In the experiment, fertilized eggs of grass carp Ctenopharyngodon idella Val. were exposed to copper (0.3 mg·dm-3) or lead (4.0 or 5.0 mg·dm-3) at 20, 24, 25, 28 or 30°C. Newly hatched larvae were counted and inspected. Body malformations of the larvae were examined. The proportion of deformed larvae was determined and the malformations were identified. The deformed larvae were described in detail and their images recorded with the MultiScan computer image analysis system. The highest hatching success rate was observed in the control fish kept at 24-25°C. Although malformations were observed among them, they were rare. The most common malformations were single vertebral abnormalities. Incubation at the temperatures below and above the optimum range resulted in a reduced hatching success rate and an increased frequency of body malformations (even to 100%). Exposure to the heavy metals, too, considerably reduced the hatching success rate and increased the frequency of body malformations. These included various vertebral curvatures, yolk sac deformations, and shortening of the body. The malformations observed in the grass carp larvae were very similar to those reported earlier from the common carp.

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