The growth, nutrient composition, immune-related gene expression, and Hsp70 protein levels in the juvenile sea cucumber Holothuria scabra: Threshold temperature for normal feeding

Holothuria scabra Jaeger, or sandfish, a commercially valuable yet ecologically vulnerable tropical sea cucumber, is significantly affected by water temperature, particularly the threshold temperatures for normal feeding. In this study, a laboratory trial was conducted to assess the growth, nutrient composition, immune-related gene expression, and Hsp70 protein levels in juvenile H. scabra (average wet weight 1.36 ± 0.22 g) under different threshold water temperatures of 23, 28, and 33℃ for 30 days. The growth results showed that the specific growth rate (SGR) of the juveniles at 33℃ was initially negative during the 0–10 days but significantly increased during the 10–20 days and 20–30 days. The SGR of the juveniles at 28℃ was significantly higher than that at 33℃ (P < 0.001), while juveniles at 33℃ had a significantly higher SGR than those at 23℃(P < 0.001). After 30 days, significant differences were observed in the energy value (P < 0.001) and total amino acids (P = 0.041) of juveniles H. scabra among the 0 days, 23, 28, and 33℃ water temperature groups. The immune genes expression of Hsp70, Hsp90, CuSOD, MnSOD, CAT, and REL in the respiratory tree of juveniles were higher at 23℃ compared to 33℃. Specifically, the Hsp70 protein expression levels in juveniles showed a significant increasing trend over time in the 33℃, whereas the trend was the opposite at 23℃. Overall, short term high water temperatures had a more pronounced impact on H. scabra juveniles compared to short term low water temperatures. Conversely, long term low water temperatures had a more significant effect on juvenile growth compared to long term high water temperatures. These findings enhance our understanding of the adaptive mechanisms of juvenile H. scabra in response to threshold water temperatures for normal feeding, with important implications for aquaculture practices and conservation efforts in China.