Seasonal Diet, Composition and Feeding Pattern of Grey Mullet, Mugil cephalus in Iko River Estuary

Abstract

The diet composition and feeding activity of grey mullet (Mugil cephalus) were assessed in the Iko River Estuary, Nigeria, from August 2024 to July 2025. Specimens obtained from landed fish catches were preserved and examined for stomach contents. Dietary items were assessed using frequency of occurrence, numerical abundance and the point method, with the Index of Relative Importance used to compare their contributions. Feeding activity was evaluated using the Gut Repletion Index. A total of 1,200 fish were examined, of which 1,086 had non-empty stomachs. Twelve dietary categories were recorded, including detritus, algae, animal-derived material, plant fragments and sand. Across the pooled food-item counts, detritus was the largest category, with 888 occurrences (22.90%), followed by green algae with 643 (16.58%) and diatoms with 500 (12.89%). Seasonal Index of Relative Importance values indicated a greater relative contribution from detritus and green algae during the dry season than during the wet season. Crustacean larvae and fish parts contributed more during the wet season. Overall feeding activity was high, with a Gut Repletion Index of 90.50%. The corresponding values were 86.80% for the dry season and 93.14% for the wet season. The coexistence of detrital, algal and animal-derived food categories supports classification of the observed feeding pattern as omnivorous with a pronounced detrital component.