Effect of temperature on embryonic development of American shad (Alosa sapidissima)

Temperature is a significant stressor affecting the growth and development of American shad (Alosa sapidissima). This study aims to investigate the effects of different hatching temperatures on the embryonic development and larval hatching of A. sapidissima. Five hatching temperatures were set at 16 ℃, 18 ℃, 20 ℃, 22 ℃, and 24 ℃. The embryonic development and larval survival rates were observed, and the gene expression levels at different embryonic development stages were analyzed at the hatching temperature of 18 ℃. The results showed that complete embryonic development was observed at hatching temperatures of 16 ℃, 18 ℃, 20 ℃, and 22 ℃. As the hatching temperature increased, the total hatching duration decreased. The total duration from fertilization to larval hatching was 103 h 50 min, 84h40min, 78 h 40 min, and 64 h 50 min at hatching temperatures of 16 ℃, 18 ℃, 20 ℃, and 22 ℃, respectively. At hatching temperatures of 18 ℃ and 20 ℃, the hatching rate and larval survival rate significantly increased (P<0.05). At a hatching temperature of 22℃, the embryonic mortality rate was significantly higher than at 16 ℃, 18 ℃, and 20 ℃ (P<0.05). At a hatching temperature of 18 ℃, the genes hif1α, hspb1, fbf1, hec, asgr1, and vegfα were inhibited during the cell proliferation period but were significantly activated during the cell differentiation period (P<0.05). During the hatching and pre-hatching organ formation periods, hec expression was significantly activated (P<0.05). In the early embryonic development stage, sod and gst were highly expressed (P<0.05), while hspb1 and hif1α were highly expressed in the late organ formation and hatching stages (P<0.05). Rbpj was significantly highly expressed during the multi-cellular and blastocyst stages of early embryonic development (P<0.05) and downregulated as embryonic development progressed (P<0.05). The optimal hatching temperature for A. sapidissima is 18-20 ℃. The blastocyst stage is a critical period in the embryonic development of A. sapidissima where the expression of genes related to cell formation and division starts to downregulate, and the expression of genes related to organ formation and cell differentiation is significantly upregulated. This study provides a reference for the early development research and breeding selection of A. sapidissima.