Abstract
Increase of water temperature as a consequence of global warming is anticipated to affect the
physiological activities Of fish, especially in tropical regions. Four experiments were conducted to
understand the effect of high temperature on embryogenesis and physiological activities, the
commercially imprtant rohu carp (Labeo rohita) was selected for the present study. In the first
experiment, rohu embryos and larvae were reared at four different temperatures (30, 32, 34 and 360C),
and indices of their hatching, development. and mortality were observed throughout early
development. Embryos exposed to 30 and 320C showed normal development with highest rates of
hatching success. Embryos at 340C displayed evidence of damaged zygotes, cellular deformities,
damaged yolk sac coupled with shortest incubation time and the lowest rates of hatching success. No
hatching was observed at 360C. and the embryos at this temperature displayed coagulated organs,
dark yolk sac, irregular segmentation and pustules. Larvae of rohu exposed to 34 and 360C showed
developmental deformities (fusion in the eye, axial curvature, yolk sac ulceration, blood coagulation,
tail shortening and ulceration) and minimal survival. In the second experiment, the effects Of three
acclimated temperatures (30, 33 and 360C) on high temperature tolerance (CTmax) of rohu were
evaluated. To determine the CTmax, the mujor hemato.biochemical indices - hemoglobin (Hb), red
blocxi cell (RBC), white blood cell (WBC), glucose levels, and erythrocytic nuclear
abnormalities (ENAs) and erythrocytic cellular abnormalities (ECAs) of peripheral erythrocytes were
analyzed in the fish sampled at the start and end point from each acclimated temperature group.
Significantly decreased CTmax Of the fish was found at 360C compared to 300C and 330C. The fish in
the highe;t (360C) temperature were found with significantly lower Hb and RBC content and
significantly higher WBC and blocxl glucose levels than that of the fishes in the lowest (300C)
temperature both at the start and end points of rearing. The highest frequencies of ENAs and ECAs
were found in the highest (366C) temperature group compared to the lowest (300C) temperature group
at both the points. In the experiment trial, growth performance of rohu fingerlings were evaluated
after rearing in the three temperature conditions for 60 days. The growth parameters - final weight
gain, weight gain and specific growth rate were the highest at 330C and the lowest at 360C.
Lowest FCR value was found at 33 oc. Finally, the effects of high temperature on hemato-biochemical
parameters and erythrocytes cellular and nuclear structures in rohu were studied. Exposure to high
temperature decreased Hb and RBCs and increased the WBC and blood glucose levels of the fish.
Frequencies of ECA and ENA were found to be increased at high temperature. High temperature
significantly increased the number of neutrophils whilst decreased the number of lymphocytes.
Overall, this study confirmed that exposure to high temperature (360C) is stressful to Indian major
carp rohu.