||The freshwater prawn, Macrobrachium macrobrachion is one of the shrimp’s species that contribute to
the fisheries in the Mono River – Coastal Lagoon water system of the Southern Benin, where major
causes of environmental degradation that affect species integrity and survival, are hydro electrical dam,
bridges, mangrove destruction, water hyacinth invasion, dumping of domestic wastes from a public
market, use of detrimental fishing gears and overfishing. A total of 780 specimens of M. macrobrachion
were sampled from two locations to investigate the morphological and taxonomic characterization of
the species and to detect whether the population is morphologically and taxonomically separable in
order to ascertain possible genetic diversity. The population exhibited significant (P≤0.01)
morphological relationships with positive slopes varying between 0.28 and 2.80 and coefficients of
correlation “r” between 0.70 and 0.96. The positive slopes “b”<3 (2.80 for Heve location; 2.71 for
Onkuiwe location) from the total length - body weight relationships suggest that M.
macrobrachion exhibited an allometric growth in the Mono River – Coastal Lagoon system. The results
indicated that the morphometric features across the two sub-populations of M. macrobrachion were not
significantly different (0.00001 ≤ F1,778 ≤ 0.205, P ≥0.05). Computed body proportions revealed that the
prawn was twice as long as its cepholothorax and twice as long as its abdomen. Also, the
cephalothorax was as long as the dorsal rostrum and twice as long as its height. The total length was
4.9-8.69 times the uropod length and 5.17-9.45 times the telson length, and the cephalothorax length
was 6-8.83 times the eye diameter. Also, the meristic counts from the two sub-populations of M.
macrobrachion were not significantly different (0.000001 ≤ F1,778 ≤ 0.000003, P ≥0.05). M.
macrobrachion had 12-15 rostral spines at the dorsal side of the rostrum and 3-5 rostral spines at the
ventral side. As a results the morphometric measurements and the meristic traits of M. macrobrachion
from the two (2) locations did not differ significantly (P≥0.05), indicating that the population of M.
macrobrachion in the Mono River – Coastal Lagoon system of Benin is morphologically and
taxonomically inseparable and, consequently, may not be genetically diversified. Hence, search in
genetic diversification requires molecular characterization to detect eventual variation among the
population. Also, for species conservation and habitat protection purpose, the output generated from
this study will form documentation for this prawn and serve as reference for species follow-up pending
any further changes in the ecosystem.