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<p>In surveys of larval fish, samples are often collected by net and fixed with ethanol immediately after collection; thereafter they shrink from dehydration. Because body length (BL) is basic information for larval studies, a procedure to estimate pre-fixed BLs is required. Here, we present the degree of shrinkage and practical regression models to estimate pre-fixed BL from post-fixed measurements of larvae of 20 simultaneously collected fish taxa smaller than 15&#xa0;mm by comparing pre-fixed BLs with BLs of the same individuals after fixation in 99.5% ethanol. The shrinkage of BL varied between 4.6 and 10.3% among the taxa. Ethanol fixation induces length-dependent shrinkage in larval fish. Multiple regression analysis revealed no change in slope at the 20 fish taxa, and a slight difference was detected in the intercept at six fish taxa. A linear regression model (slope = 1.017, intercept = 0.347) accurately predicted pre-fixed BL from post-fixed measurements, with minor variations among taxa (R<sup>2</sup>: 0.941–0.997). Of these 20 fish taxa, 13 were examined for changes in shrinkage with developmental stage, four taxa showed a tendency of less shrinkage with the progression of developmental stage. These results suggested that the shrinkage of larvae after ethanol fixation was greatly influenced by the pre-fixed BL, and our results provide practical conversion equations for larval studies, enhancing the accuracy of body-length estimations in ethanol-fixed samples.</p>

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Shrinkage of ethanol-fixed fish larvae and conversion to pre-fixed body size in simultaneously collected larval assemblages

  • 期刊论文

  • 发表日期：

    2025年11月12日

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  • Taiki Ishihara,
  • Yosuke Tanaka,
  • Atsushi Tawa

摘要

In surveys of larval fish, samples are often collected by net and fixed with ethanol immediately after collection; thereafter they shrink from dehydration. Because body length (BL) is basic information for larval studies, a procedure to estimate pre-fixed BLs is required. Here, we present the degree of shrinkage and practical regression models to estimate pre-fixed BL from post-fixed measurements of larvae of 20 simultaneously collected fish taxa smaller than 15 mm by comparing pre-fixed BLs with BLs of the same individuals after fixation in 99.5% ethanol. The shrinkage of BL varied between 4.6 and 10.3% among the taxa. Ethanol fixation induces length-dependent shrinkage in larval fish. Multiple regression analysis revealed no change in slope at the 20 fish taxa, and a slight difference was detected in the intercept at six fish taxa. A linear regression model (slope = 1.017, intercept = 0.347) accurately predicted pre-fixed BL from post-fixed measurements, with minor variations among taxa (R2: 0.941–0.997). Of these 20 fish taxa, 13 were examined for changes in shrinkage with developmental stage, four taxa showed a tendency of less shrinkage with the progression of developmental stage. These results suggested that the shrinkage of larvae after ethanol fixation was greatly influenced by the pre-fixed BL, and our results provide practical conversion equations for larval studies, enhancing the accuracy of body-length estimations in ethanol-fixed samples.