Abstract This study assessed both the effectiveness of a physical-mechanical rupture method and the ability of feed additives (phytogenic compounds, alginate oligosaccharide and nucleotides) to enhance the utilization of G. gracilis by European seabass. A commercial-based diet was used as control diet (CTRL) and compared with five isoproteic (53.5% Dry matter, DM) and isolipidic (14.9% DM) diets containing 8% of G. gracilis. This seaweed was either unprocessed (diet GRA) or subjected to physical processing (diet GRAP). The three additive-containing diets were formulated by supplementing the GRA diet with either 0.02% phytogenic compounds (PHY), 2.5% oligo-alginate (OAS) or 0.08% free nucleotides (NUC). Triplicate groups of nineteen fish (29.7 ± 0.02 g) were distributed by 50 L tanks (11.3 kg m−3) and fed the experimental diets to satiety during 106 days. By the end of the trial, growth performance and nutrient utilization (specific growth ratio, feed conversion ratio, apparent digestibility coefficients, nutrient balance, intestinal brush border membrane enzyme activities and plasma metabolic parameters), gut histomorphology, antioxidant and immunological status of fish were evaluated. The ability of fish to digest seaweed-rich diets was largely improved by the technological processing of G. gracilis, albeit nil effect on fish specific growth rate (1.0 in all groups). This major achievement was associated with increased ability of GRAP to digest protein (84 vs 68% in GRA) and energy (64 vs 38% in GRA). The use of feed additives in Gracilaria-rich diets was less efficacious in improving European sea bass nutrient and energy ADCs, but have still improved the overall digestibility of those diets. Fish fed alginate oligosaccharide was mainly associated with increased activity of anterior intestine enzymes, particularly intestinal alkaline phosphatase (IAP; 174.4 vs 104.7–120.6 μm min−1 g−1 in Gracilaria-rich diets). Moreover, the algae technological processing and both the nucleotides and the alginate oligosaccharide seem to have positively affected the intestinal villus width compared to the negative impact seen in fish fed GRA. The tested additives had limited impact on oxidative stress, although glutathione peroxidase (GPx; 2.1 μmol min−1 mg protein−1) and catalase (CAT; 35 μmol min−1 mg protein−1) activities were lowest in fish fed NUC and PHY, respectively. It can be concluded that the physical processing of Gracilaria sp. or the addition of either oligo-alginate or nucleotides can effectively increase the nutritional value of this seaweed for European seabass diets.

中文翻译：

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物理加工或在饲料中添加植物源性化合物、藻酸盐寡糖或核苷酸作为提高欧洲鲈鱼幼鱼 (Dicentrarchus labrax) 对 Gracilaria gracilis 的利用的方法

摘要 本研究评估了物理机械破裂方法的有效性和饲料添加剂（植物性化合物、海藻寡糖和核苷酸）提高欧洲鲈鱼对 G. gracilis 利用率的能力。使用基于商业的饮食作为对照饮食 (CTRL)，并与含有 8% G. gracilis 的五种等蛋白（53.5% 干物质，DM）和等脂（14.9% DM）饮食进行比较。这种海藻要么未经加工（diet GRA），要么经过物理加工（diet GRAP）。通过在 GRA 饮食中添加 0.02% 植物源性化合物 (PHY)、2.5% 低聚藻酸盐 (OAS) 或 0.08% 游离核苷酸 (NUC) 来配制三种含添加剂的饮食。19 条鱼（29.7 ± 0.02 克）的三份重复组由 50 升水箱（11. 3 kg m-3) 并在 106 天期间将实验饮食喂养至饱腹感。试验结束时，鱼类的生长性能和养分利用率（比生长率、饲料转化率、表观消化率、养分平衡、肠道刷状缘膜酶活性和血浆代谢参数）、肠道组织形态学、抗氧化和免疫学状态均在评估。G. gracilis 的技术加工大大提高了鱼类消化富含海藻的饮食的能力，尽管对鱼类的特定生长率没有影响（所有组均为 1.0）。这一重大成就与 GRAP 消化蛋白质（GRA 为 84% 对 68%）和能量（GRA 为 64% 对 38%）的能力增加有关。在富含江蓠的饮食中使用饲料添加剂在改善欧洲鲈鱼的营养和能量 ADC 方面效果较差，但仍然提高了这些饮食的整体消化率。喂食藻酸盐寡糖的鱼主要与前肠酶的活性增加有关，尤其是肠道碱性磷酸酶（IAP；在富含江蓠的饮食中为 174.4 与 104.7–120.6 μm min-1 g-1）。此外，与饲喂 GRA 的鱼的负面影响相比，藻类技术加工以及核苷酸和藻酸盐寡糖似乎对肠绒毛宽度产生了积极影响。测试的添加剂对氧化应激的影响有限，尽管谷胱甘肽过氧化物酶（GPx；2.1 μmol min−1 mg protein−1）和过氧化氢酶（CAT；35 μmol min−1 mg protein−1）活性在饲喂 NUC 和 PHY 的鱼中最低， 分别。可以得出结论，江蓠属的物理加工。