Comparison of the sensitivity of different fish species to medical substances.

OBJECTIVES: Formaldehyde, sodium chloride and potassium permanganate belong to the commonly used substances for fish treatment. The aim is to define and compare their acute toxicity and therapeutic index between two fish species - Danio rerio and Poecilia reticulata.

DESIGN: To determine acute toxicity of these compounds, the semistatic method was implemented in compliance with the OECD No. 203 (Fish acute toxicity test). In each test series, 4 acute toxicity tests were performed. The results were subjected to the probit analysis to determine the 96hLC50 values. Therapeutic index (TI) was calculated with respect to short-term LC50 and effective therapeutic concentrations commonly used for fish treatment.

RESULTS: The mean 96hLC50 values for sodium chloride were 21.69 +/- 0.92 g l-1 (TI = 1.4) for P. reticulata and 10.39 +/- 0.12 g l-1 (TI = 1.0) for D. rerio. The acute toxicity of formaldehyde for D. rerio expressed as 96LC50 was 0.12 +/- 0.003 ml l-1 (TI = 5.24) and for P. reticulata 0.1 +/- 0.003 ml l-1 (TI = 4.9). The acute toxicity of potassium permanganate for D. rerio expressed as 96LC50 was 1.25 +/- 0.15 mg l-1(TI = 1.5) and for P. reticulata 1.43 +/- 0.05 mg l-1 (TI = 2).

CONCLUSION: P. reticulata showed significantly higher (p < 0.05) tolerance to sodium chloride than D. rerio, whereas D. rerio showed significantly higher (p < 0.05) tolerance to formaldehyde than P. reticulata. The acute toxicity of potassium permanganate was comparable for both fish species. Calculated therapeutic indexes of all tested substances were low; therefore it is important to conduct preliminary tolerance tests before application of treatment baths.