Mass selection based on mass spawning can present a feasible and low-cost selective breeding scheme. In mass spawning, however, mating is not controlled and a small number of breeding individuals may account for a lafgeproportion of the next geperation, leading to higher inbreeding, decrease in performance of stocks and no response to selection: To understand the mating systems, reproductive and population parameters under mass spawning, we conducted mass spawnings with female to male sex ratios of 1:1,2:1 and 3:1. We analysed parentage, established the effective number of parents contributing to the next generation and calculated reprodtlctive parameters and the associated level of inbreeding in an experimental breeding unit. Considering the breeding units as basic building blocks, mass selection breeding programmes based on mass spawning can be implemented by extrapolating the number of breeding units depending on the size of the nucleus and the intensity of selection. Such schemes require minimum investments in infrastructure and can be adopted as a model for low-cost and effective selective breeding schemes that will produce the desired response without compromising the long-term fitness of culture populations due to inbreeding.