Crystal Tetra, Roeboides bouchellei
Crystal Tetra, Roeboides bouchellei. Fish caught from a freshwater stream in Puerto Chomes, Costa Rica, March 2021. Length: 6.5 cm (2.6 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).
The Crystal Tetra, Roeboides bouchellei, is a member of the Tetra or Characidae Family, and is known in Mexico as sardinita cristal. Globally, there are twenty-two species in the genus Roeboides, of which this is the only one found in the freshwater systems of mainland Mexico. The Genus is of scientific interest because they practice lepidophagy, tearing off and ingesting scales from other fishes.
The Crystal Tetra has a strongly compressed head and body that is 30% to 34% of standard length. Their body has the greatest depth at the dorsal fin origin. The lower profile of the head is more inclined and convex; the upper profile is straight. They are a uniform silvery color being dark dorsally with a long extended anal fin that has a yellow margin and a transparent caudal fin. They have a mid-lateral stripe that becomes more prominent towards the caudal fin, is approximately the width of the pupil, and is lighter in color than the body. The key to identification is the presence of a triangular shaped dark spot on their on their caudal peduncle. Their head has a small slightly upturned terminal mouth that is found directly behind the mouth and extends to the center of the large eyes and is equipped with conspicuous teeth on the external margins of the jaws. Their anal fin has 4 spines and 48 rays and originates well before the dorsal fin and graduates downward form the first spine; their caudal fin is deeply forked with pointed tips; their dorsal fin has 2 spines and 9 rays and is followed by a small adipose fin that is midway between the depressed dorsal tip and the caudal base; their pectoral fins are low on the body and reach the anal fin base; and, their pelvic fins are found midway between the anal and pectoral fin origins and extend well beyond the initial anal fin rays. They have 5 to 8 gill rakers. They have 15 to 19 scales above the lateral line and 14 to 20 scales below.
The Crystal Tetra is a benthopelagic schooling species found in all types of freshwater environments in tranquil waters of creeks and shorelines of larger rives with low to moderate current. They are found from sea level in slightly brackish waters to elevations of 610 m (2,000 feet). They reach a maximum of 8.2 cm (3.2 inches) in length. They feed on fish scales of characins and cichlids and aquatic insects. The Crystal Tetra is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Crystal Tetra is found within the freshwater systems of southeast Mexico in the Pacific Slope from Rio Perros at Ixtepec, Oaxaca eastward to Guatemala.
The Crystal Tetra, being the only member of its Genus that is found in Mexico’s freshwater systems is a straightforward identification.
The Crystal Tetra are very abundant in many locations. From a conservation perspective they are currently considered to be of Least Concern, with stable wide-distributed populations. Their long-term viability is threatened by water pollution and habitat degradation caused by human development.