<i>Tilapia</i>属の水温に対する反応の種間差異

Abstract

1. Influence of different acclimation temperature was observed with the cruising performance in flowing water in a V-shaped conduit one m long under the test temperature 10 to 40°C with two species, Tilapia mossambica and T. sparmanni acclimated at 20° and 30°C and kept at 24°C (Av. temperature) before test (Fig. 4), and the influence was found more significant in the former species. 2. The comparison of cruising performance among seven species of Tilapia acclimated at 25°C for 20 days was carried out by a same apparatus under the test temperatures of 10° to 40°C at intervals of 3°C, and these seven species showed their maximum of performance at four test temperatures (Fig. 5), which may be presumed to categorized eventually into two groups; 28°-32°C: T. galilaea, T. mossambica, T. nilotica, T. macrochir and T. zillii, and 24°-28°C: T. macrocephala, T. sparmanni. 3. The preliminary test for temperature tolerance was made finding a correlation between body length and chill tolerance (Fig. 5). Secondly, T. mossambica about eight cm long in S. L. kept at 24°C (Av. temperature) revealed “apparent death” in 2.5 minutes at 1°C, and more than ten minutes following lead the fish to true death. Thus, “apparent death” was defined and adopted. 4. The influences of acclimation to temperature tolerance were tested at 1°, 5°, 10°, 35°, 40°C, with two species of Tilapia as in crusing performance, and significant influence was observed (Fig. 6), and the influence was more regular in T. mossambica than T. sparmanni, a similar result observed in cruising performance experiment. 5. The difference of tolerance among three species of Tilapia was tested with fishes acclimated at 25°C for 20 days, an order of tolerance was, T. sparmanni>T. mossambica>T. nilotica at low test temperatures (1°, 5°, 10°C), but the order became opposite direction at high temperatures (35°, 40°, 45°C) (Fig. 7).