Functional specialization of probiotics for precise spotted knifejaw (Oplegnathus punctatus) farming

The spotted knifejaw ( Oplegnathus punctatus ) is an emerging high-value mariculture species, yet challenges remain with its culture due to environmental pressures and disease. Despite the widespread use of probiotics in fish culture, their application remains poorly investigated for this species. To bridge this critical gap, our study reveals, for the first time, clear functional specialization among probiotic strains that will enable precision application in the spotted knifejaw. We discovered that Clostridium butyricum CBG01 acts as a high-performance growth and intestinal health promoter, significantly enhancing growth and feeding efficiency. Its efficacy is attributed to remarkable improvements in intestinal morphology (e.g., mucosal fold height, muscularis thickness, and goblet cell density), accompanied by elevated activities of key digestive enzymes. Furthermore, C. butyricum CBG01 effectively modulated the gut microbiota by increasing beneficial bacteria and suppressing potential harmful ones. In contrast, Bacillus velezensis 26.3 and Lactobacillus plantarum W2 function as potent immune activators, comprehensively upregulating the MyD88/NF-κB pathway and antioxidant systems, indicating strong immunostimulatory properties. Notably, L. plantarum W2 built a robust and cooperative microbial ecological network, enhancing community stability and positive interactions, which aligns with its immunoregulatory role. Moreover, Bacillus subtilis BSXE-1601 demonstrated moderate benefits across multiple parameters, positioning it as a broad-spectrum regulator with intermediate efficacy. Neutral community model analysis revealed that all probiotics rendered microbial community assembly more deterministic, thereby enhancing the predictability of modulation. This functional specialization enables targeted probiotic use for knifejaw culture. For example, C. butyricum CBG01 could be used to accelerate growth during early developmental stages by enhancing intestinal health and nutrient utilization, or B. velezensis 26.3 and L. plantarum W2 could be used to enhance disease resistance during outbreaks or stressful events like transportation, owing to their immunostimulatory and microbiota-stabilizing properties. This work provides a validated, scientifically rational framework for improving productivity in spotted knifejaw aquaculture.