Identification of species plays a key role for the behavioural study. Different methods are used for identification but metric counts and morphometry are considered as earliest and authentic methods for the identification of species (Naymann, 1966). Meristic counts mean anything that can be counted while morphometry is the external measurement of an organism (Talwar and Jhingran, 1992). Morphological characters have been commonly used in fisheries biology to measure discreteness and relationships among various taxonomic categories.
The Phenotypic characterisation and natural diet of Chrysichthys nigrodigitatus in Epe lagoon were investigated between March and September 2017. The major fishing methods employed for collecting the 124 specimens were cast netting and set netting. The total lengths ranged from 15.00 to 36.3 cm (mean size 26.186 ± 0.3744 cm) while the standard lengths ranged from 10.9 to 29.4 cm (mean size 19.841 ± 0.316+1 cm). The length-weight relationship was described by the equation: Log W = a + b Log TL. The value of the coefficient of regression 'b' for this species was nearly 3 thus, indicating isometric growth. The mean condition factors ranged from 0.68 to 0.79. The food organisms consisted of phytoplankton, crustaceans, molluscs, plants material and fish parts.
The population of males was significantly (p < 0.05) higher than females in the lagoon.