Peacock Bass Science and Conservation – Peacock Bass pH Tolerance

Peacock Bass Environments

Peacock Bass In Acidic Amazon Waters

By Paul Reiss

Blackwater Environment

The more anglers know about their quarry, the better they are able to successfully pursue it and manage its conservation. The giant peacock bass (Cichla temensis) roams a blackwater environment that is so significantly different from that of temperate zone freshwater sportfish, that it is worthwhile for peacock bass anglers visiting the Amazon to gain an understanding of the peacock’s home waters. The following article attempts to provide some insights via a research project assessing fishes’ acid tolerance in blackwater environments Throughout North America, Europe and Asia, pollution has caused serious damage to aquatic ecosystems. One of the worst culprits is acid rain. Resulting mostly from sulfur emitted by power plant smokestacks, this toxic acidification has been shown to cause massive fish kills and a serious loss of biodiversity in our lakes, rivers and streams.

On the other hand, in the Amazon basin, highly acidic “blackwater” regions exist that support a huge diversity of fishes in spite of being far more acidic than even our most damaged waters. In fact, this is the preferred home of the giant peacock bass. The most powerful freshwater gamefish in the world, lives in water with enough acid content to kill most species! The obvious question you might ask is, “How is this possible?” Many researchers have asked the same question. The answer may lie in the tea-colored material that gives blackwater its name.

Blackwater is formed when wet, oxygen-poor soils permit the slow decay of matter from vascular plant material. Runoff delivers a constant supply of this mixture of dissolved organic matter (mostly made up of tannic and humic acids). Not only does this material deliver blackwater’s characteristic coloration, but scientists have found convincing evidence that it actually protects fishes against the poisonous effects of acidic environments.

Acid water causes fishes to lose their body salts. Freshwater species have a biological pumping system in the cells of their gills that keeps the salt in their bodies from leaking out into the salt-free freshwater that surrounds them. Acid conditions attack these cells and cause them to stop working. The material in blackwater, however, appears to provide a protective effect for these cells, enabling them to continue to work normally. The peacock’s own ecosystem may be what protects it from environmental toxicity that kills fish elsewhere.

The Amazon is a giant enigma, with thousands of interlocking puzzles waiting to be solved. We haven’t even begun to understand how they fit together. Here is just one more reason why it must be protected at all costs. With more study, we might learn how to use Amazon-based knowledge to protect fishes in each of our various backyards. Perhaps we’ll find that reducing the constant deforestation in our countryside might put more of these blackwater materials into our waters and help slow the rate of environmental degradation and fish loss.

Note – The following unpublished paper is the result of an experiment performed on non-Amazon fishes, with an eye toward understanding more about the nature of Amazon Blackwater systems. The reference materials cited in this paper can provide additional information regarding this subject matter from peer-reviewed sources.

Laboratory Analysis of the Effects of Blackwater on Low pH Tolerance in Fishes

PAUL REISS; Rutgers University, Graduate Program in Ecology and Evolution, New Brunswick, NJ, 08901, USA
Rutgers University Marine Field Station, Tuckerton, NJ

Abstract

The unusually high level of fish biodiversity found in acidic “blackwater” systems in the Amazon basin suggests that the humic and fulvic acids in blackwater may provide some form of protection against the toxic effects of low pH, or that fishes endemic to this environment may be more tolerant of those effects. These ideas were tested by two experiments in a laboratory study. In the first experiment, seven fish species from three water types were subjected to a treatment regime of reduced pH to compare the species’ tolerance to pH toxicity. Species examined included: Enneacanthus obesus, Micropterus salmoides and Aphredoderus sayanus from blackwater; Fundulus heteroclitus, Menidia menidia and Cyprinodon variegatus from brackish water and Lepomis macrochirus from clear freshwater. The results demonstrated markedly different resistance to mortality in low pH among the species, as measured by the cumulative concentration of excess H+ ion over time. For example, Enneacanthus was able to tolerate almost three times as much exposure as Lepomis, a member of the same family, and over eight times the exposure of Cyprinodon, a brackish water fish. The results also demonstrated that fishes from blackwater are more resistant to low pH toxicity, as a group, than fishes from other source waters.

In a second experiment, the effect of water type on tolerance to low pH was measured among a subset of species selected from the first experiment, i.e., Fundulus heteroclitus, Cyprinodon variegatus and Lepomis macrochirus. Resistance to mortality ranged from 20% to 100% greater in both blackwater and brackish water than in clear freshwater for each species. These results indicate that there are effects inherent in both blackwater and brackish water that protect fishes against low pH and which are lacking in clear freshwater. The study examines the physiological aspects of pH toxicity in various water types, considers differences in innate or acquired tolerance to low pH among species and analyzes the relevance of ecosystem management strategies in relation to the toxic effects of acidification.

To read the full report, please click here.

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