Morphometric adaptation of Bobo Croaker, Pseudotolithus elongatus (Bowdich, 1825) (Sciaenidae) in the Cross-River estuary, Nigeria. – P.E. Asuquo and H.T. Ifon
This study was carried out to assess the morphological adaptation of the Bobo croaker (Pseudotolithus elongatus) in different portions of the Cross River Estuary. A total of one hundred and twenty fish specimens were collected from landings (Ikang, Nsidung, Oron and Ibaka beaches) of the artisanal fisheries from September to November, 2018. Fifteen traits including standard length, body depth/width, head and fin characteristics were measured to the nearest 0.1cm using Veneer Callipers and measuring board. Spatial data were analyzed using one-way analysis of variance (ANOVA) which showed ten significant traits between habitats. Derived discriminant functions with ten standardized morphometric traits identified nine traits as significant contributors (Wilk’s Lambda at P<0.001) among which body width (BW) contributed most (Wilks’ Lambda=0.430) while orbital length (OL) was the least (Wilk’s Lambda=0.819). The derived classification functions correctly classified up to 77.5% of original grouped cases; the remaining 22.5% could be attributed to other factors rather than morphology. While the best classification success was derived for Ibaka group (96.7%), the lowest success was for Ikang group (60%). All pair-wise Mahalanobis distance (D2) values in the different groups correlated significantly (P<0.05) to the approximate pair-wise geographic distance value. The plot of first two canonical variables (CDF I and II) was able to significantly separate the samples into four distinct groups implying morphological adaptation of P. elongatus to discrete habitats. Hence different management strategies should be used to maintain these morphologically separated stocks.