## 1 Introduction  
The pollution of water bodies with plant protection products is a huge problem worldwide. They often cannot be removed and can be absorbed by aquatic organisms. The pesticide level accumulated is often multiplied thousands of times higher than its concentration in the environment [1]. Pesticides can indirectly influence fish health through their feeding, even at low amounts [1]. Salmonids are very sensitive to xenobiotics, including pesticides, in their early life cycle [2]. Environmental pollutants are the reason for the early mortality of salmonids, well known as Syndrom M74 [3]; they reduce disease resistance and cause the long-term decrease in the humoral immune capacity [4, 5].  
The dithiocarbamate mancozeb (MZ) is a polymeric mixture of Zn- and Mn-ethylene dithiocarbamates. It was used in European Union (EU) countries as a fungicide [6]. The Commission Implementing Regulation (EU) 2020/2087 restricted the use of crop protection products based on MZ in the EU since 4 January 2022 [7]. However, worldwide, the amount used in the agriculture has increased significantly in recent years [8; 9]. Dithiocarbamates are strong chelating agents and can directly interact with signaling proteins and enzymes. In this way, they change the cellular metabolism [10]. [PERSON] and [PERSON] summarized the toxicity of various fungicides for different fish species: 7-day exposure in water containing 1.1 mg/L MZ caused adverse hematological changes in rainbow trout, e.g., hemoglobin and mean corpuscular hemoglobin levels were decreased [11].  
Rainbow trout ((_Oncorhynchus mykiss_ ([PERSON], 1792)) is a member of the Salmonella family, which are distributed in the word fish market. These fish products are safe, nutritious, and of high quality for the consumer [3]. Because of their high sensitivity to the environment, these fish species are used as an indicator of water pollution [12]. In an earlier study, our research team established that the concentration limit of MZ, permitted by the European legislation, does not affect the reproduction of rainbow trout. In particular, its toxic metabolite--ethylenethiourea (ETU)--does not accumulate in fish eggs and meat, it and does not make them harmful to consumers [8].  
Harmful environmental effects can be neutralized by using nutritional supplements that exhibit strong antioxidant capacities [3; 8; 13]. In the aquaculture industry, xanthophylls such as astaxanthin (Ax) and canthaxanthin (Cx) have been included in the diets of salmonids to provide a desirable coloration to these cultured organisms and to protect them from various diseases [14; 15; 16; 17]. Salmonids are able to absorb them from their diet [18]. A combination of both pigments in their diet gives a higher total xanthophyll accumulation than either one alone. Moreover, the rainbow trout \(O\). _mykiss_ and brook trout _Salvelinus fontinals_ ([PERSON], 1814) are able to absorb Ax and Cx in different muscle tissues from the nutritional base of the environment, which contains them in very low concentrations [19].  
The aim of the present study was to determine the accumulation of Ax and Cx in the liver and the gonads of rainbow trout (\(O\). _mykiss_) reared in water containing the fungicide MZ in a concentration level permitted by the European legislation (0.5 \(\mu\)g/L) and to evaluate its impact on their accumulation in different organs, with high significance placed on fish reproduction and safety. A diet poor in antioxidants or increased metabolic consumption in the females can lead to reproductive disorders [20].