Demographic structure is critical for a fish population to maintain its spatial distribution pattern. Overfishing, however, is likely to increase the aggregation potential of fish populations through altering their demographic structure (i.e. size truncation). b value of Taylor’s power law (V=a*M^b) is an effective index of the aggregation potential; a higher b indicates a higher potential for a population to aggregate when its abundance increases. While the aggregation potential of a population has been found to be correlated with the life history traits across species, no research has investigated if such relationship exists within a population. Here, we examined the within-population relationship between b values and body size for eight fish species, using the IBTS data spanning 25 years. Our results showed a hump-shaped relationship between Taylor’s exponents and body size with the peak around the mature length, suggesting the critical role of the large individuals in maintaining a more homogeneous distribution when the population abundance increases. More importantly, our results gave a mechanistic explanation of how size truncation raises spatial heterogeneity and aggregation potential of a population, highlighting the importance of maintaining a sound size and spatial structure for adult fishes in management.