Recirculating aquaculture systems (RAS) can improve the production of farmed abalone, but there are issues with using such systems. An important issue is that the health of shellfish reared in such systems is largely determined by feed type. Therefore, it is important to optimize diets to improve the production of abalone. In this study, Haliotis discus hannai in a recirculating aquaculture system were fed with three types of dry seaweed Saccharina japonica, Undaria pinnatifida, and Pyropia tenera) together with formulated diet (FD) in five different ratios. The different feed treatments were run for 90 days to examine the effects on abalone growth. The highest growth rate was 12.35%, which was observed for shell length in the group fed Pyropia tenera, with 7.01 and 7.14% growth rates in the groups fed Undaria pinnatifida and formulated diet, respectively. A 3.36 % growth rate was observed in the group fed Saccharina japonica alone. However, the addition of appropriate proportions of seaweed to the mixed diet led to better growth, indicating protection against the nutritional deficiencies of FD. The CaCO3 abalone shell mainly comprises aragonite and calcite. Rearing in RAS and natural seawater resulted in 7:3 and 6:4 aragonite to calcite ratios, respectively, with no feed type-based difference. We, therefore, speculate that shell composition is influenced more by the environment than the feed in that the metastable aragonite crystal structure is converted to a stable calcite crystal structure in natural seawater, where minerals are abundant.