To obtain a large amount of biologically active fish gonadotropins (GtHs), recombinant red seabream GtHs were produced using a baculovirus expression system. Using a dual vector expression strategy, heterodimeric GtHs were successfully produced in silkworm larvae. These recombinant GtHs had the same bioactivity as purified GtHs, regarding the stimulation of in vitro steroid hormone production.