Recently, aquaculture and captive breeding have commenced for a raft of large fish species, including bluefin tuna (Thunnus orientalis), kingfish (Seriola lalandi) and giant grouper (Epinephelus lanceolatus). With captive breeding, there is often interest to conduct selection and genetic improvement, but these large species present many and substantial challenges to selective breeding. Indeed there are no reports or examples that selection response and forward genetic gain has been achieved for such large and problematic species. These large species, typified by kingfish, are characterized by immense fecundity with ensuing opportunity for intense domestication selection, either adverse or synergistic, that can impact on planned selection response. Moreover, because of size and logistics, typically few broodstock are held and chance sampling of few broodstock individuals has the potential to confound selection response and the repeatability of response.The main objective here was to assess if forward selection response could be achieved after selection for adult weight of kingfish in sea cages. Selection response was estimated by comparing the performance of F1 offspring from wild parents with F2 offspring from selected parents during the larval rearing and adult growout. Pedigree data, from genotyping approximately 1000 individuals using up to 17 DNA microsatellite loci, was added to the larval and adult performance data to resolve the contributions of different sire and dam lineages.For most traits measured, whether larval survival, incidence of larval deformity, adult weights or adult condition factor, the offspring of selected parents outperformed those from wild parents, whether animals were grown separately in replicate (larval rearing tanks) or communally as adults in tanks. Larval survival was not deliberated selected, yet the dropout of specific parental sire or dam lineages suggest in part genetic differences account for some of the differences between the F1 and F2. Observed selection responses for adult weights and condition factor were greater than those predicted from covariances of relatives. Either (synergistic) domestication selection or some type of magnification of line differences under communal rearing may account for these data.The chance sampling of particularly good or bad broodstock sires or dams did not seem to have been a major contributor to the strain testing results. Whether this means that selection responses are repeatable even when using few broodstock, a situation unavoidable for large marine species, is discussed in terms of how intense deliberate and possible domestication selection could narrow the variances of breeding values of selected broodstock. Statement of relevanceCan we select large marine species with few broodstock?