**9. Immune system**

The immune system of fish is important for defense against a variety of pathogens. The system is very sensitive to homeostatic adjustments via endocrine regulation and is influenced by the biochemical status of the nervous system. Thus, any impairment in the nervous system and disturbance in the biochemical homeostasis can weaken the immune system of fish.

Different insecticides at sub-lethal levels have been recognized as stressors causing im‐ mune-suppression in fish (Werner and Oram, 2008). In addition, some insecticides may exert immunotoxic effects by altering the transcription of important mediators of the fish immune system (Eder et al., 2009). Effects of insecticides like P,P'-DDE, lindane, cy‐ permethrin, chlorpyrifos, diazinon on the immune factors of fish such as Interleukin-1β (IL-1β), IL-1β receptor (IL-1R1), Interferon gamma (IFN-γ2b), TNFα, MHCIα, MHCIIα, Mx, TLR9, IγML and C- reactive protein (CRP), TCRα in head- kidney leucocytes, Lyso‐ zyme activity, chemiluminuscence (CL) response and immunocompetent cells popula‐ tion size, IgM levels, value of white blood cells (WBC) and respiratory burst activity, head kidney phagocytes and peripheral blood leucocytes, etc., have been reported by scholars (Betoulle et al., 2000; Khoshbavar-Rostami et al., 2006; Banaee et al., 2008; Cues‐ ta et al., 2008; Girón-Pérez et al., 2009; Shelley et al., 2009; Ahmadi et al., 2011; Jin et al., 2011, Wang et al., 2011). The exposure to sub-lethal concentrations of insecticides is what probably makes fish vulnerable to infectious diseases because of their immune-de‐ pressiveeffects (Zelikoff et al., 2000). For example, the susceptibility of juvenile chinoock salmon (*O.tshawytscha*) to infectious hematopoietic necrosis virus was significantly in‐ creased in fish exposed to sub-lethal concentrations of esfenvalerate (Clifford et al., 2005). Similar results were reported in goldfish and common carp that were exposed to carbaryl and lindane respectively (Shea, 1983; Shea & Berry, 1984; Cossarini-dunier&Hat‐ tenberger, 1988).

14th and 28th day. However, elevated levels of this enzyme in plasma indicate a transient damage to either muscle fibers or other tissues. Previous results reported that continuous exposure to acute pesticide (bifenthrin) concentrations resulted in significantly increased levels

Creatinine is a breakdown product of CK in muscle. The creatinine test has been usually used to diagnose impaired kidney function and to detect renal damage (Toffaletti and McDonnell, 2008; Banaee et al., 2011) However, the lack of changes in creatinine levels are in accordance with the previous results obtained by Gilbert et al (1989) and Banaee et al. (2011) which reported that plasma creatinine was usually not an accurate biomarker to distinguish dysfunction in kidney tissue. The creatinine test has been usually used to diagnose impaired

The alkaline phosphatase (ALP) plays a significant role in phosphate hydrolysis and in membrane transport as well as is a good bio-indicator of stress in biological systems. The importance of measuring alkaline phosphatase is to check the liver dysfunction (Banaee et al., 2011) and the cellular membrane health. Alkaline phosphatase (ALP) is an enzyme found in different body tissues; in liver, is produced by the cells lining the small bile ducts (Agrahari et al., 2007). Increased activity of ALP in blood plasma on 14th day may be related to hepatic tissue damage and dysfunction due to pesticide toxicity; the elevation in ALP activity on may be due to an increase in transphosphorylation activity (Sharma, 1990). Agrahari et al. (2007) found increased levels of ALP in plasma of *Channa punctatus* exposed to monocrotophos. These changes in ALP activities in plasma were earlier reported in tilapia (Rao, 2006) and in common carp (Banaee et al., 2008). The return of ALP activity to basal values could indicate a fish

Acid phosphatase plays an important role in carbohydrate metabolism. This enzyme can be found inside the membrane of lysosomes. So, any damage to the membrane of lysosomes can

The immune system of fish is important for defense against a variety of pathogens. The system is very sensitive to homeostatic adjustments via endocrine regulation and is influenced by the biochemical status of the nervous system. Thus, any impairment in the nervous system and

Different insecticides at sub-lethal levels have been recognized as stressors causing im‐ mune-suppression in fish (Werner and Oram, 2008). In addition, some insecticides may exert immunotoxic effects by altering the transcription of important mediators of the fish immune system (Eder et al., 2009). Effects of insecticides like P,P'-DDE, lindane, cy‐ permethrin, chlorpyrifos, diazinon on the immune factors of fish such as Interleukin-1β (IL-1β), IL-1β receptor (IL-1R1), Interferon gamma (IFN-γ2b), TNFα, MHCIα, MHCIIα, Mx, TLR9, IγML and C- reactive protein (CRP), TCRα in head- kidney leucocytes, Lyso‐

disturbance in the biochemical homeostasis can weaken the immune system of fish.

kidney function and to detect renal damage (Toffaletti and McDonnell, 2008).

adaptation to the diazinon treatment at sub-lethal concentrations.

cause the release of this enzyme into muscle and increase its levels.

**9. Immune system**

of CK in common carp at 96 h (Velisek et al., 2008).

114 Insecticides - Development of Safer and More Effective Technologies

Lysozymes are a family of enzymes with antibacterial activity characterized by the ability to damage the cell wall of bacteria. Ahmadi et al. (2011) found that exposure to diazinon induced a dose-dependent decrease in rainbow trout plasma lysozyme activity. Peroxidases are a large family of enzymes which play important role as natural antibacterial agent in animal immune system, e.g., myeloperoxidase (Clark and Klebanoff 1975). Ahmadi et al. (2011) indicated that diazinon treatment of rainbow trout significantly affected the peroxidase activity.

Globulin is made up of subunit of α1, α2, β, and γ globulins, which are considered as the source of almost all the immunologically active proteins in the blood (Jha et al., 2007; Ahmadi et al., 2012).Decreased globulin levels have been reported in immune deficiency. In fact, the effect of diazinon on the immune system of tilapia (*Oreochromis niloticus*) and beluga sturgeon (*Huso huso*) as immunomodulator has been studied by other authors (Khoshbavar-Rostami et al., 2006). Significant decrease in globulins levels in plasma of fish exposed to diazinon could be due to a disruption in protein biosynthesis (Ahmadi et al., 2011). In the other word, diazinoninduced tissue destruction and hepatocyte apoptosis might be the most important agent responsible of reducing the synthesis of total protein, albumin, and immunoglobulin by the liver (Banaee et al., 2011)

Complement includes over 20 different plasma proteins that are produced by a variety of cells including, hepatocytes, macrophages, and gut epithelial cells. Some complement proteins bind to immunoglobulins or to membrane components of cells. The complement system is an essential and effective part of the innate immune system. It can rapidly distinguish and opsonize bacteria for phagocytosis by specialized phagocytes or destroy them directly by membrane disorder (Rooijakkers and van Strijp 2007; Ahmadi et al., 2012). Ahmadi et al. (2011) believed that significant depression of complement levels clearly indicated the comprehensive effects of diazinon on immune system of rainbow trout. Thus, insecticides may alter the function of the immune system and result in immune-depression, uncontrolled cell proliferation, and alterations of the host defense mechanisms including innate immunity and acquire immunity against pathogens.
