Haemato-biochemical studies in rainbow trout infected with Saprolegnia were carried out under temperate climatic conditions of Kashmir valley to find out the variation in blood parameters. The trial was carried out on 405 cultured rainbow trout fish ranging in length from 47.8 to 69.8 cm and in weight from 1300 to 1920 g. The same experiment was carried out on 2,70000.00 trout fish eggs from November 2010 to April 2011 at a trout fish farm, in Kokernag, India, on account of the susceptibility of eggs to fungal infestation. The infected fish showed signs of lethargy, irritation, loss of appetite, haemorrhages at the base of fins and deep wounds at the sites of severe infection associated with cottony wool like tufts on both the dorsal and ventral sides of the body. The fungi were isolated at high percentages from skin followed by fins and mouth. The haemato-biochemical profile was studied in forty (40) normal and forty (40) infected fish. The haemoglobin content, total erythrocyte count, packed cell volume, lymphocyte  percentage, total serum protein, albumin and globulin levels decreased significantly (p<0.05) in the Saprolegnia infected fish as compared to that in the control. The white blood cells, erythrocyte sedimentation rate, mean corpuscular haemoglobin, mean cell volume, heterophill percentage and total serum glucose showed significant increase in the infected fish irrespective of sex. The infection was more pronounced during the winter season (Temp.<10°C

) as compared to that in summer (temp.<17°C). Fungi induced stress leads to haemostatic imbalances in fish reflected in the haemato-biochemical profile and can thus be used as an indicator for Saprolegnia induced infection.