OPTIMIZING EGG COLLECTION METHODS FOR FATHEAD MINNOWS Pimephales promelas

Fathead minnows (Pimephales promelas) are commonly used for laboratory research studies  of reproductive fecundity , quantified as egg number, embryo viability, and larval feeding success. However, the methods of egg collection can impact these outcomes, independent of experimental conditions. Therefore , we tested different methods of initial egg collection to determine best practices in support of fathead minnow reproductive studies.

In culture, adult  fathead  minnow females lay their eggs on the underside of "spawning huts" that are coated with sand to provide a rough surface that facilitates egg adherence during spawning.  M ales then clean and guard the eggs through hatching, which takes  approximately  four days at 25 °C (Figure 1).

However, for research,  eggs are  usually collected within a few hours of fertilization, a process that  prematurely separates eggs from the hut  using manual or chemical means. Manual egg removal involves  rubbing the eggs off the hut with your fingers  and can mechanically damage eggs, but with the advantage that water quality is not affected. Chemical egg removal employs sodium sulfite to dissolve  the  adhesive that attaches eggs to the hut.  Sodium sulfite  avoids mechanical egg damage but can have the side effect of depriving eggs of oxygen, which may impact embryo survival and larval development and feeding .  To determine which of these methods best supports fish reproductive studies, we tested the e ffects of manual and chemical egg collection on the  percentage  of feeding larvae obtained from spawning pairs of fathead minnows and compared these data to  control  larval numbers obtained when eggs are  naturally  raised to hatching by the male fathead minnow.