Multi-organ histological assessment of Agrococcus sp. RKDAS_1 reveals tissue-level biocompatibility in Oreochromis...

A histological safety profile is essential for non-antibiotic microbial interventions in aquaculture. This study assessed the multi-organ histological biocompatibility of a novel actinobacterial strain, Agrococcus sp. RKDAS_1, in Nile tilapia (Oreochromis niloticus) under controlled conditions. Juvenile tilapia were fed diets with varying concentrations of RKDAS_1 (10⁵, 10⁷, and 10⁹ CFU g^{- 1} feed) for 60 days. Tissues from the gill, intestine, liver, and heart were analysed through standard histological methods, employing semiquantitative scoring and intestinal morphometry. Across all examined organs, RKDAS_1 supplementation did not induce inflammatory responses, degenerative lesions, or structural disruptions, which are indicative of tissue-level toxicity. Gill architecture was intact, with normal hepatocyte arrangements and no necrosis or fibrosis, while cardiac tissues showed a normal structure. Intestinal morphology maintained epithelial integrity, displaying dose-related variations in villus height and goblet cell density. Intermediate-dose live hepatic sections showed reduced cytoplasmic vacuolation compared to controls, though the difference was not statistically significant. The semi-quantitative histopathological evaluation showed that the tissue structure remained intact across different treatments. The results collectively suggest that Agrococcus sp. RKDAS_1 did not cause any noticeable histopathological damage, indicating enhanced biocompatibility. The findings suggest that Agrococcus sp. RKDAS_1 is compatible with biological tissues without causing significant damage. However, these conclusions are restricted to structural analysis and do not ensure functional improvements or overall safety beyond tissue examination. The findings provide a critical starting point for future research, which will delve into molecular, immunological, and long-term exposure studies. These investigations aim to evaluate the biotherapeutic potential of RKDAS_1 thoroughly.