The effects of preservation in 95% ethyl-alcohol and 5% formalin were analysed for 3 months on standard length of Prochilodus lineatus larvae from hatching to the end of the flexion process. Unyolked stages were raised under two feeding regimes: unfed and daily fed. All developmental stages that were preserved in formalin as well as the yolked and flexion-postflexion larvae stored in alcohol shrank significantly (2–6%). In contrast, unyolked preflexion larvae showed a slight but significant enlargement after storage in alcohol (1%). Shrinkage of preflexion stages was 2.5% higher when stored in formalin, while both preservative agents caused similar shrinkage in flexion-postflexion larvae (ca. 3%). Shrinkage levels after storage in alcohol were dependent on live length, decreasing or increasing with increasing length in yolked and flexion-postflexion larvae, respectively. The feeding regime did not affect length changes after preservation in either preservative agent.