Hoplosternum Littorale - Ecology

Ecology

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 (sub)tropical 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. The respiratory intestine is well-developed between days 24 and 32.

H. littorale has two types of hemoglobin, anodic and cathodic; anodic hemoglobin has a relatively low oxygen affinity and has marked Bohr effects, while cathodic hemoglobin lack significant pH effects. In H. littorale, cathodic hemoglobin has a pronounced reversed Bohr effect in which oxygen affinity increases with decreased pH. Cathodic hemoglobin has the purpose of safeguarding oxygen transport to tissues under hypoxic and acidotic conditions.

H. littorale diet varies by age. Immature fish feed primarily on small aquatic crustaceans, especially Cladocera, Ostracoda, Copepoda, and Eubranchipoda. Chironomid larvae are important items in the diets of both juveniles and adults. The adult diet is dominated by mixed detritus, terrestrial insects, microcrustaceans, and aquatic beetles during the dry season, and mixed detritus and chironomid larvae during the wet season.