Abstract: To investigate effect of low temperature Stress on cell morphology of liver, spleen and gill in Egyptian strains of Nile tilapia, 135 tilapias were selected to study the effects of different cold stress on blood physiological and biochemical changes using artificial indoor cooling and electron microscopy. The average body weight of the tilapia were (150±2) g which were randomly divided into 25 ℃, 15 ℃ and 12 ℃ 3 groups with three repeats, 15 tilapias for each repeat. The results showed that tilapia went into at 15 ℃ 16 d, at 12 ℃ of 72 h tilapia were in a coma and death. The damage degree of liver, spleen and gill cells of tilapia were enhanced with water temperature reduced, at 12 ℃, the most serious occurred. when the temperature was 15 ℃, the edge of the liver cells was not clear and formed the small crushed, the edge of the spleen appeared minor dissolved, part of the gill lamellae was fractured and capillary mild hyperemia; when temperature was 12 ℃, the number of mitochondria in liver cells decreased with serious structural fragmentation. Endoplasmic reticulum structure was at a state of fragmentation and the edge of the spleen tissue began to dissolve. Similar changes appeared in spleen cells and liver cells gill lamellae faratured and capillary congested seriously.

Key words: low temperature stress, Egyptian strain of Nile tilapia, liver, spleen, gill, cell morphology