In the era of industrial agriculture, agrochemicals have become a global necessity to increase the productivity of crops and fields (Vajargah et al., 2013). As a result, one of the biggest problems we face is pollution from chemicals used in the agricultural industry, which have a strong impact on the aquatic ecosystem (Dar et al. 2022; Curpan et al. 2022) (Vajargah et al. 2021). Among the most widely used pesticides (Blahova et al. 2020) of the past centuries, glyphosate certainly stands out due to its massive use in recent times. Because of its intensive use as a chemical herbicide to control weeds has become a dominant feature of industrial agriculture and, consequently, a major environmental and health concern. Environmentally because of its wider effects on biodiversity, water, and soils (Sehonova et al. 2018; Stara et al. 2019). From a health perspective because of the possible consequences of overexposure and toxic residues in food for consumption. Growing public concern about the consequences of the massive use of this herbicide in industrial agriculture has been stemmed by many governments, who consider glyphosate to be much safer than other substances with the same intent and use (Hasaneen 2012).
Glyphosate (N-phosphonomethyl Glycine) is a broad-spectrum non-selective organophosphorus herbicide. Its chemical characteristics allow it to distribute throughout the plant to kill its meristems after a few days, making it extremely effective in controlling perennial weeds (Duke 2018). Glyphosate alone is not used as a herbicide; it is always blended with different surfactants to increase its effect. The most widely used glyphosate-based herbicide today is Roundup® (Roundup 41% SL, Bayer AG, Leverkusen, Germania), which contains polyoxyethylene amine (POEA), which is a surfactant useful for improving the absorption and translocation of the active ingredient in the plant (van Bruggen et al. 2018). To date, it is possible to say that a close correlation and dependence have been established between high-yielding orchards and herbicides, as they are an essential component of plant survival and weed control. However, the herbicides that can be chosen in Iran for weed control are very limited. Currently, there are mainly two types of herbicides to choose from glyphosate and paraquat. (Meza-Joya et al. 2013; Lugowska 2018).
Because Roundup can easily reach aquatic ecosystems by runoff, drainage, leaching, it represents a hazardous and widely distributed environmental contaminant. Toxic effects involve different aspects of the aquatic organism and are not limited only to death, but also extend to alterations in their metabolism (Costa et al. 2008), growth (Fiorino et al. 2018a)h, alterations in haematological parameters (Cavas and Konen 2007), histopathological changes(Yalsuyi et al. 2021a), and of course behavioural changes (Giesy et al. 2000; Peixoto 2005; Kelly et al. 2010; Romano et al. 2012).
The massive increase in the use of glyphosate since the 1970s has led governments in several countries to take action in recent years to try to reduce or ban its use. Spain, Italy, Germany, Canada, Portugal, and the Netherlands have already reduced or banned glyphosate. The majority of glyphosate restrictions or bans worldwide were introduced after the 2015 IARC report on glyphosate found that glyphosate is a "probable human carcinogen" (Baum 2019; Klingelhöfer et al. 2021).
During these years, numerous studies have been conducted to assess the effects of this herbicide on different animal populations(Fiorino et al., 2018; Yalsuyi et al., 2021). Toxic effects of glyphosate were also studied on different classes of vertebrates. The majority of past ecotoxicology studies have confirmed that fish is a good model for assessing the toxicity of a substance in the aquatic system, due to their ability to metabolise xenobiotics, their sensitivity to contaminants, and their position in the aquatic food chain(Fazio et al., 2014; Lauriano et al., 2016; Vajargah et al., 2018; Vajargah and Hedayati., 2017; Yalsuyi et al.,2017).
Glyphosate has shown its toxic effects on many invertebrates found both on land and in water. For example, this herbicide was tested on Daphnia magna, and it turned out that both glyphosate and its common formulation. The commercial formulation Roundup is toxic to these aquatic organisms (Cuhra et al., 2013). In Cherax quadricarinatus, the freshwater crayfish (Frontera et al., 2011), exposure to this herbicide resulted in reduced somatic cell growth, muscle glycogen, lipid reserves, and muscle protein levels. (Gill et al. 2018).
The effects of glyphosate were studied by Nešković et al. on freshwater carp (Cyprinus carpio L.). Toxicity tests were carried out by exposing the animals to three different concentrations of glyphosate (2.5, 5 and 10 mg/L) and showed that the herbicide is mildly toxic to carp. In this regard, the research team found biochemical evidence of increased alkaline phosphatase activity in the fish liver at all concentrations. Histopathological studies showed cases of epithelial hyperplasia and sub-epithelial oedema at both intermediate and higher concentrations. In addition, there is leucocyte infiltration, hypertrophy of chloride cells, and lifting and rupture of the respiratory epithelium (Nešković et al. 1996).
Another interesting study by Cattaneo et al. tested Roundup in Cyprinus carpio, evaluating its effect on acetylcholinesterase enzyme activity and oxidative stress. Five different concentrations of the herbicide (0, 0.5, 2.5, 5 and 10 mg/L) were chosen to conduct the study. The study revealed repression of acetylcholinesterase activity in the brain and muscle. Furthermore, lipid peroxidation and anti-acetylcholinesterase action stimulated by Roundup on fish was confirmed (Cattaneo et al. 2011).
The research group of Webster and Santos investigated the toxic effects of glyphosate and Roundup on brown trout (Salmo trutta). Again, the animals were exposed to three different concentrations (0, 0.01, 0.5 and 10 mg/L) of pollutants. The study showed that both glyphosate and Roundup cause changes in the control mechanisms for the cellular stress response, in particular apoptosis. Furthermore, both pollutants increase cell proliferation, cell turnover and lead to an up-regulation of metabolic processes (Uren Webster and Santos 2015).
The present study aimed to evaluate the toxic effects of exposure to the commercial formulation of glyphosate (Roundup 41% SL, Bayer AG, Leverkusen, Germany) in grass carp (Ctenopharyngodon idella). Four increasing concentrations of glyphosate were chosen for the 96-hour experiment. The mortality rate, tissue damage and blood parameters were evaluated for the experiment.