Calibration transfer is of great necessity for practical applications of near infrared (NIR) spectroscopy, since the original calibration model would become invalid when spectra are measured on different instruments or under different detection conditions.

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A label‐free and novel surface‐enhanced Raman scattering (SERS) method has been studied to rapidly detect common fish pathogenic bacteria (Escherichia coli, Vibrio anguillarum, Vibrio harveyi, Edwardsiella piscicida, and Pseudomonas plecoglossicida). The marriage of magnetic nanospheres (Fe3O4) with polyethylenimine (PEI) could trigger surface charge modifications of Fe3O4, making it effective to capture negatively charged bacteria. After the rapid bacterial capture procedure within 10 min, Au@Ag core‐shell bimetallic nanoparticles served as hotspot providers to facilitate the enhancement of biological Raman signals. The results demonstrated that the minimum detection limit of E. piscicida could be as low as 105 cfu/ml. The peak intensity at 1628 cm−1 (E. piscicida) showed a linear relationship with the logarithm of the bacterial concentration (R2 = 0.997). A mimic test was conducted by spiking E. piscicida into tap water. Linear discriminant analysis (LDA) was also harnessed to classify different types of fish bacteria. And the positive rates of the training set and the prediction set were 100% and 80%, respectively. The whole experimental procedure only takes 20 min. This method opens a new avenue for the rapid detection and identification of fish pathogenic bacteria.