Three Morphotypes Of Macrobrachium macrobrachion (Decapoda, Palaemonidae): Preliminary Results Of Analysis Of Morphological Characters, With Particular Emphasis On The Spines Of The Rostrum

This study examined morphological variations in the population of Macrobrachium macrobrachion (Brackish water Prawn). Morphology of the rostrum is well known to be important in taxonomy of decapods as the shape and morphology varied widely within species. Comparative position of the dorsal spines (i.e spine after the apical teeth) and ventral spines on the rostral aperture of the small sized adult Macrobrachium macrobrachion was investigated. The study showed that this species belong to the category of highly variable species. Rostrum of all the specimens shared suits of characters equal or slightly longer than antennal scale, and tip which are slightly curved or occasionally strongly upward. However, observations aided with the hand lens (10 x) and running of pin along the edges of the rostrum showed small but constant specific differences in the relative position and occurrence of the first dorsal spine against that of the ventral spines. The total lengths recorded for the morphotypes were 7.62±1.11cm, 7.48±0.90cm, and 7.44±0.91cm respectively for MTI, MTII and MTIII while body weights for MTI= 4.83±3.07, MTII= 4.33±2.12, and MTIII= 4.24±1.83. Sex ratios were in the order of 1:6.296, 1:5.382, 1: 5.350 respectively for MT I, II and III in favour of the females. Proximity matrix analysis using UPGMA are Euclidean distance (similarity or dissimilarity) amongst the three groups identified. The finding open up a high feasibility in the application of the relative position of the spines on the rostrum of adult prawns to gain a better understanding of phenotypic differences in species and stocks. Keywords: Rostrum, Morphotypes; Macrobrachium macrobrachion. The Zoologist Vol. 6 2008: pp. 45-54