Abstract
Summary The histology of the spawning catarina scallop Argopecten ventricosus was studied to characterize cellular and anatomical changes occurring along the gonad-kidney pathway. Broodstock were conditioned for 25–30 days and induced to spawn with two methods: thermal shock and serotonin by intracardiac injection. Samples of the kidney-gonad-digestive gland complex were fixed at the sperm and oocyte stages of gamete emission and at the end of spawning. Both induction methods elicited gametes, and no particular difference in the microscopic anatomy of the acini-kidney pathway was detected. However, serotonin injection, apart from producing a rough valve opening, sporadic movement (opening and closure of valve), and pronounced foot extension, induced gamete emission in less time than thermal shock. Primary gonad ducts opened to acini to permit sperm emission; at the same time, germinal vesicles broke down in female acini and meiosis restarted. Shortly afterward, oocytes gradually changed form from typically poly-hedral to a more malleable form. This probably contributed to oocyte transport through ciliary activity along the gonad and kidney ducts. Nucleoli disintegration, chromosome condensation, and appearance of meiotic figures were observed along the acini-kidney pathway. Although sperm and oocytes were sometimes observed in gonad or kidney ducts, self-fertilization was rarely observed.
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