Nitrogen metabolism in tambaqui (Colossoma macropomum), a neotropical model teleost: hypoxia, temperature, exercise, feeding, fasting, and high environmental ammonia
The total rate of N-waste excretion ( M N ) in juvenile tambaqui living in ion-poor Amazonian water comprised 85 % ammonia-N ( M Amm-N ) and 15 % urea-N ( M Urea-N ). Both occurred mainly across the gills with only ~5 % of M Amm-N and ~39 % of M Urea-N via the urine. Tambaqui were not especially tol...
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| Published in: | Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 187; no. 1; pp. 135 - 151 |
|---|---|
| Main Authors: | , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Berlin/Heidelberg
Springer Berlin Heidelberg
2017
Springer Nature B.V |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | The total rate of N-waste excretion (
M
N
) in juvenile tambaqui living in ion-poor Amazonian water comprised 85 % ammonia-N (
M
Amm-N
) and 15 % urea-N (
M
Urea-N
). Both occurred mainly across the gills with only ~5 % of
M
Amm-N
and ~39 % of
M
Urea-N
via the urine. Tambaqui were not especially tolerant to high environmental ammonia (HEA), despite their great resistance to other environmental factors. Nevertheless, they were able to maintain a continued elevation of
M
Amm-N
during and after 48-h exposure to 2.5 mmol L
−1
HEA. The normally negative transepithelial potential (−18 mV) increased to −9 mV during the HEA period, which would help to reduce branchial NH
4
+
entry. During 3 h of acute environmental hypoxia (30 % saturation),
M
Amm-N
declined, and recovered thereafter, similar to the response seen in other hypoxia-tolerant teleosts;
M
Urea-N
did not change. However, during gradual hypoxia,
M
Amm-N
remained constant, but
M
Urea-N
eventually fell. The acute temperature sensitivities of
M
Amm-N
and
M
N
were low from 28 °C (acclimation) to 33 °C (Q10 ~1.5), but high (~3.8) from 33 to 38 °C, relative to
M
O
2
(~1.9 throughout). In contrast,
M
Urea-N
exhibited a different pattern over these temperature ranges (Q10 2.6 and 2.1, respectively). The nitrogen quotient (NQ = 0.16–0.23) was high at all temperatures, indicating a 60–85 % reliance on protein to fuel aerobic metabolism in these fasting animals. During steady-state aerobic exercise,
M
O
2
and
M
Urea-N
increased in parallel with velocity (up to 3.45 body lengths s
−1
), but
M
Amm
(and thus
M
N
) remained approximately constant. Therefore, the NQ fell progressively, indicating a decreasing reliance on protein-based fuels, as work load increased. In group feeding trials using 45 % protein commercial pellets, tambaqui excreted 82 % (range 39–170 %) of the dietary N within 24 h; N-retention efficiency was inversely related to the ration voluntarily consumed.
M
Amm-N
peaked at 4–6 h, and
M
Urea-N
at 6–9-h post-feeding, with an additional peak in
M
Amm-N
only at 21 h. During subsequent fasting,
M
N
stabilized at a high endogenous rate from 2 through 8 days post-feeding. Possible reasons for the high wasting of protein-N during both fasting and feeding are discussed. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0174-1578 1432-136X |
| DOI: | 10.1007/s00360-016-1027-8 |