Collection, Removal, and Quantification of Eggs Produced by Rosy Red Fathead Minnows in Outdoor Pools

Abstract

Eggs produced by rosy red fathead minnows Pimephales promelas held at four densities in 12 outdoor pools were collected and removed from substrate and had their numbers estimated. Adult fish were stocked at a sex ratio of 4:1 (females: males) and at densities of 5.1, 15.3, 25.4, or 35.6 fish/m². Sodium sulfite (1.5–2.0%) was used to detach fathead minnow eggs from the spawning substrate. Egg numbers were estimated volumetrically based on an average (±SD) of 578 ± 34 eggs per milliliter. Mean daily egg numbers generally increased with fish density, and production ranged from 2,587 ± 2,999 to 9,595 ± 2,423 eggs/kg of broodfish. Averaging all treatments together for the 16-d period, over 6,000 eggs/d were collected per kilogram of broodfish. Based on this estimate, 500 kg of broodfish in a 1-ha pond would produce an average of 3 million eggs each day. Assuming an 80% hatching rate, this number of eggs would result in enough fry to stock a 0.5–1.0-ha pond. The results imply that an intensive production method consisting of harvesting eggs from ponds, indoor hatching, and subsequent fry stocking (as is now practiced for other baitfish species) could be feasible for fathead minnows.