Fishes

This review is part of a series of studies on short-lived radionuclide accumulation in aquatic organisms following nuclear weapons testing, routine facility discharges, and accidental releases. It examines the pathways of uptake, accumulation, and internal redistribution of ¹²⁵Sb, ¹³¹I, ¹⁴¹Ce, and ¹⁴⁴Ce in fish representing different ecological groups. The analysis combines published literature data with our original findings obtained from studies conducted in the cooling pond of the Chornobyl Nuclear Power Plant and the Kaniv Reservoir during the post-accident period. It has been established that radionuclide accumulation is governed by their physicochemical properties, environmental speciation, and the trophic characteristics of fish. ¹²⁵Sb demonstrates high bioavailability and accumulates in internal organs, gills, roe, and muscle depending on its chemical form in the aquatic environment. ¹³¹I is characterized by high solubility, rapid incorporation into biological processes, and transient retention in tissues. ¹⁴¹Ce and ¹⁴⁴Ce exhibit low mobility, strong association with particulate matter, and preferential accumulation in the gastrointestinal tract, external, and mineralized tissues. At the same time, the presence of ¹⁴⁴Ce in the muscle tissue of carnivores and piscivores suggests possible trophic transfer and does not exclude potential manifestations of limited biomagnification of this radionuclide under conditions of elevated environmental contamination. It has been determined that the ratio of ¹²⁵Sb to ¹⁴⁴Ce can be used to identify contamination sources: their co-occurrence is interpreted as evidence of fuel particle input, explaining their predominant localization in the gastrointestinal tract and, to a lesser extent, in external tissues. Conversely, their separate detection reflects differences in mobility and bioavailability. It has been shown that the principal pathways for the uptake of the investigated radionuclides by fish are particle ingestion and absorption from the dissolved phase; thus, trophic dilution predominates over biomagnification, although trophic transfer of ¹⁴⁴Ce cannot be excluded.

This study evaluated the anti-virulence effect of AuraAqua (Aq), a natural mixture of organic acids, against Pseudomonas. fluorescens. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Aq against P. fluorescens were 0.5% and 1% (v/v), respectively. Growth curve analysis confirmed concentration-dependent inhibition of planktonic growth, while sub-inhibitory Aq (0.25%; 1/2 MIC) significantly reduced biofilm formation. Rhodamine-based assays revealed membrane depolarisation at both 0.25% and 0.5% Aq, with decreased intracellular protein levels, indicating impaired membrane integrity under the tested conditions. In fibronectin adherence assays, the presence of Aq during bacterial contact markedly reduced adherence, whereas short pre-treatment alone produced limited, non-persistent effects, suggesting that continuous exposure is required to interfere with host matrix binding. Supernatants and lysates from Aq-exposed P. fluorescens induced lower extracellular protease activity in a concentration-dependent manner and mitigated P. fluorescens-induced cytotoxicity in primary shrimp (SGP) and tilapia (TGP) gut cells, as measured by lactate dehydrogenase (LDH) release after exposure to bacterial supernatants and lysates. Aq treatment was associated with decreased P. fluorescens internalisation into SGP and TGP cells. Collectively, these data show that Aq exerts multi-target inhibitory and virulence-attenuating effects on P. fluorescens, supporting its potential use in aquaculture environments.

The black shinner Pseudopungtungia nigra is an endangered freshwater fish endemic to Korea, and standardized anesthetic protocols are needed for conservation-related hatchery handling. This study evaluated the effects of water temperature and MS-222 concentration on anesthetic induction and recovery responses in hatchery-reared juvenile P. nigra of approximately 3 cm total length. Juveniles were exposed to four MS-222 concentrations, 80, 100, 150, and 200 mg L⁻¹, at three water temperatures, 21, 24, and 27 °C. Induction time, recovery time, and recovery success within 600 s were assessed using behavioral endpoints. The 80 mg L⁻¹ treatment induced anesthesia within 600 s only at 27 °C, whereas fish exposed at 21 and 24 °C failed to reach the defined anesthetic stage within 600 s; therefore, this treatment was treated as a low-concentration induction-failure condition. In the main 3 × 3 factorial analysis using 100, 150, and 200 mg L⁻¹, induction time decreased significantly with increasing MS-222 concentration and water temperature, with significant effects of temperature, concentration, and their interaction. In contrast, recovery time increased with increasing MS-222 concentration, indicating a clear trade-off between rapid induction and recovery stability. Although 200 mg L⁻¹ produced the shortest induction times, it also resulted in the longest recovery times and delayed recovery at 24 and 27 °C. The 100 mg L⁻¹ treatment showed stable recovery but required prolonged induction, especially at lower temperatures. Overall, 150 mg L⁻¹ provided the most balanced behavioral response by substantially reducing induction time compared with 100 mg L⁻¹ while avoiding the greater recovery burden observed at 200 mg L⁻¹. These findings suggest that 150 mg L⁻¹ MS-222 is a practical concentration for routine short-term handling of hatchery-reared juvenile P. nigra under the tested temperature and handling conditions. However, this recommendation should be interpreted as a behavioral handling guideline because physiological stress responses and long-term post-anesthetic outcomes were not evaluated.