The distribution of apple snail Pomacea canaliculata is islandwide but Pomacea scalaris is only found in southern Taiwan. In order to gain more information on the not well-known invasive species of P. scalaris, the growth and feeding of P. canaliculata and P. scalaris were studied. The hatching period of P. canaliculata (10.4¡Ó1.3 days) was shorter than that of P. scalaris (12.2¡Ó2.3 days). And, the hatching size of P. canaliculata was also smaller. Two weeks after hatching, a significant higher growth rate in P. canaliculata had been found. The 75-day growth equations for P. canaliculata and P. scalaris were y = 0.29x + 1.09 (p < 0.001) and y = 0.16x + 1.68 (p < 0.001), respectively. Feeding structures of mandible, radulae, central tooth and stomach in P. canaliculata were larger than that of P. scalaris. But, there was no significant difference in the length of gut between the two species. Food passing time in P. canaliculata (1.4¡Ó0.7 days) was less than that of P. scalaris (2.9¡Ó0.7 days). And, the approximate digestibility per day of P. canaliculata (44.41¡Ó24.02%) was higher than that of P. scalaris. Through the analyses of £_13C, £_15N, stomach content and feces, it is known that they have the same trophic level with similar food sources. Additionally, the values of £_13C and £_15N were significantly different between sites of JiouRu and Wugou-shui, Pingtung. In other words, the feeding environments were different between the two sites. Based on the results, it is concluded that the superiority of growth and feeding performance in P. canaliculata is important in shaping its wide distribution in Taiwan.

The distribution of apple snail Pomacea canaliculata are island-wide but Pomacea scalaris is only found in southern Taiwan. In order to gain more information on the not well-known alien invasive species, comparative studies on the reproduction and thermal tolerance of P. canaliculata and P. scalaris were conducted. Sexual dimorphism in shell morphology has been found in both species, with wider operculum in males. Positive correlation between shell length and penis sheath length or penis length has been observed in male P. canaliculata and P. scalaris, based on the samples collected during the period of December 2004 and March 2006, The width of penis sheath in P. canaliculata was greater than in P. scalaris. Positive correlation between shell length and the height and width of vestigial penis in female P. canaliculata and P. scalaris was also found. The width of vestigial penis in P. scalaris was greater than in P. canaliculata. Gonadosomatic index (GSI) in male P. canaliculata and P. scalaris was 68 and 60% and 31 and 33% in females. Their reproductive cycle was annual without seasonal peaks. Significant difference in thermopreferrenda was found between P. canaliculata and P. scalaris. The 24, 48 and 72-h lethal thermal minima temperatures in P. canaliculata and P. scalaris were similar, i.e. 9.8¡V11.8¢J. And, the 24, 48 and 72-h lethal thermal maxima temperatures were 33.1¡V35.9¢J. Based on the results, it is known that P. canaliculata and P. scalaris reproduce year-round and temperature is not a major factor in shaping the species distribution pattern in Taiwan.