A long photoperiod following a short one, and low temperature, stimulate gametogenesis in the sea cucumber Holothuria arguinensis

Temperature and photoperiod are critical regulators of reproduction. However, few studies have evaluated experimentally their specific effects on gametogenesis in sea cucumbers. We tested the effect on gametogenesis of combinations of photoperiod and temperature: “accelerated” (long days following short days; a 12 °C deep in temperature), “constant” (constant short photoperiod; constant Spring/Summer temperature) and “natural” conditions (natural photoperiod and temperature). Experiment 1 started in mid-November (after gametogenesis began) and lasted until March. Experiment 2 started in September, after the spawning season (before gametogenesis started), with gonadal biopsy and spawning trials between March and May. In both experiments, the most advanced gonad development was found in accelerated photoperiod and temperature, with more than 50 % of the sea cucumbers reaching maturity and having the longest and thickest gonadal tubules. However, gametogenesis could not progress in sea cucumbers (i.e. , shortest and thinnest gonad tubules) under constant short photoperiod combined with accelerated temperature. This indicates that a constant short photoperiod inhibits gametogenesis and that an accelerated thermal cycle cannot trigger gonad development alone. When accelerated photoperiod was combined with either accelerated or constant temperature, gametogenesis progressed, advancing faster in accelerated than constant temperature, with spawning only seen in these two treatments. This highlights that long days following short days are required for gametogenesis and that temperature has a modulatory role rather than a trigger, with a cool winter period being stimulatory. Altogether, our study provides essential information into environmental factors in sea cucumber reproduction, valuable for broodstock management and sustainable aquaculture. • Most sea cucumbers matured in accelerated temperature and photoperiod. • Gametogenesis is stimulated by long days following short days. • Constant short days (<12 h) inhibit gonad development. • Temperature change alone cannot trigger gametogenesis, but has a modulatory role. • Spawning was obtained in experimentally manipulated sea cucumbers.