| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 96 === Since fish is unable to synthesize carotenoids de novo, it has to rely on dietary supply. Dietary carotenoids concentration usually corresponds to body carotenoids content and concomitantly, the body color. Therefore, ornamental fish feed has to contain carotenoids to enhance and maintain fish body color, which is an important criteria reflecting market price of fish. Two experiments were conducted in this study to find out the effects of dietary astaxanthin and light regimes on survival, growth, pigmentation, and color fading of blood parrot (Cichlasoma var.). In Experiment I, 9 pigment diets supplemented with 3 astaxanthin sources (synthetic, red yeast Phaffia rhodozyma, and red algae Haematococcus pluvialis) at 3 carotenoid concentrations (50, 100, and 200 mg/kg) and a control diet without carotenoids supplement were fed to juvenile fish (average 1.2 g) for 48 weeks. Each diet had 3 replicate tanks. Only control diet was fed to all fish after 48th week for 6 weeks to compare astaxanthin sustaining ability of the original 10 diets. Survival, growth, and body surface astaxanthin content were measured at 12th, 34th, 48th, and 54th week. Until 12th week, body surface total astaxanthin (TA) of control fish was still no different from fish fed 6 pigmented diets. At 34th and 48th week, body surface TA of control fish was lower than fish fed all 9 pigmented diets. During pigment enhancing period, up to 48th week, body surface TA responded to various astaxanthin sources differently: synthetic ≧ red yeast ≧ red algae at 12th week, red algae ≧ red yeast ≧ synthetic at 34th week, and all three were of no difference at 48th week. This inconsistent response from these astaxanthin sources could be attributed to various types of astaxanthin, carotenoids composition, digestibility of source material, and absorb and conversion ability of theirs. Other possible affecting factors included fish size and astaxanthin deposition and saturation relationship. Dietary astaxanthin concentration had effects on body surface TA only at 34th week: 200mg/kg＞100mg/kg＞50mg/kg. This could be attributed to melanin still dominated at 12th week when fish was too small to be able to respond to dietary astaxanthin sensitively and astaxanthin accumulation had already reached saturation at 48th week. In Experiment II, 2 trials were conducted to find out the influence of illumination regime and dietary astaxanthin by their body size. In trial A, the same juvenile fish were reared under 4 treatments: 2 light regime (24 h light or dark) X 2 diets (supplemented with synthetic astaxanthin at 200 mg/kg and a control) for 48 weeks and 6 weeks for body astaxanthin deposition and withdrawal, respectively. In trial B, subadult fish (6.8 g) were reared under 6 treatments: 2 light regime (24 h light or dark) X 3 diets (2 supplemented with synthetic astaxanthin and red yeast at 200 mg/kg and a control) for 17 weeks and 9 weeks for body astaxanthin deposition and withdrawal, respectively. Both trials showed that survival and growth were not affected by treatments. For both trials, when fish all under the same treatment (synthetic astaxanthin 200 mg/kg) and at 12th week, subadult fish in trial B had body surface TA content 133.63 mg/kg, 6 times the TA content in juvenile fish in trial A, 21.83mg/kg. This indicated that big fish had higher astaxanthin deposition efficiency than small fish. In trial B, skin TA of fish in light group increased 89% in the first 17 weeks, but that in dark group increased 71%. During the 9 weeks’ pigment withdrawal period, skin TA of fish in light group decreased 41%, but that in dark group decreased only 18%. It appeared that both deposition and withdraw of astaxanthin in skin of blood parrot were faster under light than dark. These results can be applied to enhance and retain pigmentation by light regime manipulation.
|
|---|
