Inspection of Gonadal Maturation in Mediterranean Sea Cucumber (Holothuria tubulosa Gmelin 1791) Under a Constant Temperature Regime

This preliminary study explored the effect of a constant thermal regime on gonadal maturation and spawning readiness in the temperate sea cucumber Holothuria tubulosa Gmelin, 1791, under aquaculture conditions. Adult sea cucumbers were conditioned at a constant mean temperature of 23.4 ± 0.4 °C for 30, 60, 90, and 120 days following gonad regression, and gonadal development was assessed using the gonad index (GI). Survival and growth performance were used as references for the tolerance and suitability of sea cucumbers. The effective accumulated temperature (EAT) in the thermally treated groups ranged from 339.9 to 1370.4 °C·d, significantly exceeding that of the wild controls (17.7–247.5 °C·d). While no significant GI changes occurred at 30 and 60 days, individuals exposed for 90 and 120 days exhibited marked gonadal development, with a mean GI of 6.5% at day 120 compared to 3.45% in wild counterparts. Despite accelerated gonad growth, full maturation and spawning were not achieved within the experimental timeframe, indicating that additional environmental and nutritional cues are required. The specific growth rates up to 0.32% d−1 and 100% survival suggest good thermal tolerance of this species. These findings demonstrate that constant thermal regimes may shorten the gonadal development period in H. tubulosa, offering the potential to advance broodstock conditioning. Future studies integrating optimised diets and photoperiod manipulation may enable off-season spawning and improve aquaculture efficiency.