Introduction
The control of hatchery protocols for seed production of Holothurian species is key for successful aquaculture, ocean ranching, and stock enhancement of these endangered species. Therefore, in this study we present the results of broodstock collection in the wild, transport to the hatchery, conditioning for natural spawning, and embryonic and larval development of Holothuria grisea.
Materials and Methods
Adult H. grisea (n=72) were collected from the wild, off the Brazilian Atlantic coast (27.8° S – 48.6° W) during the Spring (2022). They were placed in a container equipped with pure oxygen supply and transported in a pickup truck for 800 Km. On arrival at the hatchery in Rio Grande (Brazil), they were separated into three tanks in a RAS. During five months the sea cucumber were kept along with juvenile Pogonias courbina (Sciaenidae) and allowed to feed on fish biodeposits and waste feed.
After five months, the sea cucumbers and fish were transferred from these tanks to another RAS, with the same water quality. Two days after transfer, we observed broodstock releasing gametes and less than 1h after that, fertilized eggs were collected from the tank through a sieve (80mm). Eggs were incubated in cylindric-conical tanks using a semi-static system, larviculture was performed in the same tanks. Larvae were fed on microalgae (Chaetoceros calcitrans). Glass plates colonized with the same diatom were placed in the larviculture tanks once the late auricularia stages were observed. The juveniles were later transferred to flat bottom tanks. Embryonic, larval, and early juvenile development were followed using photography taken under a microscope.
Results
Adult individuals kept in a RAS with juvenile P. courbina (Sciaenidae) spawned within a couple of days after they were stimulated by disturbance and movement to new tanks.
The first cleavage was observed approximately 1h after the gametes were released in the broodstock tanks (Figure 1 B). Gastrula were first observed around 30h after fertilization (Figure 1 E). Two days after hatching the early Auricularia stage was first observed (Figure 1 F). The first hyaline spheres were observed 28 days after fertilization (Figure 1 I)
Abundance of larvae decreased with development towards the late auricularia stage. After reaching the doliolaria and pentactula stage, larvae assumed demersal behavior and were no longer available in the water column. Early juveniles were observed in the glass plates placed in the larviculture tanks (Figure L).
Five months after fertilization, juvenile length achieved between 1-2 cm. Their color is yellow, and they are successfully fed on organic debris siphoned out of juvenile P. courbina rearing tanks.
Discussion and conclusion
The results presented here show H grisea can spawn in captivity and the fertilized eggs can develop into juveniles using techniques common to other Holothuriidae species. Adult sea cucumbers kept in a RAS with juvenile P. courbina successfully spawned. Fertilized eggs were successfully collected and transferred to an incubator in a semi-static system. Auricularia larvae fed on microalgae (C. calcitrans) and developed to the juvenile stage.
The description of these breeding techniques is the first step to the introduction of a new species of sea cucumber to aquaculture, allowing diversification of mariculture operations in the Atlantic Ocean, with focus on low trophic species.
Acknowledgements
The authors would like to thank Brazilian CNPq-MCTI, CAPES, and FAPERGS. The support of European Community (AquaVitae Project – H2020 GA:818173) is also appreciated. L.A. Sampaio is a research fellow of CNPq.