Fish are excellent biological models to be used in the environmental monitoring of polluted and unpolluted aquatic environments (Damato and Barbieri, 2012). In addition, they can be found in most aquatic environments, playing an important ecological role in food chains (Cort and Ghisi 2014; Barbieri et al. 2018).
Fish of the Astyanax and Deuterodon genera, popularly known as lambaris, have excellent potential as a bioindicator because they are very common, small, omnivorous specimens with considerable economic value; and are beginning to be used in several studies for biomonitoring and bioassays in Brazil (Cort and Ghisi 2014).
In the present study, it was observed that D. iguape was a good biological model, responding well as a bioindicator, corroborating with other studies that also used lambaris to study lethal and sublethal effects of pesticides (Erbe et al. 2010; Bueno-Krawczyk et al. 2015; Galvan et al. 2016) and effects of other pollutants such as gasoline (Galvan et al. 2016) and carbofuran (Barbieri et al. 2019). Therefore, due to its availability and mainly its sensitivity to small changes in the aquatic environment that resulted in measurable changes, this fish can be used in Brazil as a biological model in biomonitoring studies and bioassays with pesticides.
According to Arias et al. (2007), in recent years, aquatic biota is constantly exposed to a large number of toxic substances released daily in open environments, without proper treatment, from different sources of emission. Among the pollutants present in the water are fungicides, such as propiconazole. These fungicides can cause mortality and alterations in the metabolism of fish, as observed in the results obtained in this study with tests carried out with lambari D. iguape and zebrafish D. rerio, examining toxicity (LC50), specific oxygen consumption and ammonia excretion. It is common for fish and other aquatic organisms to be subject to receiving water contaminated by pesticides because they are close to vegetable cultivation fields treated with these substances (Hernández-Moreno et al. 2011; Cobas et al. 2016).
The toxicity of propiconazole to fish has not been well documented, especially for D. iguape and D. rerio. For example, Hemalatha et al. (2016) obtained the 96-h LC50 of propiconazole for the fish Labeo rohita at 8.9 µl L− 1; a toxicity value much higher than those recorded in the present study where the LC50 for D. iguape and D. rerio were 0.05 µg L− 1 and 0.03 µg L− 1, respectively. Wilfriel (2005) recorded 96-h LC50 values of propiconazole for various fish between 5.3 and 6.8 mg L− 1, (Oncorhynchus mykiss 5.3 mg L− 1, Cyprinus carpio 6.8 mg L− 1 and Lepomis macrochiurus 6.4 mg L− 1).
Hernández-Moreno et al. (2011) argue that there is a great variability in the results of LC50 found for different species and even within the same species, therefore, comparisons of results should be interpreted with caution to avoid erroneous conclusions possibly due to the applied test, the testing conditions, stage of life of the exposed organisms, among other factors. However, the fact is that concentrations found in the environment of 12.90 mg L− 1 can be very harmful to fish (Teng et al. 2019).
In the tests carried out with lambari and zebrafish, propiconazole, when used alone, demonstrated a significant effect in reducing the specific consumption of oxygen and the excretion of ammonia in the highest concentrations tested.
The decrease in specific oxygen consumption is closely associated with a decrease in metabolism (Barbieri et al. 2019), observed during the experiments through the low consumption of individuals exposed to higher concentrations of propiconazole compared to those exposed to lower concentrations.
This study demonstrates the action of propiconazole as a potentially toxic substance for the metabolic functions of D. iguape and D. rerio fish. It was observed that the specific oxygen consumption and ammonia excretion decreased at the highest concentration (0.1 µg L− 1) for both fish. This physiological response to the presence of xenobiotics is directly associated with changes in metabolism and occurs due to the fish's attempt to maintain its homeostasis (Barbieri et al. 2019). Atypical situations can stimulate protein synthesis not directly related to growth, such as stress and thermal shock, toxicity to metals, toxicity to pesticides, deprivation of nutrients, metabolic disorders, among others (Mommsent, 1998; Damato and Barbieri 2012).
According to Rand and Petrocelli (1985), fish can absorb pesticides directly from the water, and the gills are the main absorbing organ. The decrease in specific oxygen consumption is closely associated with a decrease in metabolism, a fact observed during experiments carried out through the low mobility of individuals exposed to higher concentrations of pesticides (Campos-Garcia et al. 2016). According to Vargas et al. (1991), xenobiotics affect the breathing processes of organisms by inducing them to use other sources of energy, which can be used for detoxification reactions and stabilization of metabolic patterns; which may explain the reduction in specific oxygen consumption to the extent where the concentration of propiconazole was increased.
Campos-Garcia et al. (2016), in studies conducted with tilapia (Oreochromis niloticus), obtained an increase in specific oxygen consumption in individuals subjected to high concentration of carbofuran carbonate, which resulted in an increase in the metabolic rates of fish. A similar result was recorded by Barbieri et al. (2019) studying the effects of carbofuran on lambari Astyanax ribeirae.
In the tests for ammonia excretion performed with lambari D. iguape and zebrafish Danio rerio, there was a statistically significant decrease in relation to the control when subjected to the presence of the fungicide, propiconazole, at the highest concentrations, demonstrating changes in the excretion of both fish. Barbieri and Ferreira (2011) identified changes in the excretion of ammonia in toxicity studies carried out with tilapia, O. niloticus, exposed to different concentrations of Folidol 600; which were similar to the results obtained in this study for lambaris and zebrafish exposed to propiconazole. Areechon and Plumb (1990) and Heath et al. (1993) proposed that this response probably occurs due to a possible lesion in the branchial tissue, resulting in internal hypoxia and stimulation of erythropoiesis.
According to Mommsen (1998), atypical situations can stimulate protein synthesis that are not directly related to growth, such as stress from heat shock, nutrient deprivation, metabolic disorders, metal toxicity, viral infection and others.
In freshwater fish the final residues of protein metabolism are excreted mainly in the form of ammonia and the mechanisms of this excretion are through gills and kidneys, and even in some fish species the skin can perform this function (Bombardelli and Hayashi, 2005). The results of ammonia excretion obtained from exposure to propiconazole showed a decrease in excretion rates, this fact suggests a decrease in protein metabolism as a mechanism to maintain the energy balance of fish submitted to propiconazole.