Gametogenesis From the Early History Life Stages of the Kumamoto Oyster Crassostrea sikamea and Their Breeding Potential Evaluation.

Yuehuan Zhang,Zihua Zhou,Ying Pan,Jun Li,Lai Ma,Haitao Ma,Ziniu Yu,Shu Xiao,Yanping Qin

doi:10.3389/fphys.2019.00524

Abstract

The Kumamoto oyster, Crassostrea sikamea, is native to Southeast Asia, including China, Japan and Korea, and is an important traditional wild fishery resource. Although this oyster’s early gametogenesis was reported in Mexico, no related research was found on the breeding potential using early forming gametes. We re-examined the gametogenesis of C. sikamea during early life history in southern China and further divided it into three phases: sex differentiation (1 month old, shell height 2–3 mm), physiological maturity (2 months old, shell height 3–5 mm) and functional maturity (3 months old, shell height 9–12 mm). The breeding potential was evaluated using four sets of gametes from parent oysters of different ages (2, 3, 6, and 15 months old). The physiologically mature gametes were not suitable for artificial hatchery due to the low production of eggs, and yielding a high deformity rate of D larvae (95.47 ± 1.25%) and heavy larval morality (90.23 ± 1.84%) post-fertilization. However, progeny from functionally mature gametes grew significantly faster than those of other age groups, with no significant differences in fertilization, hatching level or survival of progeny among them. This study clearly demonstrates that the first batch of functionally mature gametes can develop normally and produce viable progeny, suggesting that artificial hatchery of C. sikamea is completely feasible using parent oysters from 3 months old and onward. Furthermore, this hatchery method can effectively shorten the breeding cycle and accelerate the breeding process.

Highlights

The reproductive strategies of an organism play a major role in the dynamics of the population and the biogeography and continuity of the species
The gametogenesis process throughout the first 3 months of life was divided into three phases: sex differentiation, physiological maturity and functional maturity
Larvae survival rate was taken as the ratio of the number of eye larvae to the number of D larvae; larvae growth rate was the daily increase in larval shell height; the metamorphic time was defined as the duration length of time between the appearance of D larvae to 90% larval settlement; the metamorphic rate was the ratio of the number of spat to the number of eye larvae; and the metamorphic size was the maximum primary shell height

Summary

Introduction

The reproductive strategies of an organism play a major role in the dynamics of the population and the biogeography and continuity of the species. The Kumamoto oyster Crassostrea sikamea is widely distributed throughout Southeast Asia, including in Japan (Ariake Sea and Seto Inland Sea) (Hedgecock et al, 1993; Hamaguchi et al, 2013), Korea (Suncheon Bay) (Hong et al, 2012) and China (Southern China) (Wang et al, 2013). It occurs naturally in China, and lives in abundance over a wide geographical distribution, ranging from Jiangsu to Guangxi, including Hainan Island (Wang et al, 2013). The wild resource has sharply declined due to environmental pollution and marine land reclamation, so the artificial hatching and culture of C. sikamea was in demand to increase oyster yield (Zhang et al, 2016)

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Conclusion