so far, early biochemical events underlying oocyte activation, such as protein synthesis, are best known for the surf clam (Spisula solidisszma) oocytes which are fertilized in prophase I (germinal vesicle stage).In these oocytes, resumption of meiosis after fertilization is controlled by two proteins showing a cycle of appearance-disappearance in phase with stages of the cell cycle, the cyclins A and B (Evans et al., '83). Both cyclins have been shown to have direct meiosis-inducing activity (Swenson et al., '86)' to associate with components of meiosidmitosis-promoting factor (MPF), and to regulate its activity (Westendorf et al., '89; Draetta et al., '89).In contrast to surf clam oocytes fertilized at prophase I, the early fertilization events triggering meiosis resumption in pelecypod mollusc oocytes arrested at metaphase I of meiotic maturation are unknown. Oocytes of the blue mussel arrested in metaphase I of meiotic maturation until fertilization. The metaphase arrest in unfertilized mussel oocytes is likely to be an active process requiring stabilization of MPF activity as best shown for amphibian or mammalian oocytes (reviewed by Masui and Shibuya, '87). Based on the model developed for surf clam oocytes, one prediction is that unfertilized mussel oocytes contain large amounts of cyclins required for maintaining MPF activity and that a n early event of fertilizati...

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