Microplastic ingestion in the benthopelagic tank goby Glossogobius giuris is shaped by environmental exposure and ecomorphological traits.

Resident biota is often used as a proxy for microplastic (MP) contamination in aquatic ecosystems; however, species-specific ecological traits such as habitat preference, feeding strategy, and morphological and anatomical adaptations may influence MP uptake, thereby limiting the universal applicability of a single species as a bioindicator. Therefore, widely distributed species occurring across differentially contaminated aquatic ecosystems require focused evaluation. In the present study, we investigated MP ingestion in the benthopelagic tank goby Glossogobius giuris from two contrasting river systems (Bhima and Ulhas rivers) to examine how environmental exposure and ecomorphological traits together shape MP burden. MPs were isolated from gastrointestinal (GI) tracts, characterized by microscopy, and polymer identity was confirmed using Raman spectroscopy. High-resolution micro-computed tomography (μCT) was used to comprehend the structure and role of feeding-related oral and pharyngeal morphology in MPs ingestion and retention. MPs were detected in 52.94% of individuals, with higher prevalence in the Bhima River than in the Ulhas River. In total, 47 MP particles mainly fragments and films composed of polyethylene and polypropylene were recorded, indicating their origin from secondary anthropogenic sources. Biometric and life-history traits such as size, body condition, sex, or reproductive state showed no significant relationship with MP abundance. Instead, patterns of ingestion appear to reflect both habitat-associated exposure and species-specific feeding behavior, suggesting a possible role of oral structures in MPs intake. The μCT observations provide evidence for the involvement of oral and pharyngeal structures to facilitate incidental MP particle capture and short-term retention during prey acquisition. The results of the present investigation suggest that the designation of any species as a bioindicator should be undertaken with caution, as MP ingestion, retention, and egestion are highly species-specific processes governed by ecological context, trophic behaviour, and feeding-related morphology.