Immersed Weight Measurements: A Useful Tool for Estimating Size and Predicting Wet and Dry Body Component Weights of the Sea Cucumber Cucumaria frondosa

The commercial dendrochirotid holothuroid Cucumaria frondosa is characterized by large variability in size, weight, and volume, primarily due to morphological plasticity, which makes the species difficult to assess and describe reliably, especially in a non-destructive way. Here, three different methods for assessing immersed weight were compared. Direct measurement (using a submerged basket attached to a load cell) proved to be the most reliable, showing strong predictive power for body wall dry weights (r2 = 0.86). A proximate-composition-based model incorporating component-specific densities was used to explore how variation in biochemical composition, particularly lipid content in female gonads, may influence overall body density and buoyancy. This study also highlighted the importance of accounting for internal fluid density, including fluid within the coelom and respiratory tree, in interpreting immersed weight measurements. Standardization methods, including conversion mathematical formulas, were developed, tested, and demonstrated, supporting broader application of immersed weight in both research and fisheries contexts. Overall, immersed weight standardized to a common fluid density offers a promising, non-destructive approach for assessing C. frondosa and potentially other sea cucumber species, with applications in monitoring body-component changes, growth studies, stock assessment, and sustainable fisheries management.