Dogmas and controversies in the handling of nitrogenous wastes: The effect of feeding and fasting on the excretion of ammonia, urea and other nitrogenous waste products in rainbow trout
Bibliographic record
Abstract
Ammonia and urea are the primary forms of nitrogen excretion in teleost fish. There exists, however, a discrepancy between the sum of ammonia plus urea nitrogen and total nitrogen, indicating that 'unknown' nitrogen end products may play an important role in nitrogen metabolism. The current study analysed a wide range of nitrogen end products in both fed and fasted juvenile rainbow trout. Ammonia-N (53-68%) and urea-N (6-10%) were confirmed as the most important forms of nitrogenous waste, but an interesting finding was the considerable excretion of nitrogen as amino acids (4-10%), via the gills, and as protein (3-11%), probably via the body mucus. Use of anal sutures delineated an important role for the gastrointestinal tract in the production of ammonia-N and urea-N in fed fish, but amino acid-N and protein-N output by this route were both negligible. Alternative nitrogen products - trimethylamine, trimethylamine oxide, uric acid, and nitrite + nitrate - were not excreted in detectable quantities. Creatine-N and creatinine-N outputs were detected but contributed only a small fraction to total nitrogen excretion (<1.4%). Despite the wide scope of nitrogenous end products investigated, a considerable proportion (12-20%) of nitrogen excretion remains unknown. Possible alternative end products and methodological considerations are proposed to explain this phenomenon. The findings described above were used to recalculate the nitrogen quotient (NQ=(N)/(O(2))) on trout that had been either fasted or fed various daily rations (1%, 3% or 5% dry food per unit wet body mass per day). Feeding increased oxygen consumption ((O(2))) and total-N excretion ((N)). The NQ is often used as a measure of protein utilisation in aerobic metabolism and assumes that all protein (and amino acid) fuels are converted by oxidation to nitrogenous waste products that are excreted. However, the results showed that calculation of the NQ based on total nitrogen excretion may overestimate protein utilisation in aerobic metabolism because of significant excretion of N in the form of proteins and amino acids, whereas the use of summed ammonia-N and urea-N excretion probably underestimates the contribution of protein towards aerobic metabolism. These errors increase as ration increases, because the discrepancy between total-N excretion and ammonia-N + urea-N excretion increases.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.020 | 0.011 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.007 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".