MERISTICS AND MORPHOMETRIC FEATURES OF Macrobrachium vollenhovenii (African River Prawn) FROM OVIA RIVER, NIGER DELTA, NIGERIA.

*Ehigiator, Flora.A.R. and Obi, Akolisa.
Department of fisheries, University of Benin, Benin City, Nigeria.
*Corresponding Author *farehigiator@yahoo.com
 

Introduction

Freshwater prawns of the genus, Macrobrachium (decapod crustaceans) are important for commercial fisheries and aquaculture since they provide food and revenue to many countries. Meristic and morphometric features are important in age determination, unit stock assessment, and recruitment of any prawn species into aquaculture and also useful in identification of prawn species. Growth pattern of decapod crustaceans has been studied widely. Three allometry growth patterns exist: positive allometry, (dependent variable grows fast with respect to body size); isometric and negative allometric growth (dependent variable grows slower than body size). Fish grow isometrically when the value of b = 3; values > or < 3 show that the fish exhibit allometric growth.

Methods

M. vollenhovenii caught with baited traps for two years were used for morphological studies. Total (TL), antennal (Ant) and chelal (CL) lengths measured (mm) using measuring board; carapace (CL) & rostral (RL) lengths measured using Venier Calliper. Dorsal and ventral rostral spines were counted. Body weight (BW) measured Metler balance (Model P1200W) (gm). Sexes were separated using morphological features.

Results and Discussion

Summary of morphometric and meristic features (Table 1). M. vollenhovenii exhibited positive allometric growth with "b" values of 3.42, 3.0 and 3.28 for the males (M), females (F) and combined sexes (CS) respectively. Result agrees with the results by with "b" values of 6.32 and 3.11 for M. vollenhovenii. The males were larger than the females. Correlation between Total Length and Body weight was high (r = 0.94 (M), 0.92 (F) and 0.93 (CS). A significant (p<0.05) correlation occurred between TL and CL (r = 0.95, 0.82 and 0.89 for M, F, & CS): between TL and RL with "r" values of 0.79 (M), 0.74 (F) and 0.77 (CS); between TL and Ant length (r = 0.61 (M), 0.49 (F) and 0.56 (CS).

High correlation between measurable parameters indicates that increase in TL results in increase in CL & RL length. Bigger prawns have longer antenna. Dorsally, 48% of the prawns examined had 13 spines on their rostrum while ventrally 67.8% had 4 spines. The females of predominated with sex ratio of 1:1.04 (p>0.05). Similar result was reported for M. dux.

Conclusions. High degree of correlation between measured parameters indicates that any of these variables could be used in establishing length-weight relationship in M. vollenhovenii.