Assessing the sustainability of mass selection for increased fecundity in five generations of selectively breeding of Acartia tonsa Dana, 1849 (Calanoida: Copepoda)

Copepods are highly valued live feed organisms for aquaculture hatcheries worldwide, but availability is scarce. In Norway, a domesticated line of Acartia tonsa is cultivated commercially, but it has never been selectively bred to improve phenotypic traits. In this study we designed a semi-controlled breeding system to select for improved egg production in female copepods and bred them for 5 generations. Egg production increased substantially in the first three generations, with a net improvement of ~67% more eggs female −1 day −1 , but no subsequent improvements were observed in the final two generations. Genomic analyses indicate that the selected population is significantly distinct from its commercial source but incurred only minor inbreeding accumulation ( F ST = 0.024) and lacks evidence of extreme changes in allele frequencies at individual genetic markers. Mass selection for improving relevant production traits in A. tonsa appears to have strong potential, but the strategies to generate long-term genetic gains remain uncertain. • Selective breeding in the copepod Acartia tonsa generated a 67% improvement in egg production over three generations. • Egg production did not continue to improve in generations four and five, for unknown reasons. • Genetic differentiation of the selected line was distinct, but inbreeding was minor. • Mass selection appeared favorable: loss of genetic diversity was offset by increased breeding population size.