It is widely accepted that the use of herbicides has increased significantly the crop yield. However, following the increasing use of herbicides in modern agriculture, a large proportion of these herbicides are accumulated in surface waters through surface runoff, leaching and drift, and is associated with environmental hazards for aquatic organisms and human health (Jiang et al. 2016; Suchiang 2021). Changes in the chemical composition of aquatic environments and exposure of fish to pesticides result in behavioral disorders, physiological disorders, histopathological injuries, hematological alterations, biochemical changes, suppression of the immune system, hormonal disorders, and thus effects on fish growth, reproduction, and behavior (Gilliom 2007; Solomon et al. 2008; Xu et al. 2011; Srivastava et al. 2016; Soni and Verma 2018; Kumari 2020; Suchiang 2021). In addition, prolonged exposure to pesticides causes death, physical and morphological changes in fish (Yogesh et al. 2009). Therefore, in the present era, it is inevitable to use pesticides in agriculture, although their impact on non-target organisms is greater than their impact on the pests of interest (Suchiang 2021).
Chloroacetamides are among the most widely used herbicides for pre-emergence control of undesirable weeds and broadleaf weeds in corn, cotton, soybeans and many other crops (Jiang et al. 2016; Soni and Verma 2018). Among these, one of the most widely used herbicides is pretilachlor with the chemical formula of 2-chloro-2',6' -diethyl-N-(2 propoxyethyl) acetanilide (Partha et al. 2009; Jiang et al. 2016). The pretilachlor is exploited for rapid control during the unexpected growth of annual grasses and broadleaf weeds in rice fields (Jiang et al. 2016), which will naturally enter surface waters (Hladik et al. 2008).
The pollutants weakened the immune system of fish and increased the susceptibility of fish to pathogens (Abdel-Tawwab et al. 2010; Abdel-Latif et al. 2020; Yousefi et al. 2021b). Toxins and pesticides are the main causes of poisoning in fish. Of the thousands of chemicals released, pesticides cause high mortality, even at very low concentrations (Sanchez-fortun and Barahona 2005).
Plant essential oils, with their abundant antioxidant and antimicrobial properties, can exert positive effects on growth performance, resistance to environmental stress, infectious diseases, stimulation of nonspecific immune system and some blood parameters in livestock, poultry and aquaculture (Dugenci et al. 2003; Fallahi Kapoorchali et al. 2009; Awad and Awaad 2017; Abdel-Latif et al. 2020; Mohammadi et al. 2020; Abdel-Tawwab and El-Araby 2021; Ghafarifarsani et al. 2021a; Yousefi et al. 2021a; Yousefi et al. 2021b; Raissy et al. 2022). Improving the flavor of the diet by plant compounds stimulate growth, cause weight gain, stimulate the secretion of pancreatic enzymes, help digest and absorb important nutrients (Frankic et al. 2009; Abdel-Tawwab et al. 2010).
The important role of the immune system in maintaining the health of aquatic animals and ensuring their survival and proper growth during the breeding period, has led researchers to use a variety of chemical and natural compounds that stimulate and strengthen the immune system (Galina et al. 2009; Pandey et al. 2012; Reverter et al. 2014; Myszka et al. 2019; Alagawany et al. 2021). Numerous studies have shown that various plant extracts increase immunity, including increased serum complement levels, plasma protein content, serum globulin and lysozyme, as well as growth (Greathead 2003; Wu et al. 2007; Windisch et al. 2008; Alishahi et al. 2011; Harikrishnan et al. 2011; Abdel-Tawwab and El-Araby 2021; Ghafarifarsani et al. 2021a,b; Alagawany et al. 2021; Ghafarifarsani et al. 2022; Raissy et al. 2022). Therefore, food additives can affect the physiology of fish, including increasing immune responses and health status, improving growth rate, as well as protecting fish from harmful factors (Hajirezaee et al. 2019). Medicinal plants, including summer savory (Satureja hortensis), which contain substances that stimulate growth and appetite, as well as boost the immune system and many other beneficial properties, are used as a suitable alternative to chemical drugs (Akbarzadeh, 2003). The genus Satureja belongs to the family Lamiaceae (Hernández-Contreras and Hernández 2020), which is widely used in food preparation and has a special role in the pharmaceutical industry and traditional medicine (Taherian et al. 2019) and is rich in thymol and carvacrol (Hernández-Contreras and Hernández 2020). Other plants in this family include Thymus vulgaris, Origanum majorana and Origanum vulgare, which are known to have growth-promoting, antioxidant and immune-boosting effects in fish (Yousefi et al. 2021b).
Fish, like many other vertebrates, have defense mechanisms to counteract the harmful effects of reactive oxygen species (ROS) caused by the metabolism of various chemicals or xenobiotics. The first line of defense includes low molecular weight antioxidants (such as glutathione and vitamins C and E), and the secondary defense mechanism includes antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and glutathione S-transferase (GST) (Puangkaew et al. 2005; Blahová et al. 2013). Recent studies have shown that the toxicity of pesticides in fish may be associated with increased ROS production, which causes oxidative damage to biological systems (Yonar and Sakin 2011). The oxidative stress refers to an imbalance between the production and neutralization of ROS by antioxidant mechanisms within an organism (Puangkaew et al. 2005; Valavanidis et al. 2006); specification of antioxidant enzymes can help identify and highlight this stress.
Vertebrate immune systems, including the immune system of osteichthyes, react with certain sensitivities to xenobiotic exposure. In addition, many fish diseases are related to the quality of the environment and various environmental pollutants have immunotoxic potential (Betoulle et al. 2000). Because fish change their metabolic function to adapt to new conditions during stress, analysis of blood biochemical parameters can reveal the physiological state and health of fish (Agrahari et al. 2007; Silambarasan and Hemalatha 2015).
One of the most important components of the innate immune system in fish is the mucosal immune system. Fish epidermal mucus contains a variety of biologically active agents such as lysosomes, flavoenzymes, immunoglobulins and antimicrobial peptides. Mucous secretions by trapping high concentrations of toxins prevent their introduction into the fish body (Magnadottir 2006; Subramanian et al. 2007). Therefore, studying the parameters of the mucosal immune system will help us to understand the biological conditions of fish and reduce the immune function of fish due to stress caused by pollutants (Magnadottir 2006).
Common carp (Cyprinus carpio) is an economically important species in the world, accounting for 71.9% of freshwater production, and its production has increased from 2.9 million tons in 2008 to 4.1 million tons in 2017, with an increase of almost 30% (Mohammadi et al. 2020).
Despite significant progress, the aquaculture sector is always associated with challenges such as changes in water quality and pollution by pesticides, as well as nutritional problems. In addition, the importance of common carp and increasing the resistance and improving the immune system of this fish against environmental factors, as well as in order to increase growth and survival, it seems necessary to use some additives. Accordingly, the present study aimed to investigate the protective effect of summer savory (Satureja hortensis) essential oil (SEO) on growth and survival parameters, liver enzymes, immune serum, mucosal immune system and biochemical profiles of common carp (Cyprinus carpio) exposed to pretilachlor herbicide.