Directional asymmetry of otoliths of Chrysichthys nigrodigitatus (Lacepede 1803) indicator of environmental stress in the comoe river basin (Ivory Coast)

The impact of pollution on the otoliths of Chrysichthys nigrodigitatus organisms from the middle course of the Comoé River was assessed through the study of asymmetry. Quarterly sampling of 201 specimens of Chrysichthys nigrodigitatus was carried out over one year, from February 2021 to March 2022 at five sampling stations (M’Basso, Manzan, YèrèYèrè, Abradinou and Bettié). The otoliths were extracted and then measured. The Shapiro-Wilk test was performed to statistically verify the normality of the variables (weight, area, width, length and perimeter). Asymmetry was assessed through the AF1 and AF2 indices. After this assessment, analysis of variance (ANOVA) and the Tukey-Kramer post-hoc test were used to test for differences in directional asymmetry between sites. Directional asymmetry values varied significantly between sampling sites. Otolith analysis revealed marked directional asymmetry, predominantly oriented toward the right side. The Manzan, Bettié, Abradinou, and YèrèYèrè stations displayed the highest average directional asymmetry, while M'Basso recorded the lowest values.