(sorumlu yazar) Celal YILMAZ Mahmut Ali Oksidatif oksidatif stres Anahtar kelimeler ri
ABSTRACT
The reactive oxygen species formed as a result of oxidative reactions bind to cellular structures such as proteins, lipids, carbohydrates and DNA, causing structural damage. Therefore, this oxidative damage caused by reactive oxygen derivatives is called oxidative stress.
Environmental conditions known to cause oxidative stress in aquatic organisms are generally; temperature, oxygen level, salinity, seasonal rhythm changes, transition metal ions, pesticides and petroleum derivatives. The formation of free radicals in fish starts and increases due to heavy metals, pesticides and environmental pollution.
In addition, important sources of oxidative stress encountered in addition to known environmental factors in growing conditions are hunger and disease states. The situation in fisheries caused by the diseases of fish is a source of stress in itself. In this case, the diagnosis and treatment process should be initiated. Fish exposed to hunger conditions; gives many physiological symptoms. Hormonal and enzyme changes are the leading ones. Especially because hunger factor is directly related to energy metabolism, it causes some negative changes in the liver where energy activities are intense. It is important to remember that it is important in feeds used in aquaculture. Not only in fasting conditions, but also in fish fed with poorly adjusted feeds, stress effects are seen. Oxidative stress is usually seen in fish fed with dense fatty feeds due to lipid octidation. In addition, diets prepared differently from the feeding habits of fish can create these negative situations. For example, carnivore nutritional properties of fish containing intense carbohydrate feed, such as use. Along with feeding and disease factors, environmental factors should be considered in aquaculture establishments. The water temperature, salinity, pH, oxygen and the levels of the macro and micro elements should be determined well. Therefore, oxidative stress is one of the most important issues to be considered in aquaculture in recent years.
In this review, it is aimed to give detailed information about the effects of oxygen on vital functions in fishes, reactive oxygen species formed as a result of oxidative reactions and especially the most important oxidative stress factors encountered in fish farming.
Key words: Aquaculture, Fish farms, Oxidative stress
1. INTRODUCTION
Oxygen, while providing beneficial benefits for all these vital functions, can also turn into very dangerous toxic structure, i.e. free radicals. (Buyukguzel, 2013).
The reactive oxygen species formed as a result of oxidative reactions bind to cellular structures such as proteins, lipids, carbohydrates and DNA, causing structural damage. Therefore, this oxidative damage caused by reactive oxygen derivatives is called oxidative stress (Rodriguez-Ariza,
Alhama, Diaz- -Barea, 1999).
Oxidative stress defines the deterioration of prooxidant-antioxidant balance in body and tissues in favor of prooxidants. More specifically; Oxidant + prooxidant = antioxidant.
Free radicals are atoms or molecules with unpaired electrons, many of which are highly reactive. The electron fields of these radicals from other molecules are referred to as OXIDAN and
causing ROS production or by inhibiting antioxidant systems are called PRO-OXIDAN.
Antioxidant is a defense system that works in the body to prevent the formation of ROS and to prevent damage caused by these substances. Antioxidants are substances that react rapidly with radicals and prevent the progression of peroxidation. The roles of antioxidants include neutralizing excess free radicals, protecting cells against the toxic effects of free radicals, and contributing to the prevention of diseases.
Environmental conditions known to cause oxidative stress in aquatic organisms are generally; temperature, oxygen level, salinity, seasonal rhythm changes, transition metal ions, pesticides and oil
free radicals in fish begins with heavy met 2006).
The reactive oxygen species (ROS) produced and the resulting free radicals (FR) are results of normal cell metabolism, and many of these compounds play a key role in various metabolic pathways. Many of these components are essential in the organism defense and their byproducts are considered potent bactericides that act actively in the destruction ofinvasive pathogens (Cross et al. 1987, Dong et al. 2017, Biller-Takahashi et al. 2015).
2.OXIDATIVE STRESS IN AQUATIC ORGANISMS
Generally, oxidative stress is affected by different factors in aquatic organisms. These can be classified as external and internal factors.
External factors are related to the environment in which the fish live. Therefore, temperature, oxygen and salinity are the external factors that cause oxidative stress of the fish.
Internal factors are generally related to the situation of the fish itself. Internal factors; reproduction, feed and deprivation, physical activity, the age of the fish.
2.1.EXTERNAL FACTORS 2.1.1.Temperature
In all living things, temperature increase increases metabolic activity. Hence increased metabolism increase the need for oxygen. The oxidan level increases. As a result; High temperature = High ROS.
According to known thermodynamics principles, an increase in temperature is associated with an increased metabolic rate (Q10 Effect), leading to an increase in oxygen consumption, an increased flux at the level of the electron transportchain and a greater production in ROS (Halliwell & Gutteridge, 2015). Consequently, one would expect a higher production of ROS when water temperatures are higher.
2.1.2.Oxygen
Oxygen is essential for metabolic activities and life in aquatic organisms. Low oxygen causes a low metabolic rate. This means a small amount of ROS production.
In fact, when a general assessment is made, ROS production is associated with the amount of oxygen in an organism (Jamieson et al., 1986). Increase in oxygen levels increases the chances of electrons to escape and complexes in the electron transport chain and consequently creates ROS. Fish have developed ways to avoid rich oxygen environments. Due to their nature, they reduce their effectiveness in order to get out of this environment (Lushchak, 2011).
2.1.3.Salinity
Differences are observed in freshwater and saltwater fish. The adaptation of anadrom (growing in fresh water and growing in salt water) and catadrom (growing in salt water and growing in fresh water) is high. Salinity changes increase the ROS level. Therefore, it causes increased oxidative stress.
Marine fish species experience some environmental changes compared to freshwater fish due to highly variable environments.
There are many fish species, life stories that involve major salinity changes. For example, when migrating from freshwater rivers, they migrate to sea water (eg salmonids) or from waters such as globally high salinity low and vice versa (eg tuna, billfish).
Salinity changes elicit physiological and behavioral responses such as the need for osmoregulators. There is evidence that stress associated with changes in salinity causes an increase in ROS production (Liu, et al., 2007).
2.2.INTERNAL FACTORS 2.2.1.Reproduction
It is a highly demanding activity that increases the metabolic rate over a long period of time and thus increases the production of ROS. Alternatively, fish try to reduce oxidative damage by consuming more antioxidants to produce higher quality eggs (Alonso-Alvarez et al., 2004).
2.2.2.Feed and deprivation
The term dietary oxidative stress is used to describe the imbalance between proxidants and antioxidants from an insufficient nutrient source (Sies, Stahl, & Sevanian, 2005).
The quality of the feed contains the necessary antioxidants. Vit A, E, C and B9, selenium balance should be observed in feed. If plant-based feeds are to be used, some supplements may be made to these feeds.
2.2.3.Physical activity
The relationship between physical activity and oxidative stress is generally expressed as follows. As a result of increased mitochondrial activities, metabolic rate increases. Therefore, intensive oxygen use and consequent the amount of ROS is increasing. There are few studies on the subject. In fish, variable results were observed in response to different degrees of physical activity.
The age and antioxidant capacity of the fish are inversely proportional. Wdzieczak et al., (1982), in many fish species; rufous (Rutilus rutilus) burbot (Lota lota), abramis (Abramis brama), freshwater perch (Perca fluviatilis), silver carp (Hypophthalmichthys molitrix), perch (Dicentrarchus labrax), scorpion fish (Scorpaena porcus) antioxidant capacity.
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