水産養殖研究開発ジャーナル

概要

Reproductive Biology and Effect of Arachidonic Acid Level in Broodstock Diet on Final Maturation of the Hawaiian Limpet Cellana sandwicensis

Nhan Thai Hua and Harry Ako

This study examined the natural spawning season of the Hawaiian limpet or opihi Cellana sandwicensis, by
monthly measurement of Gonado Somatic Index (GSI) and histology analysis of the gonad of the animals over the course of a year. The highest GSI values were found in November 2011, January 2012 and from November to December 2012. These GSI values were significantly higher than GSI of opihi collected from other months, suggesting a spawning season for C. sandwicensis from November to January. Significantly lower GSI values were observed from February to September 2012 indicate that opihi were in a resting phase, followed by a final maturation phase which began in October. This study provided an important exogenous key factor for developing an affective induction of opihi gonad maturation in the laboratory. The final maturation of opihi was investigated by supplementation of arachidonic acid (ARA) in the broodstock diet, fed to the animals during the natural final maturation and spawning season. Adult opihi (3.07 ± 0.22 cm in shell length) were fed with two different dietary levels of ARA, 0.24% and 0.39% at the same ARA/EPA (eicosapentaenoic acid) ratio of 0.7 for 95 days. The GSI values of opihi reached to final maturation stage of 24.5% and 23.7% for 0.24% ARA and 0.39% ARA diets respectively, and were significantly higher than GSI of opihi (6.11%) that were fed with the control diet without supplementation of ARA after 75 days. The average eggs diameters were 123 ± 4.23 μm for 0.24% ARA and 121 ± 5.93 μm for 0.39% ARA diets. Histology analysis also confirmed that the eggs were ripe. However, these mature opihi did not undergo to natural spawning and GSI values were winding down after 95 days, suggesting that a natural reabsorption had occurred. The results of this study indicate that supplementation of ARA to EPA ratio of 0.7 during the correct photoperiod were found to have potential for inducing final maturation in limpets.