Culture of the striped venus clam (Chamaelea gallina): effect of temperature on conditioning and spawning, and genetic variability in the progeny

The striped venus clam is an important shellfishery in the Mediterranean, but its populations have declined in several regions. To support recovery and aquaculture development, supplementing wild stocks with hatchery-produced seed is being explored. However, maintaining genetic diversity in these supplemented populations is essential. This study evaluated whether pre-reproductive conditioning of broodstock clams for 4–5 weeks with a microalgae diet (3% of meat dry weight) under two temperature regimes—ambient (FO) and ambient +2 °C (FT)—could improve spawning success and larval viability. Results showed that clams in the FO group displayed better gonadal maturation, and 11 (10%) were successfully induced to spawn using heat shocks (17–27 °C), producing 2.5 million eggs and 2 million larvae, with a 44% survival rate after 21 days. In contrast, the FT group experienced spontaneous spawning during conditioning and produced few larvae with very low survival (<1%). The application of a 29 °C heat shock after the 17–27 °C shocks triggered spawning in many clams from both treatments, but larval survival remained poor. A significant mortality event occurred during post-larval development, although it's unclear whether a summer heatwave (29 °C in the water) or natural mortality during metamorphosis was the main cause. Genetic analysis using 11 microsatellites revealed an 11% decrease in genetic variability and a loss of 14% of parental alleles in the progeny. The study concludes that while springtime conditioning improves control over spawning, better techniques are needed to increase the number of responsive clams and preserve genetic diversity in hatchery-based restocking programs of Chamelea gallina.