PREFERRED TEMPERATURE OF GRASS CARP, CTENOPHARYNGODON-IDELLA (VALENCIENNES), AND BREMA CARP, MEGALOBRAMA-AMBLYCEPHALA (YIH), (PISCES, CYPRINIDAE) IN HORIZONTAL AND VERTICAL GRADIENTS

The preferred temperatures of grass carp, Ctenopharyngodon idella (Val enciennes), and brema carp, Megalobrama amblycephala (Yih), were deter mined individually and together in both horizontal and vertical gradie nts. No significant difference was found by two methods between the pr eferred temperatures in either species of carp (28.0-28.5 degrees C) w hen the fish were placed individually. However, when the two species o f carp were placed together, C. idella was displaced thermally, prefer ring a temperature of 23.5 degrees C, which was significantly lower th an that obtained when it was held separately. This suggests that, if b oth species of carp are placed in ponds forming part of a Chinese poly culture system, C. idella will seek out a lower temperature as a mecha nism to avoid competition, and therefore, the growth of this species w ill be reduced.