Your choice of an arapaima fish (Arapaima gigas) to illustrate the alarming decline in giant freshwater fish is misleading (Nature http://doi.org/dbv4; 2019). This species is a conservation success, showing that it is still possible to reverse such megafauna declines.

Arapaima fish are harvested within a legal, sustainable, community-based arrangement pioneered by Brazil’s Mamirauá Sustainable Development Institute in 1999 (www.mamiraua.org.br). Use of this system in the Brazilian Amazon, regulated at the state and federal level, has led to the recovery of wild arapaima populations, with some increasing by more than 425% (J. V. Campos-Silva et al. Freshwater Biol. 64, 1255–1264; 2019).

Although arapaima in the Amazon basin followed the global decline in giant fish populations through the 1990s (F. He et al. Glob. Change Biol. http://doi.org/dbwb; 2019), this was subsequently corrected using management strategies based on stock assessments and government fishing quotas. Such measures have also led to an increase in arapaima populations inside a protected area in the Peruvian Amazon (see go.nature.com/2ndykbg; in Portuguese).