Lactococcus garvieae is a major bacterial pathogen responsible for lactococcosis outbreaks in aquaculture, resulting in substantial economic losses worldwide. Accurate identification of L. garvieae remains challenging because of its genetic similarity to other Lactococcus species and the limited field applicability of many existing molecular diagnostic methods. Therefore, there is an urgent need for a rapid, highly specific, and field-deployable analytical method that enables accurate identification of L. garvieae outside conventional laboratory settings. In this study, a one-pot analytical strategy integrating enzymatic recombinase amplification (ERA) with CRISPR/Cas12a detection was developed, enabling fluorescence or lateral flow dipstick (LFD) readouts within a single closed reaction tube. The one-pot ERA-CRISPR/Cas12a assays achieved a detection limit of 10 copies/reaction. When combined with a rapid DNA release protocol, qualitative detection could be completed within 50 min without the need for sophisticated instrumentation. In parallel, a TaqMan quantitative PCR assay was established as an analytical benchmark, exhibiting a detection limit of 20 copies/reaction with high linearity and good reproducibility. Clinical evaluation using 136 diseased fish samples demonstrated full concordance between the one-pot ERA-CRISPR/Cas12a and qPCR assays, with both methods achieving a positive detection rate of 23.5% (32/136). In addition, the ERA-CRISPR/Cas12a platform was successfully validated under simulated field conditions using a portable reaction device. This study presents a rapid and field-deployable CRISPR-based platform for the early detection and epidemiological surveillance of lactococcosis.

Trachinotus ovatus (golden pompano) represents one of the dominant high-value mariculture fish species farmed across coastal regions of China. In intensive farming modes, intestinal damage and immune suppression are frequent issues in golden pompano; the widespread application of antibiotics in disease control has also triggered increasing worries about ecological risks and aquatic product safety. Host-origin probiotics have been widely recognized as a green and safe strategy to mitigate health risks and promote growth in farmed fish. Nevertheless, the regulatory roles and mechanisms of autochthonous E. faecalis strains on the intestinal health of golden pompano are still poorly understood. In this study, a 42-day feeding trial was conducted using golden pompano reared in a large-capacity floating net-cage system. The experimental fish were fed diets supplemented with different concentrations of E. faecalis SZ07 (1 × 10⁵ to 1 × 10⁹ CFU/g feed). Dietary supplementation with SZ07 at suitable doses (1 × 10⁷ to 1 × 10⁸ CFU/g feed) notably improved intestinal tissue structure, elevated the activities of digestive, antioxidant, and immune enzymes, and modulated the mRNA levels of key immune genes in the spleen. Analysis of the gut microbiota revealed that dietary E. faecalis SZ07 reshaped the intestinal microbial community, with an increased abundance of beneficial taxa and a decreased proportion of opportunistic pathogens. Taken together, our results indicate that autochthonous E. faecalis SZ07 acts as an effective probiotic to enhance intestinal health and immune function of golden pompano and offers technical support for the healthy development of its aquaculture industry.