title: Nitrogen metabolism in tambaqui (Colossoma macropomum), a neotropical model teleost: hypoxia, temperature, exercise, feeding, fasting, and high environmental ammonia.
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-Nand ~39 % of MUrea-Nvia 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-Nduring and after 48-h exposure to 2.5 mmol L-1HEA. 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-Ndeclined, and recovered thereafter, similar to the response seen in other hypoxia-tolerant teleosts; MUrea-Ndid not change. However, during gradual hypoxia, MAmm-Nremained constant, but MUrea-Neventually fell. The acute temperature sensitivities of MAmm-Nand MNwere low from 28 °C (acclimation) to 33 °C (Q10 ~1.5), but high (~3.8) from 33 to 38 °C, relative to [Formula: see text] (~1.9 throughout). In contrast, MUrea-Nexhibited 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, [Formula: see text] and MUrea-Nincreased 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-Npeaked at 4-6 h, and MUrea-Nat 6-9-h post-feeding, with an additional peak in MAmm-Nonly at 21 h. During subsequent fasting, MNstabilized 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.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. woodcm@zoology.ubc.ca.|Department of Biology, McMaster University, Hamilton, ON, Canada. woodcm@zoology.ubc.ca.|Rosenstiel School of Marine and Atmospheric Science, University of Miami, Coral Gables, FL, USA. woodcm@zoology.ubc.ca.|Laboratório de Ecofisiologia e Evolução Molecular, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas, Brazil. woodcm@zoology.ubc.ca.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Wood
authors.affiliation: Laboratório de Ecofisiologia e Evolução Molecular, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas, Brazil.
authors.forename: José Gadelha
authors.initials: JG
authors.lastname: de Souza Netto
authors.affiliation: Laboratório de Ecofisiologia e Evolução Molecular, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas, Brazil.|Laboratório de Fisologia Molecular, Centro Interdisciplinar de Investigação Marinha e Ambiental, Porto, Portugal.|Department of Biology, Wilfrid Laurier University, Waterloo, ON, Canada.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Wilson
authors.affiliation: Laboratório de Ecofisiologia e Evolução Molecular, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas, Brazil.|Instituto de Biociências, Universidade do Estado de São Paulo, Campus do Litoral Paulista, Sao Vicente, SP, Brazil.
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Duarte
authors.affiliation: Laboratório de Ecofisiologia e Evolução Molecular, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas, Brazil.
authors.forename: Adalberto Luis
authors.initials: AL
authors.lastname: Val
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D060125:Characiformes / Q000378:metabolism*; D004777:Environment; D005247:Feeding Behavior; D005880:Gills / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal; D013696:Temperature; D014508:Urea / Q000378:metabolism
chemical_list: D000641:Ammonia; D014508:Urea; D009584:Nitrogen
keywords: Ammonia; Endogenous fraction; Exogenous fraction; Nitrogen quotient; Oxygen consumption; Protein; Transepithelial potential; Urea