Some aspects of the biology of Macrobrachium dux (Lenz, 1910) (Crustacea: Decapoda: Natantia) ine RIver Orogodo, Niger Delta, Nigeria

Preliminary investigation into some aspects of the biology of the palaemonid prawn, Macrobrachium dux (Lenz, 1910) in River Orogodo at Abavo, southern Nigeria was carried out between March and August 1995. The freshwater prawns were collected with properly baited cage traps and scooping with hand basket. The study revealed that the prawn species were widespread and abundant in the river. Abundance in terms of number and biomass was more during the wet season with a peak in August. Both adults and juveniles showed a progressive increase from late dry season to midrainy season (August). The malefemale ratio was 1:1.2. The fluctuation in the number and percentage of ovigerous females indicated that the prawn spawned during the midrainy season (JuneAugust). Ovigerous females ranged from 4.6 to 7.5 cm and egg size varied from 1.5 to 1.7 mm. The prawn attained a maximum total length and weight of 7.5 cm and 7.0 g respectively. Its growth pattern was allometric. The mean monthly condition factor (k) ranged from 1.43 to 2.37 and generally showed a monthly fluctuation with a peak in July.