Pundamilia nyererei is a species of freshwater fish in the Cichlidae family. It is found in lakes in Kenya and Tanzania. It is becoming rare due to habitat loss.
In may not be a great surprise to learn that fish are the most species-rich vertebrate group on the Planet–with an estimated 32,500 member species. But what is surprising is that 43% of these species are found in freshwater habitats, such as lakes and rivers.
This rich diversity of freshwater species is all the more startling when one considers that freshwater systems represent just one hundredth of one percent (.01%) of the Earth’s surface water. According to Fishes of the World (J.S. Nelson), over 5000 new species of freshwater fish have been discovered in just the past three decades–a time period marked by expanded exploration of fish habitats and better understanding of “taxonomic boundaries” (mostly, due to more accurate genetic analysis).
One might suppose that many of these newly discovered fish–many quite rare–are endangered, but in fact, only a small fraction of these “newer” fish have contributed to the increase in overall threatened species (H.L. Jelks et al, Fisheries 33). While rarity is often correlated with extinction risk, some rare and ancient species (like the powan and pollan fish of the British Isles) have survived since the end of the last Ice Age. Invasive species, habitat fragmentation or loss (from both human and natural causes), and even reckless collecting are the leading causes of imperiled freshwater fish worldwide.
According to the same 2008 study noted above (Jelks et al), nearly 40% of freshwater species in North America are either at risk of disappearing or have already vanished. Representing some 761 distinct species, 230 are deemed “vulnerable”, 190 are threatened, 280 are endangered, and 61 are extinct (or extinct in the wild). These numbers represent a 90+% increase over a 1989 assessment of freshwater species. And these trends are consistent with assessments in Europe.
Making matters worse are increasing demands for water resources and on-going or predicted impacts from climate change. Ecologists and biologists have long suggested remedies: restoring habitat, implementing better resource management practices, limiting harvests of vulnerable species, restricting transport of threatened fish, and controlling pollution. This latter remedy is often the most difficult to effect. Land run-off (from farm land or home waste water) and other effluent often promote eutrophication (an over-supply of metabolic nutrients, like phosphates) which can inhibit same-species recognition, which can lead to interbreeding. This blurring of specie boundaries makes it more difficult to track individual species, and thus to implement specific conservation strategies (see: Seehausen, van Alphen, and Witte).
But what makes freshwater fish conservation so challenging is the fact that freshwater fish diversity is a function of freshwater fish rarity. Often, rare species–like the Picote de Tequila (Zoogoneticus tequila), a live-bearing fish found only in a small, 4 meter wide pool in Ameca Basin in Central Mexico–are found in isolated locales, or scattered , small lakes or ponds. In many cases, a quite small population of breeding adults supports the entire species population. In the case of the Picote fish, the entire population of 500 is preserved by just 50 adults.
Still, these rare and small populations manage to hang on. It has been suggested that the evolution of freshwater fish has been safe-guarded because of their rarity. Their small numbers and isolated habitats have nurtured unique adaptations–like sperm storage in guppies–that manage to secure the species long-term survival. Additionally, isolation means less exposure to competition (from other species) and predation, as well as pathogens. It is also thought that many such freshwater fish are so well-adapted to their local habitats that their genomes have fewer, disadvantageous mutations. In this regard, strategies to repopulate rare, freshwater fish species in situ using their zoo-bred relatives are being seriously discussed. It is not known how the native species would be affected by this strategy–whether added genetic diversity would promote its survival, or whether the introduction of genes selected for under domestic (zoo) conditions would actually weaken the species, and hence its odds of survival.
Primary reference material for this article: Threats to Freshwater Fish, by Anne E. Magurran, Science Magazine, 4 September, 2009.
Fish Drawing: Robbie Cada
About Michael Ricciardi
