Oswald Kouassi KRA¹, Fernique Kouadio KONAN^2,, Maxime Kouao DIANE², Moussa CISSE¹, Allassane OUATTARA¹, Guessennd Kouadio Nathalie²

Tilapia aquaculture (Oreochromis niloticus) is an important sector for food security in Côte d’Ivoire, but faces increasing sanitary risks from bacterial infections. This study aimed to characterize cultivable opportunistic bacteria isolated from rearing water and fish organs (skin, intestine, liver, and kidney) in semi-intensive aquaculture systems in Anyama and Aboisso, and to examine seasonal patterns in their abundance and distribution. Water and fish samples were collected during the dry and rainy seasons. Bacterial isolation was performed using conventional culture-based methods on selective and differential media, followed by identification using MALDI-TOF mass spectrometry. The diversity of cultivable isolates was assessed using the Shannon index (H′), and non-parametric statistical tests were applied to evaluate seasonal variation. Three cultivable opportunistic bacterial species were identified: Pseudomonas aeruginosa, Staphylococcus aureus, and Macrococcus caseolyticus. No significant seasonal difference was observed in the diversity index across the studied matrices. These results indicate relative temporal stability in the distribution of the recovered cultivable bacterial isolates under the present study conditions. However, because the study relied on targeted fish sampling and culture-dependent methods, the findings should be interpreted with caution and limited to the cultivable fraction of opportunistic bacteria, which may not reflect the full microbial diversity of aquaculture systems. To cultivable opportunistic bacteria. This work provides baseline data for microbiological monitoring of tilapia aquaculture systems in southern Côte d’Ivoire.

Aquaculture, Nile tilapia, cultivable bacteria, opportunistic bacteria, MALDI-TOF, seasonal variation