Rathbun’s tetra in the wild

In the Pantanal wetlands of Brazil, the wet season is the time of plenty. As rivers rise and spill into the surrounding grasslands and forests, fish follow the waters. They move into the newly flooded landscape in search of food, shelter and spawning sites.

Here they may a diverse range of food items, including seeds, fruits, nuts, insects and molluscs. They may even encounter algae, detritus and vegetable matter that provides the boost they need to achieve breeding condition. These aquatic habitats are ripe for exploitation by these fishes.

Newly submersed leaf litter and other decaying matter provides the basis for a new food chain. Tiny invertebrates that feed from these botanicals provide protein to many small fishes. Some of our aquarium favourites such as Hyphessobrycon eques and Hemigrammus ulreyi thrive on these organisms in wild habitats.

Serpae tetra (Hyphessobrycon eques) are common in the fishkeeping hobby.

The temporary underwater world is full of new habitats for the fishes. Including submerged grasses, shrubs, branches, and even entire forest floors. Here, fish can exploit these new environments for cover and safety from predators and as places to breed and raise young.

The flooded meadows over open grassland which sit between fragments of forest are vital nurseries for many fishes. Here I observed a pike cichlid, Crenicichla lepidota, guarding its young as they navigate through the grasses.

Also, tiny juvenile tetras quickly dart into cover when any sudden movement occurs. Apistogramma commbrae also keep a look out while supervising small broods of fry as they forage over the substrate.

One of the most conspicuous species here is the brightly coloured Aphyocharax rathbuni. They are known by a few names in the hobby including the Rathbun’s tetra and the green fire tetra. These fish move through the submerged vegetation grazing on algae which grows soon after the waters arrive.

The rising waters are almost stagnant, with the flow from the river dispersed. This means that the sediment and particles in the water begin to sink and the water becomes clear. This allows lots of sunlight to penetrate the waters.

The power of the tropical sun, beating down through the clear water, is intense. This combined with the vast volume of nutrients entering the water column from the flooded landscape causes an initial boom of algae. The algae covers the leaves of many flooded terrestrial plants, while they slowly adapt to live underwater.

Many plant species in the region can survive months underwater, even if they are not true aquatic plants. Fuelled by the nutrients in the settling sediment, they remain lush until the waters fall once more.

The algae however may burn itself out. So the small Aphyocharax race into newly flooded areas to take advantage of it as quickly as possible. There constant nibbling on the algae may be the clue to their intense green colouration in the wild.

This aquatic habitat is perfect for a biotope aquarium. For more inspiration you can see a video filmed by myself of these fish in their native habitat right here:

 

Words: Tai Strietman

Species which appear in this video:

Salminus brasiliensis

Aphyocharax rathbuni

Hyphessobrycon eques

Characidium laterale

Steindachnerina brevipinna

Cyphocharax gilli

Serrapinnus kriegi

Hemigrammus neptunus

 

Other species encountered in this habitat location:

Hoplias cf. malabaricus

Crenicichla lepidota

Poptella paraguayensis

Moenkhausia bonita

Moenkhausia dichroura

Apistogramma commbrae