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Dear Dr Mabrok

It is always preferable to conduct an LC50 experiment on the fish before conducting a challenge study. To arrive at an effective dose for bath challenge, based on the work done by other researchers, is difficult. This is because their experimental conditions may be at deviation from your's in a lot of different ways.

Following are few references about how to conduct LC50 studies on fish:

Gora, A. H., Sahu, N. P., Sahoo, S., Rehman, S., Dar, S. A., Ahmad, I., & Agarwal, D. (2018). Effect of dietary Sargassum wightii and its fucoidan-rich extract on growth, immunity, disease resistance and antimicrobial peptide gene expression in Labeo rohita. International Aquatic Research, 1-17.

Hamilton MA, Russo RC, Thurston RV (1977) Trimmed Spearman-Karber method for estimating median lethal concentrations in toxicity bioassays. Environ Sci Technol 11:714–719. https://doi.org/10.1021/es60130a004.

Other research which you may find useful :

Balfry, S. K., Shariff, M., & Iwama, G. K. (1997). Strain differences in non-specific immunity of tilapia Oreochromis niloticus following challenge with Vibrio parahaemolyticus. Diseases of aquatic organisms, 30(1), 77-80.

Barros, M. M., Falcon, D. R., de Oliveira Orsi, R., Pezzato, L. E., Fernandes Jr, A. C., Guimarães, I. G., ... & Sartori, M. M. P. (2014). Non-specific immune parameters and physiological response of Nile tilapia fed β-glucan and vitamin C for different periods and submitted to stress and bacterial challenge. Fish & shellfish immunology, 39(2), 188-195.

Lim, C., Yildirim-Aksoy, M., Li, M. H., Welker, T. L., & Klesius, P. H. (2009). Influence of dietary levels of lipid and vitamin E on growth and resistance of Nile tilapia to Streptococcus iniae challenge. Aquaculture, 298(1-2), 76-82.

regards

adnan

I following the best answer.