Nebel Catherine, Romestand Bernard, Nègre-Sadargues Geneviève, Grousset Evelyse, Aujoulat Fabien, Bacal Julien, Bonhomme François, Charmantier Guy
Laboratoire Génome, Populations, Interactions, Adaptation, UMR 5171, Université Montpellier II, Place E. Bataillon, 34095 Montpellier, Cedex 05, France.
J Exp Biol. 2005 Oct;208(Pt 20):3859-71. doi: 10.1242/jeb.01853.
The effects of long-term freshwater acclimatization were investigated in juvenile sea-bass Dicentrarchus labrax to determine whether all sea-bass juveniles are able to live in freshwater and to investigate the physiological basis of a successful adaptation to freshwater. This study particularly focused on the ability of sea-bass to maintain their hydromineral balance in freshwater and on their ion (re)absorbing abilities through the gills and kidneys. Two different responses were recorded after a long-term freshwater acclimatization. (1) Successfully adapted sea-bass displayed standard behavior; their blood osmolality was maintained almost constant after the freshwater challenge, attesting to their efficient hyperosmoregulation. Their branchial and renal Na+/K+-ATPase abundance and activity were high compared to seawater fish due to a high number of branchial ionocytes and to the involvement of the urinary system in active ion reabsorption, producing hypotonic urine. (2) Sea-bass that had not successfully adapted to freshwater were recognized by abnormal schooling behavior. Their blood osmolality was low (30% lower than in the successfully adapted sea-bass), which is a sign of acute osmoregulatory failure. High branchial Na+/K+-ATPase abundance and activity compared to successfully adapted fish were coupled to a proliferation of gill chloride cells, whose ultrastructure did not display pathological signs. The large surface used by the gill chloride cells might negatively interfere with respiratory gas exchanges. In their urinary system, enzyme abundance and activity were low, in accordance with the observed lower density of the kidney tubules. Urine was isotonic to blood in unsuccessfully adapted fish, ruling out any participation of the kidney in hyperosmoregulation. The kidney failure seems to generate a compensatory ion absorption through increased gill activity, but net ion loss through urine seems higher than ion absorption by the gills, leading to lower hyper-osmoregulatory performance and to death.
研究了幼体海鲈（欧洲鲈）长期适应淡水的影响，以确定所有幼体海鲈是否都能在淡水中生存，并探究成功适应淡水的生理基础。本研究特别关注海鲈在淡水中维持其水盐平衡的能力，以及它们通过鳃和肾脏进行离子（再）吸收的能力。长期适应淡水后记录到两种不同的反应。（1）成功适应的海鲈表现出正常行为；在接受淡水挑战后，它们的血液渗透压几乎保持恒定，证明其有效的高渗调节能力。与海水鱼相比，它们的鳃和肾脏钠钾ATP酶的丰度和活性较高，这是由于鳃离子细胞数量众多以及泌尿系统参与主动离子重吸收，从而产生低渗尿液。（2）未成功适应淡水的海鲈表现为异常的集群行为。它们的血液渗透压较低（比成功适应的海鲈低30%），这是急性渗透调节失败的迹象。与成功适应的鱼相比，其鳃钠钾ATP酶的丰度和活性较高，同时鳃氯细胞增殖，其超微结构未显示病理迹象。鳃氯细胞使用的大表面积可能会对呼吸气体交换产生负面影响。在它们的泌尿系统中，酶的丰度和活性较低，这与观察到的肾小管密度较低一致。未成功适应的鱼的尿液与血液等渗，排除了肾脏参与高渗调节的可能性。肾衰竭似乎通过增加鳃的活性产生代偿性离子吸收，但通过尿液的净离子损失似乎高于鳃的离子吸收，导致高渗调节性能降低并最终死亡。
