Bulldog Splitfin

Bulldog Splitfin, Alloophorus robustus

The Bulldog Splitfin, Alloophorus robustus, whose common Spanish name is chegua, is a member of the Splitfin or Goodeidae Family, known collectively as mexclapiques in Mexico. This fish is also known as the Bulldog Goodeid and is the sole global species in the genus Alloophorus.

The Bulldog Splitfins have elongated and narrow bodies with a pointed snout and an elongated caudal peduncle. They are uniform pale brown in color with unspotted fins, a golden area on their gill covers, and a pale area that extends from their throat to their anal fin origin. They have spots on their sides, which vary with maturity; juveniles have numerous large black blotches on their sides which fade with age. They are sexually dimorphic with males being darker than females. Breeding males have black bands mid-fin and terminal yellow bands on their pectoral and pelvic fins. Their head has a short pointed snout, a large terminal mouth with strong jaws and sharp conical teeth, and mid-sized eyes set on the midline. Their anal and dorsal fins are set well back on the body and their caudal fin is lunate.

The Bulldog Splitfins are found in tranquil lakes, ponds, reservoirs and slowly flowing rivers and streams over clay, mud, rock, and sand bottoms at depths up to 7 feet and are often associated with aquatic plants. They reach a maximum length of 17.0 cm (6.7 inches) and are the second largest member of the Splitfin family. They are diurnal carnivores feeding on other fish, insects, and worms. Reproduction is viviparous and involves internal fertilization followed by a short gestation period. Each female gives birth to 20 to 38 live young measuring 1 cm (0.5 inch), which can survive on their own but are subject to cannibalism by their parents.

In Mexican waters the Bulldog Splitfins have historically been found in the freshwater systems within the Mexican Plateau in west-central Mexico, such as the Río Lerma basin and the northwest tributaries of Río Balsas in the states of Guanajuato, Jalisco, and Michoacán. At present, they have disappeared from many of their historical locations and are believed to be widely distributed but uncommon.

The Bulldog Splitfins are used for human consumption but have been overfished. They are also used on a limited basis by the aquarium trade but require high maintenance, large water volumes, frequent water changes, and temperature-controlled environments. They require live food (crayfish, fish, insects, and worms) to breed in captivity. They are also highly aggressive and known to practice cannibalism of their young and predation of their tank mates. From a conservation perspective they are currently considered Endangered. They have disappeared from several known sites and are now found only in a few small and isolated locations. They suffer from a lack of regular monitoring and historical site-specific population data. The water habitat in some parts of their range has experienced a staggering amount of degradation during the 20th century and they are heavily preyed upon by various birds and recently introduced non-native fish including Black Bass, Guppies, Largemouth Bass, Sunfish, and Tilapia.

Bulldog Splitfin, Alloophorus robustus, Female. Fish caught in La Angostura Springs within the Mexican Plateau in west-central Mexico, Michoacán, February 2017. Length: 4.8 cm (1.9 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.

Bulldog Splitfin, Alloophorus robustus, Male. Fish caught in La Luz Springs within the Mexican Plateau in west-central Mexico, Michoacán, February 2017. Length: 10.9 cm (4.3 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.