Fish meat has a high content of high-quality protein, and fish oil is rich in omega-3 fatty acids, so it is well-known that fish consumption has beneficial effects on human health (Abbott et al., 2007). World fishery production reached its highest level in 2018, reaching 96.4 million tons, an increase of 5.4% compared to the previous three years, and per capita fish consumption continued to increase (FAO, 2020). Various fish species have been produced in oceans, marine, and inland waters for years. However, fish are exposed to a significantly higher number of pathogens than non-aquatic vertebrates, and each millimeter of seawater contains millions of bacteria and viruses, both pathogenic and non-pathogenic species (Fuhrman, 1999). In addition, fish encounter many microorganisms from many species in saltwater or inland farming (Jeffries et al., 2014).
Therefore, in natural and industrial fish production, fish can be exposed to significant numbers of microorganisms at every production stage after the hatchery period. In production areas, fish experience stress due to excessive stocking density, handling, production processes and new water environment, and in all stress situations, fish body resistance decreases, and disease incidence and losses may increase (Vargas-Chacoff et al., 2016). Using natural additives such as plant essential oils in feeds can improve feed utilization rates, body weight and marketing weight (Velasco & Williams, 2011), disease resistance, and animal health (Tanabe & Yoshida, 2003).
Oregano is a well-known medicinal plant of the mint family (Lamiaceae) (Meyers, 2005) and contains essential oil, the main components of which are thymol and carvacrol, and these active substances have antioxidant (Couladis et al., 2003; Tepe et al., 2004), antibacterial (Ugur & Duru, 2009; Vági et al., 2005), antifungal (Bouchra & Achouri, 2003), cytotoxicity activity (Sivropoulou et al., 1996; Wilson et al., 2007). Cinnamon is a plant from the Lauraceae family and contains polyphenols, tannins, sapones, flavonoids (Kwon et al., 2009) and has anti-inflammatory(Singh, 2007), antioxidants (Matan et al., 2006; Rozi, 2016) and antimicrobial (Kwon et al., 2009; Qin et al., 2003) anti-inflammatory (Gruenwald & Freder, 2010), and antimicrobial (Lee et al., 2005) activities.
The application of cinnamon and its products as a natural dietary supplement has become beneficial for fish as it promotes fish growth, feed utilization or resistance to pathogenic bacteria (Turan, 2007). On the other hand, after the ban on antibiotics as growth promoters in diets, natural ingredients have been used as alternatives in animal production and the prevention of cross-immunization of some antibiotics in humans through the consumption of animal products, their costs and safety have been taken into consideration (Manyi-Loh et al., 2018). Plant essential oils contain highly volatile compounds consisting of aldehydes, ketones, hydrocarbons, alcohols, ethers, phenols and esters of phenolic and terpenic origin (Thompson et al., 1989). However, sufficient experiments have not been conducted regarding plant essential oil types to determine their effectiveness in fish diets. Therefore, this study evaluated the effect of adding thyme and cinnamon essential oil to the trout diet on performance, carcass, meat characteristics and blood parameters.
Various fish have been produced in the ocean, sea, and inland waters for many years. However, fish are exposed to a significantly higher number of pathogens than non-aquatic vertebrae, and every millimeter of seawater contains millions of bacteria and viruses, both pathogens and non-pathogens (Fuhrman, 1999). In addition, fish encounter many microorganisms from many species in saline or inland farming (Jeffries et al., 2014). Therefore, in both natural and industrial production, fish can be exposed to many microorganism damage at every production stage after incubation. In production areas, fish experience stress due to excessive stocking density, handling, production processes, and the new aquatic environment, and in all stress situations, fish body resistance decreases, and disease incidence and losses may increase (Vargas-Chacoff et al., 2016).