"To that end, Hermann and three co-authors published a study today (June 8, 2016) in the new online journal, Royal Society Open Science, that reports on the use of chemical analysis of ear-stones or "otoliths" as a way to tease out a fish's life story, potentially revealing its migratory routes and the environments it encountered in its travels. The paper, titled "Unravelling the life history of Amazonian fishes through otolith microchemistry," describes the identification of chemical markers that can trace a fish back to the Amazon estuary and to "black water" vs. "white water" rivers. Another marker reveals that at least one species, the Amazonian corvina, may not be as sedentary as previously believed, raising new questions about how best to ensure the long-term survival of this economically important fish.

The study is part of an emerging body of knowledge that lays critical groundwork for the conservation and management of these threatened species. The goal is to provide fisheries managers and conservationists with better information about how to protect fishes from threats that include deforestation, mining, oil drilling, construction of dams for hydroelectric power, and overfishing."

Theodore W. Hermann, Donald J. Stewart, Karin E. Limburg, Leandro Castello
Published 8 June 2016.
DOI: 10.1098/rsos.160206\

Abstract

Amazonian fishes employ diverse migratory strategies, but the details of these behaviours remain poorly studied despite numerous environmental threats and heavy commercial exploitation of many species. Otolith microchemistry offers a practical, cost-effective means of studying fish life history in such a system. This study employed a multi-method, multi-elemental approach to elucidate the migrations of five Amazonian fishes: two ‘sedentary’ species (Arapaima sp. and Plagioscion squamosissimus), one ‘floodplain migrant’ (Prochilodus nigricans) and two long-distance migratory catfishes (Brachyplatystoma rousseauxii and B. filamentosum). The Sr : Ca and Zn : Ca patterns in Arapaima were consistent with its previously observed sedentary life history, whereas Sr : Ca and Mn : Ca indicated that Plagioscion may migrate among multiple, chemically distinct environments during different life-history stages. Mn : Ca was found to be potentially useful as a marker for identifying Prochilodus's transition from its nursery habitats into black water. Sr : Ca and Ba : Ca suggested that B. rousseauxii resided in the Amazon estuary for the first 1.5–2 years of life, shown by the simultaneous increase/decrease of otolith Sr : Ca/Ba : Ca, respectively. Our results further suggested that B. filamentosum did not enter the estuary during its life history. These results introduce what should be a productive line of research desperately needed to better understand the migrations of these unique and imperilled fishes.