Hi Md.Tanvir Rahman !

• I am not sure if there is a commercially available fish pathogen detection kit, but I have experience using LAMP assays and they are quite reliable (as long as you ensure no false positives).
• There are many colorimetric LAMP assays (using dyes like Calcein, phenol red, etc) that do not rely on expensive lab equipment like PCR available to be used. Making results easier to be visualized.
• These LAMP assays are high specific and can easily be validated through specificity experimentation by cross referencing against your target pathogen and non target pathogens. I would suggest that you also carry out sensitivity test through serial dilution to identify how sensitive your assay will be!
• Overall, I would highly recommend using LAMP assays as an alternative to PCR.
• Here are some resources that I found that can be beneficial for your reference.

Article Detection of Vibrio anguillarum and Vibrio alginolyticus by ...

Article Rapid detection of tilapia lake virus using a one-step rever...

Article Rapid in-situ detection kit (RisK): Development of loop-medi...

Article Loop-mediated isothermal amplification as an emerging techno...

I hope this helps.

Lavan.

Dear Sir, recently some rapid test kid has been developed to detect fish pathogens on spot. The following test kits are regularly using by researchers as well as by the fish farmers for instance, LAMP assays, immunochromatographic test strip, recombinase polymerase amplification (RPA) etc. Here I am also providing some links where you will be able to read some interesting research articles. Best

Article Diagnostic validation of a rapid and field-applicable PCR-la...

Article An immunochromatographic test strip for rapid detection of f...