Gills versus kidney for ionoregulation in the obligate air-breathing<i>Arapaima gigas</i>, a fish with a kidney in its air-breathing organ
Bibliographic record
Abstract
In Arapaima gigas, an obligate air-breather endemic to ion-poor Amazonian waters, a large complex kidney runs through the air-breathing organ (ABO). Previous indirect evidence suggested the kidney, relative to the small gills, may be exceptionally important in ionoregulation and N-waste excretion, with support of kidney function by direct O2 supply from the air-space. We tested these ideas by continuous urine collection and gill flux measurements in ∼700g fish. ATPase activities were many-fold greater in kidney than gills. In normoxia, gill Na+ influx and efflux were in balance, with net losses of Cl− and K+. Urine flow rate (UFR, ∼11 ml kg−1 h−1) and urinary ions (< 0.2 mmol L−1) were exceptional, with [urine]/[plasma]ratios of 0.02-0.002 for K+, Na+, and Cl−, indicating strong reabsorption with negligible urinary ion losses. Urinary [ammonia] was very high (10 mmol L−1, [urine]/[plasma] ∼20) indicating strong secretion. The kidney accounted for 21 – 24% of N-excretion, with ammonia dominating (95%) over urea-N through both routes. High urinary [ammonia] was coupled to high urinary [HCO3−]. Aerial hypoxia (15.3 kPa) and aerial hyperoxia (>40.9 kPa) had no effects on UFR, but both inhibited branchial Na+ influx, revealing novel aspects of the osmo-respiratory compromise. Aquatic hypoxia (4.1 kPa), but not aquatic hyperoxia (>40.9 kPa), inhibited gill Na+ influx, UFR and branchial and urinary ammonia excretion. We conclude that the kidney is more important than gills in ionoregulation, and is significant in N-excretion. While not definitive, our results do not indicate direct O2 supply from the ABO for kidney function.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".