Yields of embryos and larvae produced in a "large-scale" hatchery of Holothuria scabra comparing thermal shock and in vitro fertilization methods.

Worldwide, there exist fewer than 10 large-scale hatcheries dedicated to the production of the sea cucumber Holothuria scabra. Most of the existing hatcheries operate at a pilot scale or receive financial support from research programs. Large-scale hatcheries are defined as private industries that annually produce a minimum of 500,000 juveniles and engage in the exportation of several tons of dried product. Here, we present, for the first time, an analysis of the embryo and larval productions from a large-scale hatchery that annually exports over 5 tons of H. scabra trepang. Utilizing this data, we assessed the impact of isolating broodstock in tanks with elevated temperatures for 10 days, referred to as "maturation tanks," on ovarian maturation. Furthermore, we conducted a comparative analysis to assess the effectiveness of thermal shock and in vitro fertilization (IVF) in obtaining embryos and larvae. The analyzed data originated from Indian Ocean Trepang, a private aquaculture company located in Madagascar. Between August 2017 and December 2018, a total of 291 fertilization trials were conducted, involving 6154 females and 2173 males. Over these 17 months, the total number of embryos obtained was 225 million through IVF and 147 million through thermal shock. The number of 3-day-old auricularia larvae obtained at 11 months was 95 million for IVF trials and 51 million for thermal shock trials. The incubation of broodstock in maturation tanks has been found to enhance ovarian maturity, resulting in a notable 1.3 to 1.5-fold increase in the number of ootids. The combined implementation of IVF and thermal shock methods demonstrated a substantial increase in the productivity of the H. scabra hatchery. Thermal shock is comparatively simpler to implement than IVF and yields higher embryo production per trial. However, it is characterized by greater unpredictability and leads to a higher degree of variability in outcomes. IVF offers superior control over fertilization parameters and furnishes valuable insights into the sexual maturity of the broodstock. During challenging periods, such as the cold season or copepod infestations, the implementation of in vitro fertilizations becomes essential for ensuring hatchery profitability. • A precise control of ovarian and oocyte maturations is necessary for sea cucumber hatchery success. • Incubating the broodstock in "maturation tanks" (i.e. , the isolation of breeders in tanks where the daytime temperature is increased by 8 °C, on average) improves ovarian maturity. • Thermal shocks and in vitro fertilization are both beneficial but thermal shocks are more practical. • In vitro fertilization provides valuable insight into broodstock maturity. • In vitro fertilization is critical for hatchery profitability during adverse conditions. [ABSTRACT FROM AUTHOR]