DataSheet1_Understanding how high stocking densities and concurrent limited oxygen availability drive social cohesion and adaptive features in regulatory growth, antioxidant defense and lipid metabolism in farmed gilthead sea bream (Sparus aurata).PDF

The study combined the use of biometric, behavioral, physiological and external tissue damage scoring systems to better understand how high stocking densities drive schooling behavior and other adaptive features during the finishing growing phase of farmed gilthead sea bream in the Western Mediterranean. Fish were grown at three different final stocking densities (LD, 8.5 kg/m3; MD, 17 kg/m3; HD, 25 kg/m3). Water oxygen concentration varied between 5 and 6 ppm in LD fish to 3–4 ppm in HD fish with the summer rise of water temperature from 19°C to 26°C (May–July). HD fish showed a reduction of feed intake and growth rates, but they also showed a reinforced social cohesion with a well-defined endogenous swimming activity rhythm with feeding time as a main synchronization factor. The monitored decrease of the breathing/swimming activity ratio by means of the AEFishBIT data-logger also indicated a decreased energy partitioning for growth in the HD environment with a limited oxygen availability. Plasma glucose and cortisol levels increased with the rise of stocking density, and the close association of glycaemia with the expression level of antioxidant enzymes (mn-sod, gpx4, prdx5) in liver and molecular chaperones (grp170, grp75) in skeletal muscle highlighted the involvement of glucose in redox processes via rerouting in the pentose-phosphate-pathway. Other adaptive features included the depletion of oxidative metabolism that favored lipid storage rather than fatty acid oxidation to decrease the oxygen demand as last electron acceptor in the mitochondrial respiratory chain. This was coincident with the metabolic readjustment of the Gh/Igf endocrine-growth cascade that promoted the regulation of muscle growth at the local level rather than a systemic action via the liver Gh/Igf axis. Moreover, correlation analyses within HD fish displayed negative correlations of hepatic transcripts of igf1 and igf2 with the data-logger measurements of activity and respiration, whereas the opposite was found for muscle igf2, ghr1 and ghr2. This was indicative of a growth-regulatory transition that supported a proactive instead of a reactive behavior in HD fish, which was considered adaptive to preserve an active and synchronized feeding behavior with a minimized risk of oxidative stress and epidermal skin damage.

本研究结合生物特征、行为学、生理学及外部组织损伤评分系统，旨在深入解析西地中海养殖金头鲷（gilthead sea bream）育成后期高放养密度对其集群行为及其他适应性特征的影响机制。实验设置3种最终放养密度：低密度组（LD, 8.5 kg/m³）、中密度组（MD, 17 kg/m³）及高密度组（HD, 25 kg/m³）。在夏季水温从19℃升至26℃（5月至7月）期间，低密度组水体溶氧浓度介于5~6 ppm，高密度组则降至3~4 ppm。高密度组金头鲷的摄食量与生长速率均出现下降，但同时其社群凝聚力增强，呈现出明确的内源性游泳活动节律，且摄食时间为该节律的主要同步因子。通过AEFishBIT数据记录仪监测到的呼吸/游泳活动比下降，也表明在溶氧有限的高密度环境中，鱼类用于生长的能量分配有所减少。血浆葡萄糖与皮质醇水平随放养密度升高而上升；血糖浓度与肝脏中mn-sod、gpx4、prdx5等抗氧化酶以及骨骼肌中grp170、grp75等分子伴侣的表达水平密切相关，这提示葡萄糖可通过磷酸戊糖途径的代谢重定向参与氧化还原过程。其他适应性特征包括氧化代谢的减弱：相较于脂肪酸氧化，脂质储存更占优势，以此降低作为线粒体呼吸链最终电子受体的氧气消耗。这一现象与Gh/Igf内分泌生长级联反应的代谢重调控相契合，该调控促进了肌肉生长的局部调节，而非通过肝脏Gh/Igf轴发挥全身作用。此外，对高密度组个体的相关性分析显示，肝脏中igf1与igf2的转录本水平与数据记录仪测得的活动及呼吸参数呈负相关，而肌肉中igf2、ghr1及ghr2则呈现相反的相关性。这表明高密度环境下鱼类的生长调控发生转变，支持其采取主动而非被动的行为模式，该适应性策略有助于维持活跃且同步的摄食行为，同时将氧化应激与表皮皮肤损伤的风险降至最低。