Alkaline Environmental pH Has No Effect on Ammonia Excretion in the Mudskipper Periophthalmodon schlosseri but Inhibits Ammonia Excretion in the Related Species Boleophthalmus boddaerti
Experiments were performed to evaluate the effects of alkaline environmental pH on urea and ammonia excretion rates and on tissue urea, ammonia, and free amino acid concentrations in two mudskippers, Periophthalmodon schlosseri and Boleophthalmus boddaerti. Periophthalomodon schlosseri is known to b...
Gespeichert in:
Veröffentlicht in: | Physiological and biochemical zoology 2003-03, Vol.76 (2), p.204-214 |
---|---|
Hauptverfasser: | , , , , |
Format: | Artikel |
Sprache: | eng |
Schlagworte: | |
Online-Zugang: | Volltext |
Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
Zusammenfassung: | Experiments were performed to evaluate the effects of alkaline environmental pH
on urea and ammonia excretion rates and on tissue urea, ammonia, and free amino
acid concentrations in two mudskippers, Periophthalmodon
schlosseri and Boleophthalmus boddaerti.
Periophthalomodon schlosseri is known to be capable of
actively excreting ammonia. The rate of ammonia excretion in B.
boddaerti exposed to 50% seawater (brackish water, BW) at pH 9
decreased significantly during the first 2 d of exposure when compared with that
of specimens exposed to pH 7 or 8. This suggested that B.
boddaerti was dependent on NH3 diffusion for ammonia
excretion, as in most fishes. It was incapable of detoxifying the accumulating
endogenous ammonia to urea but could store and tolerate high concentrations of
ammonia in the muscle, liver, and plasma. It did not undergo reductions in
proteolysis and/or amino acid catabolism in alkaline water, probably because the
buildup of endogenous ammonia was essential for the recovery of the normal rate
of ammonia excretion by the third day of exposure to a pH 9 medium. Unlike
B. boddaerti, P. schlosseri did not
accumulate ammonia in the body at an alkaline pH (i.e., pH 9) because it was
capable of actively excreting ammonia. Periophthalmodon
schlosseri did not undergo partial amino acid catabolism (no
accumulation of alanine) either, although there might be a slight reduction in
amino acid catabolism in general. The significant decrease in blood
pCO2 in B. boddaerti at pH 9 might lead to
respiratory alkalosis in the blood. In contrast, P. schlosseri
was able to maintain its blood pH in BW at pH 9 despite a decrease in
pCO2 in the blood. With 8 mM NH4Cl in BW at pH 7, both
mudskippers could actively excrete ammonia, although not to the same extent.
Only P. schlosseri could sustain ammonia excretion against 8 mM
NH4Cl in BW at pH 8. In BW containing 8 mM NH4Cl at pH
9, both mudskippers died within a short period of time. Boleophthalmus
boddaerti consistently died faster than did P.
schlosseri. This indicates that the body surfaces of these
mudskippers were permeable to NH3, but the skin of P.
schlosseri might be less permeable to NH3 than that of
B. boddaerti. Both mudskippers excreted acid
(H+) to alter the pH of the alkaline external medium. Such a
capability, together with modifications in gill morphology and morphometry as in
P. schlosseri, might be essential to the development of an
effective mechanism for the active excretion of
\documentclass{ |
---|---|
ISSN: | 1522-2152 1537-5293 |
DOI: | 10.1086/374281 |