Fish diversity in the Amazon: Freshwater marvels

Brazil, one of the largest countries on the planet, a place we happily call home. Approximately 200 million people live in Brazil, being the most bio diverse  location on the planet and having a massive economic value due to recent marvels in medical discoveries from cancer fighting wasps to frogs, this is also home to the Amazon rainforest, notably called due to the Amazon river cutting through the forest. This river stretches to 6,992km and provides a lot of water to local communities and tribes that need this river and its branching tributaries such as the Rio negro for the fishing economy. This offers sanctuary to a huge variety of organisms which are always under pressure from deforestation, pollution and the exotic pet trade, home to reptiles, birds, mammals, amphibians, plants & fish.

With a estimate made by Reis in 2003, 2,500 species of fish have been described leaving >1000 to be described. However this number continues to raise, with 4,475 species being recognised in 2007 and stated in the book of freshwater fish of south and central America. This number is debated a lot, with the WWF currently having 3000 species being described.

To address this abundance, we must first ask why? What water do these fish favour? Where do they occur? How do biotic and abiotic factors influence the abundance and occurrence of select species of fish?

Following a report written by myself and other colleagues as part of our degree in wildlife conservation & zoo biology, we conducted various biodiversity surveys in the heart of the amazon, for the fish survey we were put into a wildlife reserve, a area of untouched pristine rainforest called Reserva ducke. (Shown below). The city of Manaus is beginning to develop more and more as time goes by and as seen in the image below, it is consuming the forest around the reserve.

Reserva ducke

Reserva ducke


Very few conservation and species monitoring strategies are incorporated into occurrence studies of where fish species occur in the Amazon, however the reserve has a RAPEL grid that is mapped out across the reserve. Using this grid, we set up 50m transects along bodies of water, recording abiotic and biotic variables at interval points on the plots. Light penetration through the canopy, water current, depth, stream width, fish species, sediment type and PH were recorded.

What was noticed was that the water type was very important in species distribution;

  • White
  • Black
  • Clear

Hemmigrammus pretoensis & Laetcara thayeri preferred one plot compared to other fish species we found, this could be due to their morphology as H.pretoensis & L.thayeri share a similar body length of approximately 60mm’s. Using the field guide these species preferred one water type, small streams with changing flow conditions.

This suggests that there is still a lot to learn about the aquatic life, clinging to the murky waters of the most diverse river on the planet earth.




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Josh Brierley

Josh Brierley

Loves wildlife and has a vast hands on experience in wildlife conservation. Currently working with honey bees!

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