**11. Carbohydrate metabolism**

Most researchers have reported that the increased blood glucose is usually observed in fish under undesirable conditions and it helps the animal by providing energy substrates to vital organs to cope with the increased energy demand (Banaee et al., 2008; Banaee et al., 2011). Elevation of blood glucose levels was widely used as a secondary marker of a stress response (Toal et al., 2004). On the basis of our literature review it is clear that insecticides can be acted as a stressor in fish. Because, hyperglycemia has been reported in many fish exposed to different insecticides. For example, increases in blood glucose levels have been reported in *Heteropneustes fossilis*(Saha and Kaviraj, 2009) and *Cyprinus carpio* (Banaee et al., 2008), *O.mykiss* (Banaee et al., 2011) after exposure to cypermethrin and diazinon, respectively.

Glycogenesis, glycogenolysis, glycolysis and gluconeogenesis are processes that play important roles in regulating blood glucose and carbohydrate metabolism. Glycogenesis is the process of glycogen synthesis from glucose molecules, in which various enzymes such as involved. Hexokinase (HK), glucokinase, and glycogen synthase are key enzyme in the glycogenesis process. Studies show that interfere with activity of these enzymes associated with insecticides exposure of organisms can inhibit glycogen stored in liver (Rezg et al., 2006). Reduced glycogen contents in live and muscle of fish have been reported by some authors.

Glycogenolysis is the catabolism of glycogen which leads to breakdown of glycogen to glucose and catalyzed by enzymes glycogen phosphorylase (GP), phosphoglucomutase (PGM), and glucose 6-phosphotase. Depletion of glycogen content in liver and muscle of fish during exposure to organophosphate insecticides was reported by many researchers (Ghosh, 1987; Nemcsok et al., 1987; Husain and Ansari, 1988).

In fish, catecholamine and corticosteroid hormones have an important role to promote gluconeogenesis. Cortisol is possible through increased levels activity of liver enzyme such as aspartate aminotransferase (AST), alanine aminotransferase (ALT) and tyrosine aminotrans‐ ferase (TAT) have a stimulatory effect on gluconeogenic mechanism.Since in the gluconeo‐ genesis process, glucose is produced from otherorganic molecules like pyruvate, lactate, glycerol, and aminoacids; elevated liver enzyme activity have an important role in the progress of the gluconeogenesis process. Although, pyruvate carboxylase, phosphoenolpyruvatecar‐ boxykinase (PEPCK), fructose 1,6bis-phosphatase, andglucose-6-phosphatase are key enzymes of this process, there are a limit information about their activities in the gluconeo‐ genesis process in fish exposed to insecticides.

Glycolysis is a cascade of biochemical reactions by which a molecule of glucose is oxidized to two molecules of pyruvic acid and two high energy electron carrying molecules of NADH. Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. Glycolysis is catalyzed by enzymes such as HK, phosphor-fructokinase (PFK), and lactate dehydrogenase (LDH).

LDH is an enzyme participated in anaerobic pathway of carbohydrate metabolism. The increase of LDH activity is a diagnostic index widely used to recognize increases of anae‐ robic metabolism resulting from depletion of energy under anaerobic and environmental stress conditions.The increase of LDH activity can be attributed to the conversion of accu‐ mulated pyruvate into lactate which is transported through muscle to hepatopancreas and regenerated glucose and glycogen to supply energy fish exposed to insecticides. In other words, the increase of LDH activity in liver and muscle reflects a possible improvement in tissue glycolytic capacity.
