Fishing and recording dead fish by citizen scientists contribute valuable data on south American ray-finned fish diversity.

Citizen-collected data are used to describe ecological patterns and to obtain information about the distribution and trends of fauna and flora to inform management and conservation actions worldwide. However, considering the logistical and financial aspects, data should be collected in a cost-effective way. In addition, informed by the spatio-temporal distribution of observations, under-, and oversampled areas can be identified to guide future sampling efforts. Here, we classify 37,161 observations of South American Actinopterygii submitted to iNaturalist, occurring in both coastal and inland water bodies. We consider the status of the fish (live/dead), the characteristics (taxonomy and habitat) of the species and the circumstances of the observation (e.g., during fishing or diving). We test whether adding opportunistic observations increases species diversity, i.e., if observations of dead fish and fishing-related data add information to traditionally collected occurrence data (i.e. those of live fish observed during diving). Our dataset contained 2,377 species of 206 families, representing 24% of all South American ray-finned fish species. Dead individuals and observations related to fishing on average contributed 37% and 33% of annual observed species richness, respectively and added 151 unique species not recorded live or under circumstances not related to fishing. We found that for dead fish the rate of validation by peers and experts on the platform had been 20% lower compared to that of live individuals. We argue that recording organisms observed under different circumstances and in different conditions improves our knowledge of biodiversity. Demonstrating the value of all observations can encourage volunteers to make their data collection more inclusive. [ABSTRACT FROM AUTHOR]