Integrated multi-trophic aquaculture of sandfish Holothuria scabra with hard clam Meretrix taiwanica and milkfish Chanos chanos under environmental stress

Holothuria scabra is a commercially valuable sea cucumber considered a promising candidate for integrated aquaculture, yet its large-scale farming remains underdeveloped in Taiwan. This study had dual aims: to evaluate the environmental tolerance of juvenile H. scabra in controlled laboratory trials and to validate its coculture performance with the native clam Meretrix taiwanica and milkfish Chanos chanos in field ponds. Experiments were conducted in both indoor (laboratory) and outdoor (pond) settings. In indoor trials, juveniles were exposed to three temperatures (14 °C, 24 °C, 34 °C), a salinity gradient (10–40 ppt), and two substrate types (sandy vs. muddy) to assess effects on survival and growth. At 24 °C (optimal) and even at 14 °C, survival remained 100% over 1 week, whereas exposure to 34 °C caused near-complete mortality (only 7% survival by day 7). High salinities (30–40 ppt) sustained > 90% survival, whereas low salinities (10–20 ppt) caused 100% mortality within 13 days. Sandy substrate yielded significantly higher survival and growth than muddy substrate (60% vs. 10% survival after 2 weeks). In parallel, field trials (over summer and winter) compared H. scabra survival in clam monoculture sandy-bottom ponds (clam-H. scabra coculture on sandy substrate), muddy-bottom clam monoculture ponds (clam-H. scabra coculture on muddy substrate), and sandy-bottom clam and milkfish coculture ponds (clam-milkfish-H. scabra coculture on sandy substrate). Peak survival (75% by May to Oct.) was observed in clam-H. scabra coculture on sandy substrate, while survival was markedly lower in clam-H. scabra coculture on muddy substrate (37.5%) and clam-milkfish-H. scabra coculture on sandy substrate (50%). This study provides the first empirical coculture baseline for H. scabra in Taiwan, and its findings inform integrated aquaculture system design.