Abstract:Tachypleus tridentatus is a rare marine living fossil with immense economic and scientific research value. However, recently, over fishing and indiscriminate killing have led to a sharp decline in the number of horseshoe crabs. Artificial release proliferation is not only an important way to recover horseshoe crab populations, but also to protect biodiversity and promote the sustainable development of fishery. We conducted a preliminary study on artificial breeding of horseshoe crabs T. tridentatus in Zhanjiang, Guangdong Province from May to September 2018. When the water temperature was 28℃~ 32℃, salinity was 26~30, and pH was 7.4~7.8, 9 pairs of T. tridentatus laid 87130 eggs with a fertilization rate of 56%~68%. After 45 days, the embryos hatched into the first instars of juvenile T. tridentatus. The hatching rate was 92%, and 48268 T. tridentatus larvae were obtained. To study the correlation between phenotypic traits and body weight, five quantitative traits (carapace length X1, carapace width X2, carapace height X3, abdomen length X4, and body weight Y) of the first instars of T. tridentatus, 500 individuals were measured, and subjected to correlation analysis, multiple regression analysis, path analysis, and determination coefficient analysis. The results showed that there were considerable correlations (P<0.01) among the five measured traits. Path coefficients of various morphological traits for body mass reached a highly significant level (P<0.01), and the largest path coefficient was used in analyzing the width of the head and chest armor. This indicated that the width of the head and chest armor had the greatest direct effect on body mass. The trend of determination coefficient analysis was comparable to that of path analysis. The elevated total determination coefficient (Σd=0.863) between phenotypic features and body weight indicated that the selected traits were practically useful. The multiple regression equation for estimating body weight was Y=‒0.228+0.248X1+0.073X2+0.333X3+0.073X4. It indicates that the carapace width of the first instars of T. tridentatus has the greatest influence on body mass. Therefore, the width of cephalothorax should be the first choice in germplasm evaluation and seedling screening.
