Defensive capability of egg-guarding males of the goby,tridentiger kuroiwae brevispinis

The capability of egg-guarding maleTridentiger kuroiwae brevispinis to defend their own nests and egg masses, measured experimentally by matching them with conspecific male competitors of various body size, was almost total against competitors of body lengths ≦104% of defending male body length. Against competitors with body lengths >116% of defending male body length, nest and egg defence almost always failed, indicating an upper limit of competitor's relative body size (between 104% and 116%) against which successful nest and egg-guarding is possible. The specific growth rate of egg-guarding males was significantly lower than that of non-egg-guarding males, due to starvation and stress. The results suggested that male body size has a major influence on guarding males' reproductive success, through post-spawning male-male competition.