Intra-sexual competition plays an important role in the evolutionary process of sexualselection. Male-male competition over resources that are essential for mating success mayprevent unsuccessful competitors from breeding. The intensity of competition is influencedby the availability, quality, and distribution of such resources. The spatial distribution ofresources may facilitate monopolisation, limit the density of breeders and skew thereproductive success among individuals in a population. In some species, one such resourceis favourable nests sites, which males compete for, occupy and defend against intruders. Theaim of this study was to test the extent to which nest spacing, and specifically inter-nestdistance, induces intra-sexual competition (territorial aggression). In order to address thisquestion I focused on how distance between pairs of nests affects nest occupancy, matingsuccess and asynchrony in breeding of male two-spotted gobies (Pomatoschistus flavescens),a small fish with a resource defence based breeding system and uniparental care provided bymales. Results show that shorter inter-nest distance did not affect nest occupancy, matingsuccess or asynchrony in breeding of males and does not appear to intensify male-malecompetition. These results suggest that nest spacing does not limit the density of breedingmales. However, further studies are required to understand the effect of nest spacing on theintensity of sexual selection. The high occupancy rates, irrespective of distance, suggest thatthe artificial nests are favourable nesting sites. Although potential natural nesting sites for thetwo-spotted gobies seem to be abundant in the studied area, high-quality nests might be inlimited supply.