Morpho-Taxonomic Characterization of Five Commercially Exploited Decapod Crustaceans (Palaemonoidea and Penaeoidea) from the Barisal Deltaic Region, Bangladesh

In the muddy, shifting waters where the great rivers of southern Bangladesh meet the Bay of Bengal, a complex ecosystem thrives, supporting a vital food source for millions. This deltaic region is home to a diverse community of ten-legged crustaceans, ranging from freshwater prawns that live in the river currents to marine shrimp that inhabit the brackish estuaries. For the local fishermen and the broader economy, these creatures are more than just wildlife; they are a cornerstone of livelihood and food security. However, managing these resources requires a fundamental first step: knowing exactly what is being caught. In the bustling fish markets of Barisal, different species often look remarkably similar, and local names can be confusing, making it difficult to distinguish between a giant freshwater prawn and a marine shrimp. Without clear, scientific identification, it is impossible to track populations accurately or ensure that fishing practices remain sustainable.

To address this gap, a researcher from the National University of Bangladesh conducted a focused study at the Port Road Bazar, a major landing hub in the Barisal district. The goal was to create a clear, practical guide for identifying five commercially important species found in these waters: three types of freshwater prawns and two types of marine shrimp. The researcher selected one healthy, intact specimen of each species to examine in detail. By measuring specific body parts and counting the tiny spines on their heads and claws, the study established a set of physical "fingerprints" for each animal. This work does not rely on complex genetic testing but instead focuses on the visible features that a fisherman or a market inspector could use to tell the species apart.

The study successfully separated the two main groups of these crustaceans based on their body structure. The freshwater prawns, belonging to the genus Macrobrachium, were identified by the absence of a specific spine near their gills and by their most striking feature: a pair of second claws that are dramatically elongated and often asymmetrical, used for defense and mating. In contrast, the marine shrimp, from the genus Penaeus, lack these giant second claws. Instead, they possess a different arrangement of spines on their head shield and have the first three pairs of legs ending in small claws. These structural differences are consistent and reliable, allowing for a clear distinction between the river-dwelling prawns and the sea-dwelling shrimp.

Within the group of freshwater prawns, the researcher found that the number and arrangement of spines on the rostrum—the pointed, beak-like projection between the eyes—provided a consistent way to tell the three species apart. One species, locally known as the Chikna Chingri, had a specific count of spines on the top and bottom of this projection. A second, the Galda Chingri, showed a different, denser pattern of spines, while the third, the Lona Icha, displayed yet another unique combination. The study also recorded the physical size of each specimen, noting that the Lona Icha was the largest, measuring 16.5 centimeters in total length, while the Galda Chingri was the smallest at 7.5 centimeters. The measurements revealed that the rostrum of the Lona Icha was exceptionally long relative to its body, a feature that helped distinguish it from the others.

The two marine shrimp species were also distinguished by their spine counts and body markings. The Green Tiger Prawn, or Shobuj Bagh Chingri, was found to have a straight, robust rostrum with spines only on the top edge, while the Giant Tiger Prawn, known locally as Bagda Chingri, had a curved rostrum with spines on both the top and bottom. The Bagda Chingri also displayed a distinct pattern of alternating yellow-green and dark-brown bands across its back, whereas the Green Tiger Prawn had a different coloration. The researcher measured the length of the body, the head shield, and the eyes for each specimen, calculating how these parts related to one another in size. For instance, the rostrum of the Green Tiger Prawn was found to be significantly longer than its head shield, a proportion that differed from the other species.

While the study provides a solid foundation for identifying these species in the field, the researcher is careful to note that the findings are based on a single specimen of each type. This means the measurements represent individual examples rather than the full range of sizes and shapes found in the entire population. The study serves as a preliminary baseline, a starting point that confirms the physical differences between these species are clear enough for field identification. The author suggests that future work should include larger numbers of specimens and genetic testing to confirm these findings and to understand how these populations vary across the delta. For now, this detailed look at the physical traits of five key species offers a practical tool for anyone working to understand and manage the rich crustacean life of the Barisal delta.