Changes in size of European hake larvae and conversion factors for different preservation mediums

Abstract

The objective of this study was to determine how preservation methods affect the standard length (SL, mm) of European hake larvae. We used five fixative methods: (i) freezing in seawater at −20°C; (ii) RNAlater at −80°C; (iii) 4% borax-buffered formalin; (iv) freezing with liquid nitrogen and (v) 95% ethanol. Standard length hake larvae were initially measured and individually fixed in each of the five fixatives. To evaluate the effect of the time preserved in each one, we obtained the SL of larvae for a second time after three different preservation periods: 15, 44 and 91 days. To assess the effect of initial size on final shrinkage, we analysed two groups of larvae born in captivity, 15 and 24 days post hatching respectively. Most shrinkage occurred within the first period of preservation in all fixatives, the preservation time having no effect on the percentage of shrinkage for any preservative. However, initial SL affects the percentage of shrinkage depending on the fixative used. We suggest five correlation equations to convert an initial SL into a final contracted size of hake larvae for each fixative.