Ion levels in the gastrointestinal tract content of freshwater and marine-estuarine teleosts.

This study investigated the relationship between ion levels (Na⁺, Cl⁻, K⁺, Ca²âº, and Mg²âº) in the fluid phase and total chyme of the contents of the gastrointestinal tract segments of freshwater and marine-estuarine teleosts collected in different salinities (0-34 ppt) in estuarine and freshwater portions of the São Gonçalo channel, southern Brazil. In addition, the relative contribution of feeding and osmoregulation to the ionic content of each portion of the gastrointestinal tract of fishes collected in different ambient salinities was analyzed. There was no relationship between salinity and ion levels in the fluid phase and total chyme of the segments of the gastrointestinal tract when considering all species together. However, there was a significant positive relationship between salinity and ion levels in the fluid phase and total chyme of two fish species (Micropogonias furnieri and Genidens barbus) collected in three or more different salinities. In most species, ion levels in the fluid phase and total chyme changed throughout the gastrointestinal tract, suggesting absorption, but the ionoregulatory mechanisms of the gastrointestinal tract seem to vary according to species.

Plasma ion levels of freshwater and marine/estuarine teleosts from Southern Brazil

The purpose of this study was to investigate Na+, Cl-, K+, Ca2+, and Mg2+ levels in the plasma of freshwater and marine/estuarine teleosts collected at different salinities (0 to 34) from the estuarine and freshwater portions of the São Gonçalo channel in Southern Brazil. Any relationship between plasma ion levels and salinity and the capacity of ionic regulation of teleosts found at three or more different salinities (Genidens barbus and Micropogonias furnieri) was also investigated. Results showed no relationship between plasma ion levels and salinity when considering all species together, but the two species collected from three or more different salinities showed a significant positive relationship between plasma ion levels and salinity, indicating that G. barbus and M. furnieri have a high capacity to regulate plasma ion levels at both low and high salinities.

A proposta deste estudo foi investigar os níveis de Na+, Cl-, K+, Ca2+, and Mg2+ no plasma de teleósteos de água doce e marinhos/estuarinos coletados em diferentes salinidades (0 a 34) nas porções de água doce e estuarinas do Canal São Gonçalo, sul do Brasil. Uma possível relação entre os níveis iônicos plasmáticos e a salinidade também foi investigada bem como a capacidade de regulação iônica dos teleósteos coletados em três ou mais salinidades (Genidens barbus e Micropogonias furnieri). Os resultados mostraram que não houve relação entre os níveis iônicos no plasma com a salinidade quando considerando todas as espécies juntas, mas as duas espécies coletadas em três ou mais salinidades mostraram uma relação significativamente positiva entre níveis iônicos no plasma e salinidade, mostrando que G. barbus e M. furnieri apresentaram uma grande capacidade para regular os íons do plasma em baixas e altas salinidades.