Yellowtail Kingfish cultured in net pens can experience growth cessation and even weight loss during the winter period when temperatures fall below optimum. As an emerging, group spawning species, knowledge of genetic improvement strategies in this species is limited. Genetic improvement for winter resilience present an opportunity to improve productivity with shorter production cycles and increased eFCRs. This requires repeated individual weight measurements across a production cycle, which is impractical to evaluate on large net pens. Post winter condition index was evaluated across two generations of a yellowtail kingfish breeding programme representing six year classes. A moderate heritability of 0.28 was observed with an increase of post-winter condition index Breeding Values from 14.26 (±0.03) to 14.43 (±0.04) across generations. Genetic correlations of 0.47 are also shown between post-winter condition index and tank-based fasting daily growth coefficients (DGCs) corroborating supporting that post-winter assessment will enable selection for improved ability to maintain weight through winter. These results demonstrate the potential of selectively breeding for winter performance in yellowtail kingfish. In addition, it is one of the first examples of realized genetic gains from selective breeding in this species.