Artificial fertilisation method for the production of pen shell Atrina pectinata juveniles in hatcheries

Abstract

In juvenile production of pen shell Atrina pectinata, broodstocks are usually induced to spawn by a combination of a slight increase in water temperature and addition of conspecific sperm to rearing water, but the stimulus is not always effective in eliciting a positive response from ripe adults. To solve the problem of unstable spawning induction, we developed an artificial fertilisation method suitable for the hatchery production of pen shell juveniles. The method was based on our recent finding that all-trans retinoic acid (at-RA) strongly induced the maturation of pen shell oocytes. Experiments were conducted to assess the following: 1) suitable at-RA concentration for oocyte treatment, 2) necessity of at-RA treatment of sperm, 3) optimum egg to sperm ratio, 4) allowable time lag between the at-RA treatment of oocytes and insemination, and 5) possible changes in the performance of the method during the spawning season. In addition, we confirmed the effectiveness of the method by observing the early growth of hatched larvae and the actual production of pen shell juveniles in two separate hatcheries. The recommended conditions were clarified as follows: 1) 1.0 or 0.1 μM at-RA was suitable to prepare mature oocytes, 2) at-RA treatment of sperm was not necessary, 3) optimum egg to sperm ratio was 1:1000, 4) mature oocytes were competent for insemination until 2 h after the at-RA treatment, and 5) fertilisation and hatching rates changed in accordance with alterations in the maturity of broodstocks. In the actual production of juveniles, benthic juveniles of pen shells were successfully obtained at two different hatcheries, although the number of produced juveniles was still small. Increasing familiarity with this new method through repetitive practice, together with the improvement of rearing techniques, would improve the performance of the method. The artificial fertilisation method presented in this article offers a novel alternative for stable production of juvenile pen shells.