What primary requirement made keeping wild-caught Yellow Tangs difficult in early captive settings?

They required the continuous supply of natural marine algae that early aquariums could not provide.

A significant hurdle in the early history of keeping Yellow Tangs in captivity related directly to their strict dietary needs derived from their highly specialized herbivorous niche in the wild. Because their survival depended on constant grazing of algae off rocks and corals, providing adequate nutrition in early home aquariums proved extremely challenging. Most early systems lacked the capacity to continually supply the necessary volume and variety of natural marine algae. This dietary deficiency, combined with stress, resulted in high mortality rates among wild-caught specimens until aquaculture research could successfully address this maintenance challenge by developing prepared foods they could eventually accept.