For many fish populations reproductive patterns remain unknown, which often results in inadequate management strategies. Timing and intraspecific variability in the main reproductive traits of ballan wrasse (Labrus bergylta) were investigated based on microscopic analysis of gonads sampled from NW Spain in 2009–2012. This species displays two main body colour patterns, plain and spotted, which coexist in sympatry. Females spawned from January to April whereas spawning capable males were present almost year-round. Length at 50% maturity did not differ between colour patterns and was above the minimum catch size. Plain individuals attained the length and age at 50% sex change earlier than spotted individuals, which might be explained by differences in growth patterns, mortality rates or by an evolutionary genetic divergence between populations. Individuals with gonads infected by encysted trematode metacercariae were associated with an earlier timing of sex change, which represents one of the few examples of a possible parasitic influence on the sex allocation of its host. Our findings provide a framework for scientific-based management of this hermaphrodite fish.