IDENTIFICATION OF BACTERIAL AGENTS ASSOCIATED WITH MASS MORTALITIES AND THEIR ANTIMICROBIAL SUSCEPTIBILITY PROFILES IN RAINBOW TROUT (ONCORHYNCHUS MYKISS) HATCHERIES IN KÖYCEĞIZ, MUĞLA, TÜRKIYE
3. INTERNATIONAL NESSEBAR SCIENTIFIC RESEARCH AND INNOVATION, 23 - 24 Ekim 2026, cilt.1, sa.1, ss.1043-1053, (Tam Metin Bildiri)
- Yayın Türü: Bildiri / Tam Metin Bildiri
- Cilt numarası: 1
- Sayfa Sayıları: ss.1043-1053
- Van Yüzüncü Yıl Üniversitesi Adresli: Evet
Özet
This study investigated a bacteriological survey conducted in response to mass mortalities in trout hatcheries in Köyceğiz, Muğla, Türkiye, during the 2026 summer production period, focusing on isolate diversity and antimicrobial susceptibility profiles. From May to August 2026, monthly sampling was performed at three hatcheries, resulting in 12 sampling events. Samples were collected from symptomatic juvenile and broodstock fish weighing 1–3000 g; anamnestic and macroscopic findings were recorded. In total, 200 fish of different sizes and weights were sampled. External examination revealed darkening, exophthalmia, and fin erosion. Necropsy revealed hepatic hemorrhage and pallor, swollen and eroded kidneys, splenomegaly, swim bladder hemorrhage, and enteric fluid accumulation with intestinal hemorrhagic lesions. Samples were inoculated onto TSA, BHIA, TCBS and TYES agar. Following purification, DNA was extracted from isolated colonies and the 16S rRNA gene region was sequenced. Sequences were compared using NCBI BLAST. Antimicrobial susceptibility was evaluated by the Kirby–Bauer disk diffusion method according to CLSI standards. The isolates were identified as Lactococcus garvieae (98.48%, PQ895638.1; 98.68%, AP043894.1; 98.54%, CP160834.1; 98.70%, CP160834.1), Peribacillus sp. (99.60%, PZ492163.1), Aeromonas sobria (98.54%, DQ625324.1; 96.73%, PX617742.1), Pseudomonas sp. (97.61%, DZ409873.1), Pseudomonas fluorescens (99.46%, CP169220.1), Pseudomonas brenneri (99.46%, MF838684.1), Microbacterium phyllosphaerae (99.45%, OZ336857.1), and uncultured Bacillus sp. Marked differences were observed in antibiogram profiles. The first two isolates showed broad antimicrobial susceptibility, whereas the remaining isolates exhibited varying resistance and intermediate susceptibility, particularly to amoxicillin, erythromycin, lincomycin, oxytetracycline, florfenicol, and sulfamethoxazole–trimethoprim. Gentamicin and enrofloxacin were effective against most isolates. These findings indicate that multiple bacterial agents may contribute to mass mortalities and that treatment should be guided by pathogen-specific antibiogram results.