Recombinant luteinizing hormone as a tool towards understanding reproductive dysfunction in captive Macquarie perch Macquaria australasica

The Macquarie perch Macquaria australasica is an endangered freshwater fish endemic to the Murray-Darling Basin in Australia. Captive breeding is considered an essential measure to save the species from extinction, yet its reproductive biology is not fully understood. We produced a recombinant single-chain Macquarie perch luteinizing hormone (rmpLh) in the methylotrophic yeast Pichia pastoris, confirmed by Western blot analysis and mass spectrometry. We developed and validated a heterologous competitive enzyme-linked immunosorbent assay (ELISA) for M. australasica Lh using antibodies generated against the giant grouper Epinephelus lanceolatus Lhb, which is 91% identical to the M. australasica sequence at the amino acid level. Measurement of Lh in plasma samples collected at 2 timepoints (June vs. August 2020) from captive F1 broodstock did not show a significant difference. Plasma Lh in samples from wild fish collected in September 2020, a month prior to the spawning season, were almost 10-fold higher than those of the F1 broodstock. The tools generated here will help us to understand the reproductive biology of M. australasica and develop reliable assisted reproduction techniques for the species.