| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 94 === Abstract
Mozambique tilapia Oreochromis mossambicus held in 27 ºC were then cultured onward at 19, 23, 27 (control), 31 and 35 ºC, and were examined for non-specific cellular and humoral responses at 12-96 h. Total leucocyte count decreased significantly when fish were transferred to 19 and 23 ºC after 48 and 96 h, and when transferred to 35 ºC over 12-96 h, respectively. Concerning the non-specific cellular response, respiratory burst decreased significantly when fish were transferred to 19, 31 and 35 ºC over 24-96 h, whereas phgaocytic activity and phagocytic index decreased significantly when fish were transferred to low temperatures (19 and 23 ºC) and high temperatures (31 and 35 ºC) over 12-96 h. Concerning the non-specific humoral response, lysozyme activity decreased significantly when fish were transferred to 19 ºC after 12, 24, 48 and 96 h, but increased significantly when fish were transferred to 31 and 35 ºC over 48-96 h. Alternative complement pathway (ACH50) decreased significantly when fish were transferred to 19 and 23 C after 12 h, but increased when transferred to 31 and 35 ºC after 24 h. The multivariate discriminant analysis revealed that decreases in phagocytic index and respiratory burst were responsible for separating the two temperature groups (19 and 35 oC) from the control group (27 oC) indicating that tilapia when transferred from 27 oC to 19 and 35 oC reduce their immunity.
In another experiment, tilapia held at 27 ºC were injected with Streptococcus iniae grown in tryptic soy broth (TSB) at a dose of 1x107 colony-forming units (CFU) fish-1, and then reared onward at water temperatures of 19, 23, 27 (control), 31 and 35 ºC. Over 48-168 h, the cumulative mortality of S. iniae injected–fish held in 19 and 35 ºC was significantly higher than that of injected-fish held in 23, 27 and 31 ºC.
It was concluded that transfer of tilapia O. mossambicus from 27 ºC to low temperatures (19 and 23 ºC) after 12 h, and when transferred to high temperatures (31 and 35 ºC) reduced their immunity. Moreover, tilapia under temperature stress at 19 and 35 ºC from 27 ºC decreased its resistance against S. iniae infection.
Keywords: Mozambique tilapia; Oreochromis mossambicus; Temperature; Challenge Non-specific cellular response; Non-specific humoral response, Streptococcus iniae, Multivariate analysis
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