A method to eliminate self-fertilization in a simultaneous hermaphrodite scallop. 1. Effects on growth and survival of larvae and juveniles

Abstract

Argopecten purpuratus, as several other scallops of commercial importance is a functional hermaphrodite. The usual methods for breeding cause an unavoidable degree of self-fertilization with the subsequent deleterious effects on survival and growth rates. Some researchers have unsuccessfully attempted to eliminate self-fertilization in these bivalves. Applying our knowledge of the cellular mechanisms of spawning in this species we have developed a method by which self-fertilization was eliminated. By this in vitro fertilization method, oocytes were obtained by scraping the female portion of the gonad, meiosis resumption was induced by serotonin, and then the oocytes were fertilized with sperm from different individuals. The progeny obtained by this method were compared with others obtained by cross-fertilization and self-fertilization. In all these procedures, the oocytes were fertilized at a ratio of 60 sperm per oocyte. The fertilization rates and D larvae survival were determined at 2 and 48 h, respectively. After the D larval stage, the hatchery culture of larvae continued as usual with sampling for survival and growth rates every three days. When larvae looked ready to settle and metamorphose, netlon collectors were introduced into the tanks. After 12 days the collectors were placed in 1 mm mesh collection bags and transferred to the sea. Juveniles were brought back to the hatchery every 40–70 days, to be counted, measured, and placed in mesh pearl nets. The assay of the three procedures for fertilization showed similar fertilization rates but low survival for D larvae obtained from the in vitro method. However, this procedure resulted in the highest size and survival rates of larvae. Survival of juveniles coming from this fertilization procedure was also the highest. The growth of juveniles obtained by in vitro fertilization was also higher than that of those obtained by self-fertilization. We conclude that this in vitro fertilization procedure provides a methodology that results in higher survival and growth rates of juveniles than obtained by procedures involving any degree of inbreeding. This in vitro procedure should be applicable to other simultaneous hermaphroditic scallops.