Predicted impacts of climate warming on aerobic performance and upper thermal tolerance of six tropical freshwater fishes spanning three continents.

Dominique Lapointe,Steven J Cooke,Lee Hannah,John S Balirwa,Michael S Cooperman,Marcio S Ferreira,Matthew Mwanja,Limhong Chhom,Timothy D Clark,Anthony P Farrell,Adalberto L Val,Lauren J Chapman,Dismas Mbabazi,Les Kaufman

doi:10.1093/conphys/coy056

Abstract

Equatorial fishes, and the critically important fisheries based on them, are thought to be at-risk from climate warming because the fishes have evolved in a relatively aseasonal environment and possess narrow thermal tolerance windows that are close to upper thermal limits. We assessed survival, growth, aerobic performance and critical thermal maxima (CTmax) following acute and 21 d exposures to temperatures up to 4°C higher than current maxima for six species of freshwater fishes indigenous to tropical countries and of importance for human consumption. All six species showed 1.3–1.7°C increases in CTmax with a 4°C rise in acclimation temperature, values which match up well with fishes from other climatic regions, and five species had survival >87% at all temperatures over the treatment period. Specific growth rates varied among and within each species in response to temperature treatments. For all species, the response of resting metabolic rate (RMR) was consistently more dynamic than for maximum metabolic rate, but in general both acute temperature exposure and thermal acclimation had only modest effects on aerobic scope (AS). However, RMR increased after warm acclimation in 5 of 6 species, suggesting incomplete metabolic compensation. Taken in total, our results show that each species had some ability to perform at temperatures up to 4°C above current maxima, yet also displayed certain areas of concern for their long-term welfare. We therefore suggest caution against the overly broad generalization that all tropical freshwater fish species will face severe challenges from warming temperatures in the coming decades and that future vulnerability assessments should integrate multiple performance metrics as opposed to relying on a single response metric. Given the societal significance of inland fisheries in many parts of the tropics, our results clearly demonstrate the need for more species-specific studies of adaptive capacity to climate change-related challenges.

Highlights

Inland fisheries can be critical to the food security of developing nations in tropical regions (Béné et al, 2015; Youn et al, 2014)
specific growth rate (SGR) did not differ between the temperature treatments for the other three species (Brycon amazonicus, L. victorianus, Barbonymus gonionotus; Table 2)
We present our results as evaluations of the applicability of two hypotheses: that equatorial fishes will lack capacity for adaptation and will be severely challenged by warming water temperatures (CVH), and that a decline in aerobic scope (AS) will be the causal mechanism of the whole-animal performance decline (OCLTT)

Summary

Introduction

Inland fisheries can be critical to the food security of developing nations in tropical regions (Béné et al, 2015; Youn et al, 2014). Inland fisheries can be central to national and regional poverty alleviation strategies of many tropical countries by providing a primary source of income via sale of fish, a means for barter, stable full time and seasonal employment, and commercial development opportunities with associated taxable revenue (Béné et al, 2009; Neiland and Béné, 2006; Nunan, 2013). Inland fisheries of the tropics typically occur in locations of high taxonomic diversity and involve indiscriminate harvest of all available species and sizes (Kolding and van Zwieten, 2014; McIntyre et al, 2016; Welcomme et al, 2010). The status and conduct of tropical inland fisheries is directly associated with efforts to protect global biological diversity

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