Sexual dimorphism in black jaw tiliapia (Sarotherodon melanotheron) and banded jewelfish (Hemichromis fasciatus) from the Great Kwa River, Calabar, Nigeria

Abstract

In this study, the pattern and magnitude of sexual dimorphic differences have been investigated in black jaw tilapia (Sarotherodon melanotheron) (n = 160; 74 males and 86 females) and banded jewelfish (Hemichromis fasciatus) (n = 120; 42 males and 78 females) from the Great Kwa River, Calabar, Nigeria. Fish samples were collected between July and December 2015. Fourteen morphometric variables, including body weight, total length, standard length, body depth, cheek depth, pre-orbital length, postorbital length, pectoral fin length (right and left), pelvic fin length (right and left), head length, gonad weight, eye diameter and four meristic variables, including number of pectoral fins (right and left) and number of pelvic fins (right and left), were taken using standard methods. Size-adjusted morphometric measurements subjected to step-wise discriminant function analysis were used to determine predictor variables to morphologically differentiate sexes for both species; magnitude of dimorphism between sexes was estimated using percentage classification accuracy of the discriminant function analysis. From the discriminant function analysis, the pectoral fin length and gonad weight positively contributed significantly to morphometric dimorphism (magnitude=69.2%) in male and female S. melanotheron suggesting adaptation for reproductive function; while for H. fasciatus the body depth and standard length were important contributors to sexual dimorphism (magnitude=84.2%) suggesting size dimorphism for aggressiveness, territorial behavior and improving swimming performance. Overall, our results indicate that the different magnitude of sexual dimorphism between the two species could be attributable to the type and functional role of sexual dimorphic traits.

Morphological Differences and Trophic Niche Breadth of Sarotherodon galilaeus and Oreochromis niloticus from the Freshwater Lake Geriyo, North-Eastern Nigeria

“…The fundamental niche of a species can be defined as the set of abiotic environmental conditions within which a species can survive and maintain viable populations (Degerman et al, 2007;Holomuzki et al, 2010;Ibor et al, 2017). Since the survival of organisms is a function of their ability to adapt to each or a combination of these interacting factors, the prevailing features of a habitat, including their environmental conditions, will determine phenotypic attributes of organisms by filtering specific traits (Hart, 1993;Silva et al, 2014;Welsh, 2013).…”

“…Trait-based studies have been used to understand how resources are partitioned between species in a community and have also been used to simplify ecological models in speciesrich communities (Corrêa et al, 2011;Yang et al, 2015). The use of morphological traits to predict ecological relationships between body form and niche function have been explored and documented for various vertebrate groups, including some freshwater fish species (Davis et al, 2012;Watson and Balon, 1984;Ibor et al, 2017;Carroll et al, 2004;Hjelm et al, 2003). This is because morphological features and patterns of development have been shown to be highly conserved within some clades (Finnegan, 2017).…”