Fish die-off in river and reservoir: A review on anoxia and gas supersaturation

Angelo Antonio Agostinho,Diego Correa Alves,Fernando Mayer Pelicice,Miguel Petrere Jr,Rosa Maria Dias,Luiz Carlos Gomes

doi:10.1590/1982-0224-2021-0037

Angelo Antonio Agostinho, Diego Correa Alves + Show 4 more

Open Access

https://doi.org/10.1590/1982-0224-2021-0037

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Abstract

Abstract Albeit massive fish mortality has an extraordinary visual impact and is certainly a fatality, we still have rudimentary understanding on how addressing this problem in the Neotropical region. The processes that lead to fish die-off events are complex and sometimes ephemeral, which can lead to incorrect diagnosis. In this review, we discuss these events in Neotropical freshwaters, both in areas impacted by dams and natural environment, with a focus on deaths mediated by the lack of oxygen (anoxia) or the excess of dissolved gases (gas supersaturation). We examine the available knowledge about the related mechanisms, lethal thresholds for dissolved oxygen (DO) and total dissolved gases (TDG) for fish, and the sequelae of gas bubble disease (GBD). An assessment of the main mortality events in Brazil in the last 10 years is also presented, as well as the best practices for monitoring, prevention, and mitigation. Finally, it is concluded that the proliferation of hydroelectric plants in the Neotropical region might contribute to the expansion of these events and, consequently, increasing of impacts on fish conservation. We consider urgent the inclusion of this topic in the licensing processes for new hydropower projects by the environmental agencies.

Highlights

Massive mortality of fish are common events in hydroelectric plants, but their relevance as impacting fish conservation varies widely (Agostinho et al, 2007)
The success of prevention measures depends on understanding how fish interact with dams and reservoirs, which is complicated by the existence of many variables and multiple interactions
To organize existing data and generate information relevant to the management of dams in South America, we provide an overview of fish mortality and injuries in hydroelectric dams with special emphasis on the roles played by oxygen concentration (DO) and total dissolved gas supersaturation (TDGS)

Summary

Human impacts on fish diversity

Embora mortandades massivas de peixes tenham impacto visual extraordinário e sejam certamente uma fatalidade, estamos ainda engatinhando no entendimento e na solução desse problema. Os processos que levam aos eventos de mortes de peixes são complexos e algumas vezes efêmeros, o que explica diagnoses incorretas. Nessa revisão nós discutimos esses eventos em bacias hidrográficas neotropicais, tanto em barragens como em ambientes naturais, porém com o foco nas mortes por falta de oxigênio (anoxia) ou excesso de gases dissolvidos (supersaturação gasosa). Em particular são examinados o conhecimento disponível acerca dos processos que levam a essas condições, os limiares letais de oxigênio dissolvido (OD) e gases totais dissolvidos (GTD) para os peixes e as sequelas da doença das bolhas de gás (DBG). Uma avaliação dos principais eventos de mortandade que ocorreram no Brasil nos últimos 10 anos é também apresentada, bem como discutidas as melhores práticas para o monitoramento, prevenção e mitigação.

INTRODUCTION

Findings

Frequency of death events n