Twilight zone (TLZ) hosts the largest and least exploited fish stocks of the world’s oceans. These fishes play a key role in ecosystem services, such as sustaining other relevant marine species and global carbon cycle. The TLZ research is still in its infancy, but the high biomass has raised interest in its exploitation, mainly as fish meal, but also as nutra-pharmaceutical compounds. Moreover, climate change is altering the environmental conditions in ways, of which we do not know how life in TLZ will be affected. It is alarming that this vast ocean domain is at risk even before any of the potential consequences of fishing are fully understood. One of the most threaten and less studied aspects of the TLZ is the early life stage of its fishes. PLEASE project aims to fill this gap of knowledge. The first objective is to set background information about basic biology of the embryonic and larval development of different TLZ fishes. It will be achieved by establishing a suitable methodology for assisted reproductive technology in laboratory conditions, since the wild TLZ fishes are vulnerable to captivity. The reproductive methodology will be transferred to the non-academic partner, for developing pioneered aquarium exhibitions. The second objective is to examine the developmental responses of the embryos and larvae due to ocean warming and acidification under climate change scenarios. It will be monitored via the developmental variability, metabolism, physiology, morphometry, and mortality rates of the specimens. The outcomes of the project will be of paramount importance to forecast the impact of climate change on the community of TLZ fishes and will open a new era for more investigation in this pristine and vulnerable zone of the planet. Finally, a range of interactions with stakeholders and public will ensure the project exploitation and improve the decision-making capacity of the policymakers related with climate change and fishing activities in the TLZ.