为研究饲料中不同蛋白源对军曹鱼幼鱼碳、氮稳定同位素分馏的影响, 配制3种等氮等能饲料。D1以鱼粉为蛋白源, D2和D3饲料中分别以啤酒酵母和玉米蛋白替代10%的鱼粉蛋白, 投喂幼鱼24d。结果表明, 啤酒酵母和玉米蛋白替代10%的鱼粉蛋白后, 幼鱼的体质量增加率显著下降。随养殖时间的延长, 所有处理组幼鱼的碳稳定同位素比率δ13C逐渐上升而氮稳定同位素比率δ15N逐渐下降; 虽然全鱼和肌肉δ15N的变化速度存在差异, 但各饲料组全鱼和肌肉的δ13C和δ15N都在24d后与饲料达到平衡。当饲料中10%的鱼粉蛋白被啤酒酵母和玉米蛋白替代之后, 幼鱼肌肉和全鱼样品与饲料相比的碳同位素富集Δ13C值下降, 而氮同位素富集Δ15N值则上升。其中全鱼Δ13C从4.19‰分别下降到3.94‰和3.63‰, 肌肉Δ13C从4.46‰分别下降到3.98‰和3.67‰; 全鱼Δ15N从0.18‰分别增加到0.88‰和0.94‰, 肌肉Δ15N从0.18‰分别增加到0.74‰和0.87‰。军曹鱼在摄食3种不同蛋白源饲料时, 其全鱼和肌肉的Δ13C和Δ15N的变化趋势相似, 但全鱼δ15N的变化速度慢于肌肉。据此可推断, 肌肉可在生态学营养级研究(长时间尺度)中代表军曹鱼的碳、氮同位素特征; 但在代谢生理学研究中(短时间尺度), 肌肉就无法准确反映军曹鱼全鱼的δ15N变化过程。
In order to investigate the effects of different diet protein sources on carbon and nitrogen isotope fractionation of juvenile cobia Rachycentron canadum L., three isonitrogenous and isocaloric diets were formulated. The protein source in D1 was fish meal; beer yeast meal and corn gluten meal protein replaced 10% fish meal in D2 and D3, respectively. The diets were fed to juvenile cobia for 24 days. The results showed that, when 10% fish meal was replaced, the weight gain rate (WGR) of cobia decreased significantly. The carbon isotope ratio δ13C of cobia increased in time and nitrogen isotope ratio δ15N decreased in time in all groups. Although the change speeds of δ15N were different, the whole fish and muscle of cobia fed with different diets reached isotope equilibrium states with their diets when the feeding experiment was accomplished. When 10% fish meal was replaced by beer yeast meal (corn gluten meal) protein, the carbon isotope fractionation Δ13C decreased while nitrogen isotope fractionation Δ15N increased in the whole fish and muscle of cobia; Δ13C of the whole fish decreased from 4.19‰ to 3.94‰ and 3.63‰, Δ13C of the muscle decreased from 4.46‰ to 3.98‰ (to 3.67‰), and Δ15N of the whole fish increased from 0.18‰ to 0.88‰ (to 0.94‰), Δ15N of the muscle increased from 0.18‰ to 0.74‰ (to 0.87‰). When the three diets with different protein sources were fed, the variation trends of Δ13C and Δ15N were similar between whole fish and muscle of cobia, but the change speed of whole fish δ15N was slower than that of muscle. These results indicated that cobia muscle can represent the δ13C and δ15N characters of whole fish in trophic level study of ecosystem (long time scale), but cannot represent the change process of whole fish δ15N in metabolic physiology study (short time scale).
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