I think you are very much unaware of the antibiotic crisis, otherwise you would not have asked this question. Another very important to mention is that, there is a very basis microbiological lab practice viz antimicrobial susceptibility testing, to determine right concentration of antibiotic against any specific pathogen. So, in any context your question seems to be illogical.

Sure,no

the concentration of A.B. different according to disease condition(stage of diseas, causative agent) fish condition ,so y should make A.B. sensitivity test

Thank you for the queries, and about the answer, please follow the answers from Shahbaa Khalil and Abhijit Singh. For treatment it should be aware about the fish species, disease, condition, cause of the disease, size of the fish stages of the fish and disease etc. Suggestion may be the consultation with aquaculture disease/parasite expert or veterinary doctor/technicians.. Thank you.

Thanks for the answers,