Effects of formalin preservation on egg size of small pelagic fish as major target species in ichthyoplankton surveys

Abstract Preservation is critical for egg and larval samples from ichthyoplankton surveys. As growing interest is directed toward maternal effects on egg quality, historical collections of egg samples in formalin are potentially invaluable materials but concerns about the effects of formalin preservation need to be clarified. The present study examined effects of formalin preservation on egg size of Japanese sardine Sardinops melanostictus , chub mackerel Scomber japonicus and Japanese anchovy Engraulis japonicus over a long period (30–36 months). Overall, the egg sizes slightly decreased in a couple of months after preservation but then recovered to be at a similar level to the live eggs for diameters of spherical eggs of sardine and mackerel and short diameters of ellipsoidal eggs of anchovy, although a caveat lies in unstable and slightly increasing patterns in long diameters of anchovy eggs. No substantial differences were found between 5% and 10% formalin solutions. For practical purposes, we conclude that no correction factors are required for using the measurements of egg samples preserved in formalin over a long period. Assuming the applicability to congeneric species, the information presented here supports the validity of previous studies and will promote future studies on egg size variability in small pelagic fish based on historical collections of egg samples preserved in formalin in various regions of the world.