Causal relationships among the body-related and egg-related traits in crayfish: A case study on Turkish freshwater crayfish Pontastacus leptodactylus (Astacidae: Decapoda)

In this study, the direct and indirect causal relationships among the length, weight, egg diameter, egg weight, and egg quantity of female Pontastacus leptodactylus were analyzed using a path analysis. A total of 79 egg-bearing female crayfish with a total weight (WT; 39.1 ± 16 g) and total length (TL; 109.6 ± 18.1 mm), were sampled from Eğirdir Lake, Türkiye, in 2022 and 2023. Significant direct effects were observed several traits, such as crayfish length and weight, weight and egg diameter, length and egg quantity, egg diameter and egg quantity, weight and egg quantity, length and egg weight, and egg quantity and egg weight (p<0.05). These relationships indicate that larger females tend to produce a higher number of eggs and have greater overall reproductive potential. In contrast, no significant relationships were found between length and egg diameter, weight and egg weight, and egg diameter and egg weight (p>0.05), suggesting that body size may not directly influence egg size in this species. Regarding indirect effects, crayfish length was found to significantly influence egg weight through egg quantity (p<0.05). This suggests that larger females indirectly affect egg weight by producing more eggs. Although the direct effect of egg diameter on egg weight was not significant (p>0.05), its indirect effect of egg diameter on egg weight through egg quantity was significant (p<0.05), indicating that egg diameter plays a role in reproductive output through its influence on egg numbers. The findings of this study contribute to a better understanding of the direct and indirect causal relationships between growth-related traits and egg-related traits in freshwater crayfish. These insights can be utilized in sustainable fisheries management and aquaculture practices by informing selective breeding programs to enhance reproductive success or guiding conservation strategies that protect larger females in natural populations.