Importance of Nest and Paternal Characteristics for Hatching Success in Fathead Minnow

We quantified the importance of nest and paternal characteristics for survival of eggs of Fathead Minnow, a multiple-batch spawner in which breeding males guard and tend nests. We stocked experimental ponds three weeks apart and then intensively monitored 150 nests. Nest predation by conspecifics accounted for most of the egg mortality, and 29% of all nests failed to produce hatchlings. Although egg survival was not affected by date of stocking or nest Initiation, hatching success improved In larger and longer-lasting nests. Nests where paternal care was observed during our monitoring were larger, lasted longer, and thus were more likely to produce hatchlings than nests where care-giving was not observed. Over one-third of the male caregivers displayed agonistic behaviors toward nest intruders, and this index of aggressive defense was also associated with improved nest performance. Larger males nested earlier and were more likely to be aggressive than smaller males. Post-spawning mortality of these larger, early-nesting males may facilitate a mid-summer demographic shift among breeders over the spawning season: nests of large, aggressive males are followed by those of smaller or later-maturing fish, who are more likely to survive to spawn again the following year.