Artificial Breeding of Spondylus aurantius

Abstract

Spondylus aurantius, a member of the Mollusca phylum, Bivalvia class, Pterioida order, and Spondylidae family, is an important economic marine bivalve species that is widely distributed along the warm-water coastal region in Guangdong and Hainan Province in China, and the Philippines. As an important marine commercial bivalve, wild S. aurantius individuals are often captured by local fishermen for their large adductor muscle, which makes delicious seafood, and for their beautiful shells, which are used for displays.According to the China Fishery Statistical Yearbook for 2022, the annual production of cultured mollusks exceeded 15 million tons, with oysters, scallops, and clams accounting for 78.23% of the total aquaculture yield. In southeast coastal provinces, such as Guangdong, Guangxi, and Hainan, the most common cultured mollusks include Hong Kong oysters (Crassostrea hongkongensis), Suminoe oysters (Crassostrea ariakensis), pearl oysters (Pinctada fucata martensii), and noble scallops (Chlamys nobilis). Generally, Hong Kong and Suminoe oysters cannot tolerate high salinity conditions and are often cultured near estuaries; the P. f. martensii industry is rapidly declining because of high mortality rates and nucleus rejection after transplantation in the process of pearl production; and noble scallop rearing, which is primarily practiced in net cages, and a considerable amount of labor is required to clean attachments. Therefore, there is an urgent need to investigate the cultivation of new bivalve species that can adapt to coastal areas with high temperatures and high salinity.Though S. aurantius is traditionally regarded as an edible mollusk, few studies have reported the artificial breeding of this species. In this study, wild adult S. aurantius with shell length of (12.00±1.25) cm and wet body weight of (100.00±5.04) g were selected as the research subjects to artificially ripen mature individuals, observe and compare the development of the embryo and juveniles at different temperatures (28 ℃ and 32 ℃), and study the effects of different substrates and water depths on the adhesion efficiency of juveniles. Our results were as follows: (1) Under artificial conditions, adult S. aurantius gonads could continue to develop and mature, with testes and ovaries filled with milky spermatozoa and orange eggs, respectively; (2) The method of "dry in the shade + flowing water + high temperature" successfully induced spawning and fertilization of S. aurantius; (3) The diameters of fertilized eggs were (130.1±0.3) µm, and the first unequal cleavage was observed 95 min after fertilization. These eggs then developed into multicellular stages (cleavage occurred at approximately 30-min intervals), blastula (after 4–5 h of fertilization), trochophore (after 10–12 h of fertilization), D-shaped larvae (after 25–28 h of fertilization), umbo larvae (after 6–7 d of fertilization), pediveliger (after 14–15 d of fertilization), and juvenile (after 25–27 h of fertilization); (4) Fertilized eggs could develop into the juvenile stage at both 28 ℃ and 32 ℃; however, the survival rates of fertilized eggs under higher temperatures were lower than of those cultured at 28 ℃, although the speed of S. aurantius embryonic development at 32 ℃ was higher than that at lower temperatures; (5) The density of juvenile S. aurantius in deep water (1–1.5 m depth) was evidently higher than that in shallow water (0–0.5 m depth) in an indoor seedling pond (P oyster shells > concrete reels > black shading nets > green polyethylene mesh sheets under indoor conditions, while the densities and growth rate of juvenile S. aurantius attached itself and oyster shells were better after one month culture in the natural coastal area of Wuzhizhou Island, Sanya. In this study, embryonic development in S. aurantius was observed for the first time. Furthermore, the breeding technology of S. aurantius, including the induction of gonadal maturation and spawning, the incubation of fertilized eggs, and the selection of substrates, was established for the first time under artificial conditions, which could contribute to the future large-scale breeding and cultivation of this species.

Keywords

• spondylus aurantius
• artificial breeding
• embryonic development
• juvenile stage
• substrate