Hatchery-reared coho salmon develop less otolith deformities in tanks with alternating water flow directions
Bibliographic record
Abstract
Hatchery-reared salmonids frequently develop vateritic otoliths—abnormal calcium carbonate structures that impair hearing, balance, and survival. Although vaterite formation has been linked to artificial rearing conditions, the influence of water flow direction has been largely overlooked. This study investigated how tank water flow direction affects otolith composition, asymmetry, and survival to adult return (SAR) in hatchery-reared coho salmon ( Oncorhynchus kisutch ). Fish were reared in circular tanks under three water flow regimes: clockwise (unidirectional), counterclockwise (unidirectional), or alternating (reversed every seven days). Vaterite coverage and otolith asymmetry were assessed via sagittal otolith analysis, and SAR was tracked using passive integrated transponder (PIT) tags. Fish reared under alternating flow had significantly lower vaterite formation and fewer asymmetrical otolith pairs compared to unidirectional flow treatments. While SAR did not differ significantly among treatments, survival estimates were highest in the alternating flow group. These findings suggest that water flow direction is a simple, widely applicable hatchery-rearing modification that may reduce otolith deformities, enhance fish welfare, and improve post-release outcomes. Given the widespread use of unidirectional flow in hatcheries and the high prevalence of vateritic otoliths in hatchery-reared salmonids, alternating flow may help mitigate vaterite-related sensory impairments and contribute to more effective conservation and stock enhancement programs across species and systems. • Alternating water flow reduces vateritic otolith formation in hatchery coho salmon. • Otolith asymmetries are significantly lower under alternating flow conditions. • Unidirectional flow leads to side-specific otolith deformities in circular tanks. • Alternating flow may enhance fish welfare and improve post-release survival. • Flow direction is a simple, low-cost enrichment applicable across hatchery systems.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 teacher head, 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".