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.
Noncontact fish body mass estimation requires accurate body extraction and reliable physical scale under changing underwater observations. This study develops a measurement-oriented instance segmentation and selective stereo-measurement method for large yellow croaker (Larimichthys crocea), centered on fin-excluded projected body area. The model combines coordinate attention, area-aware consistency loss and area-bias-guided boundary loss within Mask2Former. The stereo workflow integrates visual measurability, geometry, depth and temporal checks before track-segment aggregation. Among three phenotype regressions fitted to 104 reference fish, the area model achieved the lowest leave-one-out mean absolute percentage error (MAPE) of 6.03%. On the same 74 measurable ground-truth test instances, mask-area MAPE decreased from 1.7417% to 1.3679%, a 21.46% reduction; segmentation average precision increased from 0.769 to 0.791. Across four videos, the complete model produced an area-based segment-averaged mass of 106.60 g against a reference cohort mean of 114.04 g. Absolute mean bias decreased from 8.14% for Mask2Former to 6.52%, with observation acceptance changing from 13.83% to 6.43%. The method connects measurement-oriented segmentation to quality-screened phenotype and mass estimates evaluated through reference regression, matched mask areas and video cohort-mean comparison.
Grouper is the primary mariculture fish species in China, yet it is currently plagued by severe bacterial diseases caused by Vibrio harveyi and Photobacterium damselae. To characterize the phylogenetic relationships of V. harveyi- and P. damselae-derived cultured grouper on Hainan Island, Twenty-eight isolates (17 V. harveyi and 11 P. damselae) were recovered from moribund leopard coral grouper (Plectropomus leopardus) and hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus) sampled across farming areas during 2024–2025. Isolates were identified by 16S rRNA gene sequencing, compared with GenBank reference strains, and analyzed using neighbor-joining phylogenies. V. harveyi isolates occurred on multiple branches and were interspersed with reference strains from other Chinese regions. In contrast, 10 of the 11 P. damselae isolates from Hainan grouped within a major clade. Among the sampled isolates, neither species showed an immediately apparent spatial or seasonal pattern in its distribution across the 16S rRNA gene-based phylogenetic trees. However, the limited sampling and discriminatory power of the 16S rRNA gene do not support definitive conclusions regarding geographic or seasonal structuring. These findings provide preliminary information on the phylogenetic relationships of bacterial isolates associated with cultured groupers in Hainan and may inform future pathogen surveillance. Further studies using broader sampling and higher-resolution molecular approaches are needed to clarify the genetic relationships among these isolates.
Postbiotics are promising tools for improving shrimp production and health, but the effects of their direct application to culture water, particularly in biofloc technology (BFT) systems, remain poorly understood. This study evaluated the effects of commercial probiotic and postbiotic products on the performance of Pacific white shrimp (Penaeus vannamei) juveniles reared in a BFT nursery system. A total of 900 post-larvae (PL; initial weight: 13.00 ± 4.00 mg) were stocked in 12 experimental units for 32 days (75 PL unit−1). The experiment followed a completely randomized design with four experimental groups and three replicates: Control (without probiotic or postbiotic supplementation), Probiotic (0.5 mg L−1 day−1 probiotic powder), Postbiotic 1 (1.0 mg L−1 day−1), and Postbiotic 2 (2.0 mg L−1 day−1). At the end of the trial, shrimp reared with Postbiotic 2 supplementation had lower settleable solids concentrations than the control. Postbiotic 2 treatment resulted in higher final weight, lower apparent feed conversion ratio (FCR), and a higher Scaled Mass Index (SMI). In addition, shrimp from both postbiotic treatments exhibited greater antenna length and a higher proportion of granulocytes, suggesting changes in body condition and hemocyte composition, respectively. These findings suggest that postbiotic supplementation, particularly at 2 mg L−1 day−1, can contribute to settleable solids management and improve nursery growth performance and feed utilization in BFT systems.
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 blaTEM (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.
