Astyanax cocibolca is a small Central American freshwater fish found primarily in Lake Nicaragua.

This is thought to be because the scales of type species Astyanax argentatus were large and silvery in a way that could be compared to armor or a shield.

[8] Astyanax cocibolca is a small and slender-bodied fish, reaching a maximum of 5.4 cm (2.1 in) SL (standard length, excluding the tail fin).

[6] Fins in some mixture of red, orange, yellow, and clear are common features in members of Astyanax.

[11] This places it primarily in southern Nicaragua, ranging into the relevant Atlantic drainages of northern Costa Rica.

[4] It was formerly considered one of very few fish species endemic to the direct Lake Nicaragua ecosystem,[12] but has since had range extensions into the Sarapiqui and Tortuguero drainages.

Inshore inhabitants will eat primarily fruits, seeds, and algae, and this is not unusual; A. aeneus has a similarly fruit-heavy diet.

[2] Lake Nicaragua itself is relatively shallow and low-elevation, with substrate largely composed of grayish mud and organic silt.

[1] Its type locality, Lake Nicaragua, is under ecological pressure from factors including cattle farming that leads to erosion, pesticide usage, and wastewater inflow from coastal towns; local government agencies are strongly considering an ecotourism program to prevent such factors from worsening conditions further.

[16] These factors make Lake Nicaragua the focus of several different conservation efforts at once, which provides something of an ecological buffer for species such as A. cocibolca.