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Title: | Nitrogen metabolism in tambaqui (Colossoma macropomum), a neotropical model teleost: hypoxia, temperature, exercise, feeding, fasting, and high environmental ammonia |
Authors: | Wood, Chris M. Souza Netto, José Gadelha de Wilson, Jonathan Duarte, Rafael Mendonça Val, Adalberto Luis |
Keywords: | Ammonia Nitrogen Urea Animals Animals Experiment Characiformes Environment Feeding Behavior Gill Hypoxia Kidney Metabolism Oxygen Consumption Temperature Ammonia Animal Characiformes Environment Feeding Behavior Gills Hypoxia Kidney Nitrogen Oxygen Consumption Physical Conditioning, Animals Temperature Urea |
Issue Date: | 2017 |
metadata.dc.publisher.journal: | Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology |
metadata.dc.relation.ispartof: | Volume 187, Número 1, Pags. 135-151 |
Abstract: | The total rate of N-waste excretion (MN) in juvenile tambaqui living in ion-poor Amazonian water comprised 85 % ammonia-N (MAmm-N) and 15 % urea-N (MUrea-N). Both occurred mainly across the gills with only ~5 % of MAmm-N and ~39 % of MUrea-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 MAmm-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 NH4 + entry. During 3 h of acute environmental hypoxia (30 % saturation), MAmm-N declined, and recovered thereafter, similar to the response seen in other hypoxia-tolerant teleosts; MUrea-N did not change. However, during gradual hypoxia, MAmm-N remained constant, but MUrea-N eventually fell. The acute temperature sensitivities of MAmm-N and MN were low from 28 °C (acclimation) to 33 °C (Q10 ~1.5), but high (~3.8) from 33 to 38 °C, relative to MO2 (~1.9 throughout). In contrast, MUrea-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, MO2 and MUrea-N increased in parallel with velocity (up to 3.45 body lengths s−1), but MAmm (and thus MN) 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. MAmm-N peaked at 4–6 h, and MUrea-N at 6–9-h post-feeding, with an additional peak in MAmm-N only at 21 h. During subsequent fasting, MN 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. © 2016, Springer-Verlag Berlin Heidelberg. |
metadata.dc.identifier.doi: | 10.1007/s00360-016-1027-8 |
Appears in Collections: | Artigos |
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