Brown Hoplo

H. littorale is armor-plated and dorso-ventrally compressed. The fish will grow in length up to 24.0 centimetres (9.4 in) TL. Males grow to a larger average and maximum size than females and, during the reproductive season, develop fat deposits in the pectoral fin and an elongated recurved pectoral spine that often assumes a reddish colour. Males with recurved pectoral spines are not found outside of the reproductive period.

H. littorale has the widest distribution of any callichthyid. It is present in all of South America east of the Andes and north of Buenos Aires, including the Orinoco, Trinidad, coastal rivers of the Guianas, Amazon River drainage, Paraguay, lower Paraná River, and coastal systems in southern Brazil. It ranges from Venezuela and Guyanas to Argentina. One single lot is known from the upper Paraná River and the São Francisco River drainage; it has been suggested that these occurrences may represent introduced populations. This species has also been introduced into the Indian River Lagoon of Florida.

Most activity of non-breeding H. littorale such as feeding and locomotor activity are mainly nocturnal. It has a maximum reported age of 4 years. The diet of H. littorale consists mainly of benthic invertebrates and detritus. H. littorale natively inhabits tropical standing waters or swamps. It is not found in rainforest creeks and clearwater rivers draining Precambrian Guyana and Brazilian Shields, where water is extremely poor in dissolved minerals. This species is restricted to swamps of tropical and subtropical South America and the floodplains of Amazonian whitewater rivers originating in the Andes. Such environments are characterized by low levels of dissolved oxygen and markedly seasonal conditions caused primarily by fluctuations in rainfall. H. littorale can breathe both with gills and through its intestines. However, intestinal respiration is not exhibited upon hatching, and the development of the respiratory intestine occurs throughout the juvenile period (up to 32 days old). Newly hatched larvae do not have the ability to breathe air through their intestines; however, it is possible that they absorb oxygen through their skin at this point, before the armor plates have developed. Soon after, between about 12–23 days of age, young have the capacity to breathe air, but their respiratory intestine has not finished developing. …