Length-Weight Relationship, Abundance and Sex Ratio of the Giant River Prawn Macrobrachium vollenhovenii (Herklots, 1857) From River Osun, Southwestern Nigeria

Distribution, abundance, length-weight relationships of the African giant prawn (Macrobrachium Vollenhovenii) in River Osun was studied. Four hundred and fifty (450) samples were collected at 45 per week for 10 weeks between April and June 2016, at two different landing sites (Atan and Asejire Lake). Morphometric analysis showed that the prawn exhibited positive allometric growth (L-W) with regression equation “b” values of 4.869, 6.627 and 6.205 in Atan, Asejire and pooled samples respectively. The correlation between L-W was high; r=0.580, 0.834 and 0.752 in Atan, Asejire and pooled samples respectively (p<0.05). The sex ratio of M. vollenhovenii examined showed female dominance over male with ratio of 1.57:1.00 in Atan, 1.78:1.00 in Asejire and 1.74:1.00 in pooled samples. The rostral spines on the dorsal side of M. vollenhovenii observed ranged between 11-15 while on the ventral side was between 2 and 7. The condition factors obtained in Atan, Asejire and pooled samples are 2.09, 1.58 and 1.667 respectively. The length-weight relationships of M. vollenhovenii show relationships between lengths and weights which get plumper as they grow longer. The correlation coefficient “r” indicated high correlation between length and weight. The samples were in good condition throughout the study period to depict that the environment as suitable for this prawn production.