Two snapshots of fish diversity and body size in an Amazonian market

Tropical freshwater fisheries support both biodiversity and human livelihoods, yet long-term fishery characteristics data remain scarce across much of the Amazon Basin. Fish markets offer an opportunity to assess patterns in fish diversity and body sizes from exploited aquatic communities. Fish diversity and body sizes (standard length; SL) of common, locally harvested fish sold in Mercado Belén, Iquitos (Peruvian Amazon), were measured using photographic surveys conducted 11 years apart, in 2008 and 2019. Mean SL of the 10 most abundant species or genera differed significantly between these two years for seven taxa, increasing in five taxa (including Prochilodus nigricans and Plagioscion squamosissimus ) and decreasing in two, notably in a large, predatory Cichla sp. Taxonomic richness and diversity showed small declines between these two years. Minor differences in community composition were observed between years, but the dominant taxa were similar. These two time points serve as a baseline for future comparisons and by themselves do not demonstrate temporal or regional trends. Market surveys provide a useful, low-cost complement to field-based ecological studies in tropical freshwater ecosystems.