If you want to learn more about how the charismatic creatures known as stingrays feed, you should check out a new study published in the most recent issue of Neotropical Ichthyology.

While spending days and nights scuba diving and snorkelling in the upper Paraná River of Brazil, researchers Domingos Garrone-Neto and Ivan Sazima made 132 observations of freshwater stingrays and noticed three different forms of foraging behaviour.

Picture of Motoro Sting Ray, Ocellate river stingray – Potamotrygon motoro.
Copyright www.jjphoto.dk

The first hunting technique involved hovering close to the bottom, or even settle on top of it, while undulating the disc margins. By doing so, the stingray would stir up the substrate, unveiling small invertebrates. The invertebrates – typically snails, crabs and larval insects – could not escape from under the ray’s disc and ended up as food.

When using its second hunting technique, the stingray would slowly approach shallow water while keeping its eyes on suitable prey items that concentrate in such environments. When it got close enough, it would make a rapid attack; stunning the prey or trapping it under its disc. This hunting technique did not target tiny invertebrates hiding in the sand; it focused on tetras and freshwater shrimps instead. The studied stingrays only used this method during the night when they could sneak up on prey without being seen.

The third technique observed relied on the presence of vertical or inclined surfaces in the water, such as boulders and tree stumps, including man-made structures like concrete slabs. On this type of objects a lot of different organisms, e.g. snails, like to crawl around or attach themselves. The hunter would simply position itself with the anterior part of its disc above the water’s edge and start picking the animals off the surface, one at a time.

The two studied species were Potamotrygon falkneri and Potamotrygon motoro; both belonging to a genus of freshwater stingrays found exclusively in South America.

As mentioned above, you can find the paper in Neotropical Ichthyology 7.

Garrone-Neto, D and I Sazima (2009) Stirring, charging, and picking:

hunting tactics of potamotrygonid rays in the upper Paraná River. Neotropical Ichthyology 7, pp. 113–116.

The cichlid genus Crenicichla now has two new described members: Crenicichla tesay and Crenicichla mandelburgeri.

Crenicichla tesay

Crenicichla tesay lives in the Paraná River drainage and was described by Argentinian ichthyologists Jorge Casciotta and Adriana Almirón. The fish was caught in the Iguazú River upstream of Iguazú falls in Argentina, an environment characterized by falls and pools with clear and rapidly flowing water. The bottom in this habitat consists of stones, mud and sand.

The name Crenicichla tesay is derived from the Guaraní word for tears; the fish displays a tear-shaped suborbital stripe. You can distinguish Crenicichla tesay from its close relatives by the existence of a serrated posterior preopercle border, the number of scales on the E1 row, the length of the snout, and the colour pattern which consists of a suborbital stripe, 4–6 dark blotches and numerous irregularly scattered dots on the sides of the body.

The description has been published in the journal Revue Suisse de Zoologie[1]. For more information, see the paper: Casciotta, J and A Almirón (2008) Crenicichla tesay, a new species of cichlid (Perciformes: Labroidei) from the río Iguazú basin in Argentina. Revue Suisse de Zoologie 115, pp. 651–660.

Crenicichla mandelburgeri

Just like Crenicichla tesay, this newly described cichlid hails from the Paraná River drainage. It was described by Swedish ichthyologist Sven Kullander and named Crenicichla mandelburgeri in honour of Paraguayan ichthyologist Darío Mandelburger.

The Crenicichla mandelburgeri specimens were collected from two different environments. Some lived in the rapids of a large stream (5-10 meters wide and up to 1 meter deep) with turbid, brownish water. Others lived in a much smaller stream (up to 3 meters wide) with shallower brown water where both velocity and transparency fluctuated. In this environment, the bottom consisted of stones and sand and was generally without any plants.

Young Crenicichla mandelburgeri cichlids feature numerous narrow vertical bars along the side, which changes into an irregular dark horizontal band as the fish matures. You can also distinguish Crenicichla mandelburgeri from other crenicichlas by the distinct caudal blotch, the number of scales in the lateral row and in the E1 row, the lower jaw (which is longer than the upper), and the serrated preopercular margin.

For more information, see the paper: Kullander, SO (2009) Crenicichla mandelburgeri, a new species of cichlid fish (Teleostei: Cichlidae) from the Paraná river drainage in Paraguay. You can find it in Zootaxa 2006: 41–50.[2]

Crenicichla

Crenicichla is the cichlid genus where you can find the largest number of described species, about 75 species. They live on the South American continent where they inhabit freshwater rivers, streams, pools and lakes. The richest variation of species is encountered in the Amazon region, but you can find Crenicichla cichlids as far north as Guyana, Venezuela and Colombia and as far south as Uruguay and central Argentina where the water can become fairly cold in the winter.