A control diameter rule cut mean squared speed error by 96% for ten selected mutant Mauthner axons in zebrafish

We tested whether axon diameter predicts reported conduction speed across a genetic change. We used paired measurements from Bin et al. (2024), with one Mauthner axon per larval zebrafish. Rules were fitted to 18 controls at days 3 to 5. All ten selected day-5 neuron-specific ipo13b mutants stayed out of fitting. A diameter rule reduced mutant mean squared speed error from 0.21716 to 0.009379 (m/s)^2 relative to an age rule, a decrease of 95.68%. The central 95% range from 9,999 fish bootstrap samples with complete model fitting was 87.65% to 98.73%. Diameter also reduced error relative to separate age means and a constant. Yet diameter did not beat age in control leave-one-fish-out tests. Proportional and square-root diameter rules gave nearly equal mutant errors. Single-age free-intercept fits were unstable. Thus, transfer performance did not select a general speed law. For a common 1 mm path, calculated delay MSE fell by 91.26%. This was not a new delay measurement. The test extends the source result with an explicit transfer benchmark; it is not independent biological replication. Mutants were selected for reduced diameter, clutch labels were absent, and the sample covers one neuron class. Fish resampling assumes independence within source groups. The package preserves the source workbook, source-cell addresses, code, all predictions and bootstrap draws, figures, independent checks and repeat instructions.

axon diameter · conduction speed · Mauthner neuron · zebrafish · transfer prediction · connectome timing · ipo13b