It is often assumed that in reproduction bigger body size is favourable. Large female are known to produce more higher-quality eggs and the survival of their juveniles is better than among small females. However, even though also larger male body size is likely to affect reproductive success at least through mate choice, competition and nest guarding, this has rarely been studied experimentally. The study by Uusi-Heikkilä et al. investigates the role of both male and female body size in zebrafish and, surprisingly, detects that among the largest males the reproductive success is reduced compared to average-sized males. The possible explanation is that these male are so dominant towards females that the females get stressed and the reproduction suffers. The findings of the study has also drewn attention in the largest Finnish newspaper Helsingin Sanomat (in Finnish only).
Uusi-Heikkilä S., A. Kuparinen, C. Wolter, T. Meinelt, R. Arlinghaus. Paternal body size affects reproductive success in zebrafish (Danio rerio). Environmental Biology of Fishes doi:10.1007/s10641-011-9937-5