Aquaculture is the world’s emerging and growing food-producing sector that meets the demand for animal protein for the worldwide human population, which is expected to reach 9.7 billion by 2050. It plays an essential role in providing over half of all fish for human consumption and contributing to nutritional challenges, which is crucial for global food security and nourishment. Cyprinus carpio is one of the worldwide farmed fish species, due to its high consumer acceptance and tolerance of a range of environmental conditions, and has become a cornerstone in Asia, Central, and Eastern Europe. The increased production of this species is economically beneficial, mainly driven by the expansion of farming practices and intensive aquaculture systems characterized by high stocking densities, which produce chronic stressors on fish populations, elevating cortisol levels, which improve growth rates and suppress immune function. Many years ago, the aquaculture industry relied heavily on prophylactic use of chemotherapeutics and antibiotics to control diseases and improve efficiency. However, the consequences were severe, as antimicrobial-resistant. Furthermore, the determination of drugs in aquaculture carriages poses a risk to consumer safety, while the release of these compounds into the environment disrupts aquatic ecosystems. In response to these issues, stringent rules and bans on the use of antibiotic growth promoters in animal feed have been implemented in many countries, creating an urgent need for safe, effective, and biologically sustainable substitutes. Sustainable aquaculture has shifted to natural, plant-based additives, collectively known as phytogenics or phytobiotics. These substances demonstrated efficacy in enhancing growth performance and enhancing nutrient digestibility. Many phytogenics possess effective bioactive properties, such as antifungal, antioxidant, and anti inflammatory activities, including Allium sativum, Curcuma longa, and Xanthium strumarium L. These plants are regarded as natural immunostimulants and respond efficiently to pathogen challenges, thereby reducing disease prevalence of disease. Xanthium strumarium L., widely known as the cocklebur shrub of the family Asteraceae, is regarded as a harmful weed but is of importance in Asia, America, and Africa due to a long history of use in traditional medicine systems. Traditionally, it was used to treat illnesses such as arthritis, tuberculosis, headache, and rhinitis due to its diverse phytochemical constitution, presence of numerous bioactive compounds which are potent pharmacological activities, and its therapeutic potential. Aquaculture applications of X. strumarium extracts have widely documented antioxidant properties, hepatoprotective, and immunomodulatory. Furthermore, certain fractions of the plant control immune responses, regulate cytokine production, and stimulate lymphocyte proliferation. The increase in the concentration of phenolic and flavonoid compounds alleviates oxidative stress in rigorous farming conditions and reduces oxidative damage, keeping cellular health, and gives the plant with significant free-radical scavenging ability. X. strumarium, also known fundamental principle in phytogenic feed additives with the biological and beneficial effects, however, it is also recognized as a carboxyatractyloside compound that causes hepatic necrosis at high doses. Despite the significant research on its biochemical and pharmacological properties, the use of X

Taurine (Tau) is a neutral β amino acid present in animal tissues and animal by-products, whereas in plants it is scarce. In aquafeed industry, Tau is mainly used as a feed additive to promote growth of marine fish species with limited activity of cysteinesulfinate decarboxylase [1]. Tau supplementation is particularly important in feeds with high percentage of substitution of fishmeal (FM) with alternative protein sources, such as soy products that are often devoid or contain very low concentrations of Tau in comparison to FM. Aside from the promotion of growth, Tau has been found to have other functions. It is an anti-oxidizing agent that favors the protection of cells and tissues from toxic injury, stabilizes the cell membranes, reduces the membrane permeability, and scavenges the reactive oxygen species (ROS) [2;3]. ROS are by-products of normal physiological respiration in the mitochondria. However, disproportionate generation of ROS poses a serious problem to bodily homeostasis as it may cause oxidative stress generated by the imbalance between pro-oxidants and anti-oxidants [4]. Even a moderately intense physical activity, such as sustained swimming, that leads to an increased oxygen demand, can determine an increase of ROS level [2]. Sustained swimming in fish relies on the aerobic metabolism occurring primarily in the well-perfused red muscle in which the mitochondria (the main site of ROS formation) abundance is high [2;5]. Mortelette et al. [5] highlighted the link between aerobic swimming exercise at the expense of red muscle and ROS production in the eel. Accordingly, the present research aimed to study in European sea bass (Dicentrarchus labrax), the effects of dietary Tau on the swimming performance and the production of ROS during and increasing velocity swimming test, by assessing the critical swimming speed (U crit), the respiratory burst activity (RBA), and the metabolic oxygen consumption (MO 2).