Grass carp acclimated to 3, 5, 7, and 99'00 salinities were tested for salinity tolerance. The upper tolerance limit (LS,,) for 3 and 5%0, and 7Yooacclimated fish were 1 4 2 and 14.00/00, respectively. Fish acclimated to 9%0 had a 50% mortality at an estimated salinity of 16.0%, for 24 h exposure. Weight losses for the 3 and WOO acclimated fish were significantly lower than for those acclimated to 9%0.

Food intake and growth of hybrid carp (female grass carp,Ctenopharyngodon idella x male bighead, Aristichthys (Hypophthalmichthys) nobilis) fed on zooplankton and CharaHybrid carp were raised in 165 1 indoor tanks. Two tanks were used in this study each stocked with five fish (average total length and weight=235.7 mm; 116.1 g); one tank was provided with zooplankton and the other with zooplankton and Cham sp. The hybrids fed actively on zooplankton at an average daily rate of 39% and Chum at 2.6% by body weight. Growth was estimated as 0.36% (0.43 g) per day. The hybrids on the two food types showed no significant differences either in plankton consumption or growth rate.

Hybrid carp and grass carp from the zygote to the prolarval stage and adults were compared to establish distinguishing characteristics. Zygote diameter, yolk sac and embryo length were not different between the fishes. Body pigmentation patterns showed distinct separation among the prolarvae of the hybrids and grass carp. Total and preanal myomeres were higher in grass carp larvae than in the hybrids. The grass carp and hybrid larvae also differed in 38% ofthe proportional morphometric characters.Average meristic counts of adults were significantly higher in hybrids compared with grass carp. Adults of the two fishes showed significant differences in 63% of the proportional morphometric measurements. Gill raker counts showed no overlap and lateral line scales were smaller and more numerous in the hybrid adults.