Introduction to OPFish by Jean Noel Druon: Productive fronts that result from the resurgence of subsurface nutrient-rich waters such as on the edge of eddies or gyres were shown to attract fish and top predators (Druon et al. 2017, 2016, 2015, 2012, Panigada et al. 2017) as they are active long enough (from weeks to months) to allow the development of mesozooplankton populations (Druon et al. 2019). These productive oceanic features, which are daily detected by ocean colour satellite sensors, are used as a spatial proxy of food availability to fish populations. The satellite-derived Ocean Productivity index for Fish (OPFish) represents the potential production of high tropic level communities (fish) which results of the analysis of feeding preferences of various trophic levels such as mesozooplankton, small pelagic fish, hake recruits, tuna species, fin whale and blue shark. Typical integration time of chlorophyll-a front occurrence (at 4.5 km horizontal resolution) is of few days for the changing pelagic environment and related predators while it is of about six to eighteen months for the more static demersal species and communities. This analysis of habitat at different trophic levels and the linked generic index of productivity useful for fish show how productive fronts are common hotspots of productivity for the marine food chains. We are currently comparing this index to spatial data from commercial fisheries at different resolution (from 0.5 to 0.05 degree) and to scientific surveys in the North-East Atlantic and in the Mediterranean Sea. The OPFish index monitors the capacity of the oceans to sustain living resources under the current effect of climate change but independently of fisheries. The interaction between spatial fishing effort and OPFish, which is a proxy for potential fish distribution, will help guiding the distribution of effort to avoid overfishing and facilitate sustainability.