Aquaculture Journal

Aquaculture is a rapidly growing industry, with worldwide production reaching new levels. Intensive aquaculture often leads to the occurrence of bacterial diseases, which cause large economic losses. Antibiotics are the first choice for the treatment of these diseases, but their frequency or improper use results in the development of antimicrobial resistance. The aim of this study was to present the mechanisms of antimicrobial resistance to the most widely used groups of antibiotics, such as quinolones, tetracyclines, and phenicols, for controlling bacterial diseases in fish. The selective pressure exerted by these pharmaceuticals drives the emergence of resistant bacterial strains and the horizontal transfer of genes encoding this resistance. The transmission of resistant pathogens from aquaculture to other animals and humans is well documented, which complicates the treatment of emerging bacterial diseases. Hence, the aquatic environment is a major reservoir of resistant bacteria, genes, and antimicrobials. Efforts should be made to stop the excessive and improper use of antibiotics in aquaculture and encourage farmers to use alternative means for the prevention and control of bacterial diseases. Several alternative strategies can be employed in aquaculture as substitutes for antibiotics, thereby mitigating the development of antimicrobial resistance. Among the most prominent alternative measures are vaccines, immunostimulants, and bacteriophage therapy. Encouraging the adoption of sustainable farming practices plays a critical role in fostering optimal conditions for aquaculture systems, thereby mitigating disease outbreaks and obviating the need for antibiotic treatments. Antimicrobial resistance is effectively mitigated through the implementation of a holistic One Health approach, which systematically curtails the emergence and dissemination of resistant bacteria while safeguarding human and animal health.

This review synthesizes the available evidence on the effects of Hermetia illucens meal inclusion on the intestinal microbiota of fish. A literature search was conducted in Scopus, Web of Science, PubMed, and Embase from inception to 23 April 2025, including in vivo experimental studies reporting changes in fish intestinal microbiota. Of 2525 records identified, 39 studies met the predefined PICOS-based eligibility criteria and were included in a PRISMA 2020-guided synthesis; risk of bias was assessed using the SYRCLE tool. Given the substantial methodological heterogeneity among studies (fish species, dietary formulations, sequencing platforms, and analytical pipelines), no quantitative meta-analysis was performed, and results were synthesized semi-quantitatively based on the direction of reported effects. At the phylum level, most studies reported significant increases in Bacillota (41% vs. 16% decreases; n = 32) and Actinomycetota (65% increases; n = 26), while Pseudomonadota showed a recurrent, though not universal, reduction (50%; n = 28), with enrichment of genera such as Bacillus (70%; n = 20), Enterococcus (81%; n = 16), and Oceanobacillus (93%; n = 15). These changes have been hypothesized to involve prebiotic, metabolic, and antimicrobial mechanisms related to chitin, lauric acid, and antimicrobial peptides. Overall, H. illucens meal inclusion (~10–30%) appears to be associated with a predominant, though not universal, modulation of the fish intestinal microbiota toward profiles with greater fermentative and chitinolytic potential; an inference based on the ecological attributes of the enriched taxa rather than on functional measurements. The magnitude and consistency of this modulation depend on dose, species, habitat, and meal processing type.

The milky disease caused by Metschnikowia bicuspidata has severely affected the farming of Chinese mitten crabs (Eriocheir sinensis), yet there are still no effective and environmentally friendly control measures available. This study employed a drug-repositioning strategy, combined with virtual screening, in vitro antifungal tests, and in vivo experiments, to evaluate the effect of cetylpyridinium chloride (CPC) on the pathogen. Sterol 14α-demethylase (CYP51), the key enzyme in the ergosterol biosynthetic pathway, was selected as the candidate target for molecular docking. The docking results showed that CPC had a strong binding affinity (score −9 kcal/mol) to the predicted CYP51 active site, but its use as a direct target still requires further biochemical verification. In the in vitro experiment, CPC exhibited potent antifungal activity (MIC = 1.56 μg/mL, MFC = 3.125 μg/mL) and significantly reduced the formation of biofilms at the tested concentrations (p < 0.05). After feeding at a dose of 800 μg/g feed for 7 days, the activities of immune-related enzymes (ACP, AKP, LZM) and antioxidant enzymes (CAT, SOD, GPX) in the hepatopancreas of crabs significantly increased (p < 0.05), and no oxidative stress was induced. In the challenge test, the original cumulative mortality rate of group C (challenge + 800 μg/g CPC bait) was 59.72%, lower than that of group B (challenge + basal feed) at 75.00% (absolute risk reduction of 15.28 percentage points). The corrected survival rates were 40.0% (group C) and 24.4% (group B), but the group differences after correction by the generalized linear mixed model did not reach a statistically significant level (p = 0.068). The histopathological score showed that CPC significantly alleviated the severity of lesions in the hepatopancreas, gills, muscles, and heart (p < 0.001). Although the targeting mechanism of CPC against CYP51 requires further experimental validation, our findings suggest that CPC holds promise as a drug-repositioning candidate for managing milky disease in E. sinensis, particularly by boosting host immunity and mitigating tissue damage.