季节性变化、昼夜变化和富营养化导致鱼类栖息地周期性缺氧，从而影响商业水产养殖的成功。本研究中，草鱼（Ctenopharyngodon idella）表现出中度耐缺氧性；他们在失去平衡期间表现出中等临界氧张力。在低氧暴露 7 天后，红细胞计数和血红蛋白 (Hb) 浓度显着增加 ( p < 0.01)。为了应对缺氧环境，草鱼经历了鳃重塑，其特征是层间细胞团（ILCM）减少和呼吸表面积增加。细胞凋亡诱导使缺氧下的鳃重塑成为可能。虽然在 ILCM 细胞上未发现凋亡信号，但转移酶 dUTP 缺口末端标记 (TUNEL) 测定结果表明，在缺氧暴露 1 d 后，每个细胞层的 TUNEL 阳性细胞数量增加至 4 d，然后开始减少。与 TUNEL 测定结果一致，凋亡相关基因 caspase-3、Bax和Bcl-2的 mRNA 表达在缺氧处理的第 1、4 和 7 天增加。此外，鳃重塑显着（p < 0.01) 降低了鱼血清中钠离子和氯离子的浓度。这些发现提供了证据，表明草鱼通过鳃丝细胞凋亡来增加其呼吸表面积，从而适应低氧环境。这项研究扩展了我们对草鱼响应缺氧环境的形态和生理变化的理解；因此，它可能有助于维持草鱼的生产。
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Gill remodeling increases the respiratory surface area of grass carp (Ctenopharyngodon idella) under hypoxic stress
Seasonal changes, diurnal variations, and eutrophication result in periodic hypoxia in fish habitats, thus affecting the success of commercial aquaculture. In this study, the grass carp (Ctenopharyngodon idella) presented moderate hypoxia tolerance; they showed a medium critical oxygen tension during the loss of equilibrium. In response to 7 d of hypoxic exposure, the erythrocyte count and hemoglobin (Hb) concentration significantly increased (p < 0.01). To cope with the hypoxic environment, the grass carp underwent gill remodeling marked by reduction in the interlamellar cell mass (ILCM) and an increase in respiratory surface area. The gill remodeling under hypoxia was enabled by apoptosis induction. Although apoptotic signals were not found on ILCM cells, transferase dUTP nick end labeling (TUNEL) assay results indicated that after 1 d of hypoxic exposure, the number of TUNEL-positive cells per lamella increased until 4 d and then began to decrease. Consistent with the results of the TUNEL assay, the mRNA expression of apoptosis-related genes, caspase-3, Bax, and Bcl-2, increased at 1, 4, and 7 d of the hypoxia treatment. In addition, gill remodeling significantly (p < 0.01) decreased the concentration of sodium and chloride ions in the fish serum. These findings provide evidence that grass carps increase their respiratory surface area through gill remodeling by apoptosis in the gill filaments to acclimate to a hypoxic environment. This study expands our understanding of the morphological and physiological changes in grass carp in response to a hypoxic environment; therefore, it could be useful for maintaining grass carp production.