Bamfield Marine Sciences Center, 100 Pachena Road, Bamfield, BC, V0R 1B0, Canada.
J Comp Physiol B. 2011 Jul;181(5):615-30. doi: 10.1007/s00360-011-0550-x. Epub 2011 Jan 28.
Recent studies focusing on the consequences of feeding for ion and water balance in freshwater fish have revealed the need for similar comparative studies in seawater fish. A detailed time course sampling of gastrointestinal (GI) tract contents following the ingestion of a single meal of a commercial diet revealed the assimilation of both water and dietary ions (Na(+), Cl(-), K(+), Ca(2+), Mg(2+)) along the GI tract of seawater-acclimated rainbow trout (Oncorhynchus mykiss) which had been fasted for 1 week. Consumption of the meal did not change the drinking rate. There was a large secretion of fluid into the anterior intestine and caecae (presumably bile and/or pancreatic secretions). As a result, net assimilation (63%) of the ingested water along the GI tract was lower than generally reported for fasted trout. Mg(2+) was neither secreted into nor absorbed from the GI tract on a net basis. Only K(+) (93% assimilated) and Ca(2+) (43% assimilated) were absorbed in amounts in excess of those provided by ingested seawater, suggesting that dietary sources of K(+) and Ca(2+) may be important to seawater teleosts. The oesophagus-stomach served as a major site of absorption for Na(+), Cl(-), K(+), Ca(2+), and Mg(2+), and the anterior intestine and caecae as a major site of net secretion for all of these ions, except Cl(-). Despite large absorptive fluxes of these ions, the ionic composition of the plasma was maintained during the digestion of the meal. The results of the present study were compared with previous work on freshwater-acclimated rainbow trout, highlighting some important differences, but also several similarities on the assimilation of water and ions along the gastrointestinal tract during digestion. This study highlights the complicated array of ion and water transport that occurs in the intestine during digestion while revealing the importance of dietary K(+) and Ca(2+) to seawater-acclimated rainbow trout. Additionally, this study reveals that digestion in seawater-acclimated rainbow trout appears to compromise intestinal water absorption.
最近的研究集中在摄食对淡水鱼类离子和水平衡的影响，揭示了需要对海水鱼类进行类似的比较研究。对空腹 1 周的海水驯化虹鳟鱼（Oncorhynchus mykiss）单次摄食商业饲料后整个胃肠道（GI）内容物进行详细的时间进程采样，发现水和膳食离子（Na(+), Cl(-), K(+), Ca(2+), Mg(2+))在整个胃肠道被同化，摄食并未改变其饮水率。大量液体分泌到前肠和盲肠（推测为胆汁和/或胰液分泌）。因此，与通常报道的空腹虹鳟鱼相比，沿胃肠道对摄入水的净同化（63%）较低。Mg(2+)在胃肠道内既不分泌也不吸收。只有 K(+)（93%同化）和 Ca(2+)（43%同化）的吸收量超过了摄入海水的含量，这表明 K(+)和 Ca(2+)的膳食来源对海水硬骨鱼可能很重要。食道-胃是 Na(+), Cl(-), K(+), Ca(2+)和 Mg(2+)吸收的主要部位，前肠和盲肠是除 Cl(-)外所有这些离子净分泌的主要部位。尽管这些离子的吸收通量很大，但在摄食过程中血浆的离子组成仍得以维持。本研究的结果与以前关于淡水驯化虹鳟的研究进行了比较，突出了一些重要的差异，但也有一些在消化过程中沿胃肠道同化水和离子的相似之处。本研究强调了在消化过程中肠道内发生的复杂离子和水转运，但也揭示了膳食 K(+)和 Ca(2+)对海水驯化虹鳟的重要性。此外，本研究表明，海水驯化虹鳟的消化似乎会损害肠道的水吸收。
