Morphological Variation and Population Dynamics of the Giant Freshwater Prawn Macrobrachium rosenbergii (De Man, 1879) under High Exploitation Pressures in the Mekong Estuaries

Abstract Crustaceans are the principal fishery resources and a vital livelihood source for communities in the Mekong estuaries, with the giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) recognized as the most valuable species. To advance research and conservation of this key resource, the present study investigated female populations of M. rosenbergii across four estuaries of the Mekong River system, including Cua Dai, Ham Luong, Ba Lai, and Co Chien, during both rainy and dry seasons in 2022. The objectives were to characterize the spatial and temporal patterns of morphological variation and to identify the environmental factors governing these changes. Furthermore, population dynamics were assessed to inform strategies for sustainable exploitation and conservation. Results showed that the overall body size of Mekong populations fell within the global variation range but was generally higher than values reported in many other regions. Morphological traits exhibited pronounced seasonal fluctuations, with higher values observed in the rainy season compared to the dry season. Among environmental parameters, pH, dissolved oxygen (DO), and depth emerged as the primary drivers of temporal variation, with DO exerting the most comprehensive influence. The von Bertalanffy growth function was expressed as Lt = 253.25(1 – e–0.59(t + 0.051)), with an asymptotic length (L∞) of 253.25 mm and a growth coefficient (K) of 0.59 yr–1. Mortality estimates included a total mortality rate (Z) of 3.59 yr–1, comprising natural mortality (M) of 0.72 yr–1 and fishing mortality (F) of 2.87 yr–1. The high fishing mortality underscores the substantial exploitation pressure on Mekong populations of M. rosenbergii. Accordingly, the study also proposed sustainable harvesting strategies essential for the conservation and long-term management of this ecologically and economically important species.