Fishes

Edwardsiella piscicida causes severe edwardsiellosis in farmed finfish, particularly Paralichthys olivaceus. Lacking clinical breakpoints, epidemiological cut-off values (ECVs) are crucial for distinguishing wild-type (WT) populations from non-wild-type (NWT) strains. We evaluated 68 E. piscicida isolates from South Korea (2022–2025) across six aquaculture antimicrobials. Tentative ECVs derived via Normalized Resistance Interpretation were established at 8/4 µg/mL for amoxicillin/clavulanic acid (64.7% WT), 2 µg/mL for florfenicol (92.6% WT), 0.5 µg/mL for oxytetracycline (38.2% WT), and 0.25/4.75 µg/mL for trimethoprim/sulfadiazine (51.5% WT). Due to pronounced bimodal distributions and mathematical fitting artifacts, objective ECVs could not be reliably determined for enrofloxacin and flumequine via unimodal modeling. ARG screening revealed high prevalence of bla_TEM (54.4%) and qnrS (52.9%). Tetracycline resistance genes were harbored by 60.3% of isolates (tetD, 45.6%; tetA, 7.4%; tetB, 5.9%; tetB&tetD, 1.5%; tetE, 0%), showing strong statistical concordance with the oxytetracycline NWT phenotype. Furthermore, floR (7.4%) and sul2 (14.7%) strongly correlated with florfenicol and potentiated sulfonamide NWT phenotypes, respectively. Presumptive multidrug resistance (pMDR) remained low at 4.4% (n = 3). These findings establish empirical baseline ECVs for East Asian aquaculture, supporting responsible antimicrobial stewardship and diagnostic harmonization.

Recruitment and the spatial distribution of early life stages govern the resilience of exploited elasmobranch populations, yet remain poorly understood in demersal sharks. We examined the bathymetric structure and recruitment hotspot recurrence of juvenile Galeus melastomus, a frequent by-catch of deep-water bottom trawling, in the central–southern Tyrrhenian Sea (GSA 10), using MEDITS data (2017–2024). Juveniles were defined as immature individuals (maturity stages 1–2) smaller than the sex-specific length at first maturity (L50: 384.1 mm in males, 425.1 mm in females). The Recruit Density Index (RDI, juveniles/km²) was compared among depth strata, analysed with a Tweedie generalised additive mixed model accounting for station and sampling season, and mapped by Inverse Distance Weighting; hotspot persistence was tested against random expectation. Juveniles occurred in every survey year, supporting continuous recruitment. Juvenile density was highest in the 201–500 m stratum (p < 0.001), peaking near 400 m. Densities were higher in autumn–winter surveys, and the model indicated a possible decline of about 12% per year requiring confirmation. Recruitment hotspots occurred mainly in this stratum and recurred at a small number of stations more often than expected by chance. These results can inform the monitoring and management of demersal elasmobranch by-catch in the Mediterranean Sea.

Hybrid Clarias catfish account for more than 90% of farmed catfish production in Thailand, making hatchery resilience relevant to the continuity of freshwater fish supply. This secondary-data modelling study evaluated how early-life thermal stress may propagate from biological performance to hatchery production and longer-term economic outcomes. Previously published developmental data for hybrid Clarias catfish (Clarias gariepinus × C. macrocephalus) reared at 29 °C and 32 °C were used as empirical inputs to a coupled biological and bio-economic framework comprising temperature-dependent developmental functions, deterministic hatchery calculations, and 10-year scenario projections. In the source experiment, fertilization declined from 67.7% to 59.0%, hatching from 43.4% to 26.6%, and 72 h survival from 44.9% to 0% between 29 °C and 32 °C. The model represents the 32 °C condition as a developmental mismatch in which yolk reserves approach a near-depletion threshold before the assumed functional feeding threshold is attained. Under the illustrative hatchery assumptions, the unmitigated 32 °C scenario produced no viable fry at 72 h, whereas active cooling to 29 °C preserved modelled production but added energy cost. Ten-year projections further suggest that the relative economic performance of cooling and genomic adaptation depends strongly on assumed energy-cost escalation, thermal thresholds, and annual genetic gain. These projections should therefore be interpreted as scenario analyses rather than validated forecasts. The framework identifies parameters requiring empirical calibration and provides a basis for evaluating engineering, breeding, and combined adaptation strategies for climate-resilient hatchery management.