The elasmobranch digestive system – current status and future directions
Bibliographic record
Abstract
The gastroenteropancreatic system in elasmobranchs presents a number of firsts in the evolutionary history of vertebrates. This group of fishes were the first to have evolved an acid-pepsin-secreting stomach and demonstrate a glandular pancreas with exocrine and endocrine cells. They additionally were the first to have evolved a well-developed spiral or scroll-like intestine in comparison to the precursor typhlosole - an infolding of the intestinal wall - found in lampreys. Coupled with these features, the unusual metabolic strategy of elasmobranchs is characterized by a lack of reliance on fatty acid oxidation in muscle tissue, and a heavy reliance on ketones and amino acids as metabolic fuels. Further, the ureosmotic strategy of marine elasmobranchs makes them particularly nitrogen limited and thus reliant on regular high-protein meals. Central to these physiological oddities is the gastrointestinal tract (GIT), with absorption of macronutrients and micronutrients being key to maintaining appropriate osmotic balance alongside ensuring continued energy production to fuel somatic growth. Interestingly, the relationship between the physiology of the GIT, energy balance and osmoregulation is only just being explored in elasmobranchs. Here, we review the known processes involved in the assimilation of dietary nutrients in elasmobranchs, from acid digestion to uptake across the spiral intestine. We provide an understanding of the physiological role of accessory organs (gall bladder and pancreas), and we suggest a key role for the (thus far) barely recognised intestinal microbiome in the nitrogen cycle of these fish.
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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 | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.004 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.003 | 0.002 |
| Insufficient payload (model declined to judge) | 0.010 | 0.003 |
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".