New locality for Lepidosiren paradoxa ( Fitzinger , 1837 ) ( Dipnoi : Lepidosirenidae ) in Argentina

This study documents a new locality of the lungfish Lepidosiren paradoxa on the coast of the Entre Rios Province in the lower Paraná River. This finding represents the third southern record of this species on southern of South America. Additionally, as this region has been relatively well sampled both during past decades and currently, I discuss possible reasons why this new specimen has been observed only recently.

was caught by a local fisherman in shallow waters (depth of approximately 3 m) in a coastal area of the locality of General Alvear, Entre Ríos Province, Argentina (31°55ʹ27.60ʺS, 060°39ʹ45.52ʺW) (Fig. 1).After collection, the specimen was frozen and transported to the laboratory for identification.The specimen was identified according to diagnosis of Ringuelet et al. (1967) then deposited in the Fish Collection of the Laboratorio de Vertebrados, Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción (CICyTTP-V-18, Diamante, Entre Ríos, Argentina).The description follows the anatomical nomenclature proposed by Ringuelet et al. (1967).Distribution data for Argentina were taken from Liotta (2006) and Casciotta et al. (2005).Biological and ecological data were taken from Casciotta et al. (2005).
The specimen (Fig. 2) is characterized by an anguilliform (eel-like), elongated, and rounded body, compressed at its caudal end.It measures 950 mm total length.The head is large and fits about 10 times in the total length.ings on either side that are very small.The mouth is terminal, the snout is roun, and teeth are formed by dental plates.The eyes are small.The pectoral and pelvic fins are filiform.The dorsal fin converges with the caudal and anal fins forming a continuous fold; this begins dorsally in the middle of the body and ends in the abdomen at the level of the pelvic fins.The anus is offset from the sagittal plane.The scales are small and embedded in the skin.The color pattern is uniform black.
These animals are especially interesting because of their characteristic body forms, generally large size, and peculiar mode of life.Adult Lepidosiren live as solitary individuals in swamps, or shallow lakes with floating vegetation (Kerr 1950).It is most often found where water has a low conductivity (less than 100 μS/cm) with neutral or slightly acidic pH, and temperatures ranging from 24 to 28°C (Menni 2004).It is a species able to survive drought because it builds a 50 cm deep cavity where it remains buried until conditions improve.During this period, atmospheric oxygen penetrates through the pair of open holes in the top of the shelter, the species' skin secretes a mucus to protect the body, metabolism is reduced, and stored fat in the caudal area is consumed.
Reproduction occurs during the rainy months, when adults move into flooded areas.The eggs are deposited in a nest built in a horizontal cave with a closed bottom that can reach 1.5 m.The males develop filaments known as "pelvic gills" on their pelvic fins and exhibit parental care by protecting eggs and young in the nest (Casciotta et al. 2005).The pelvic gills can be induced to be formed by injections of testosterone (Urist 1973) and are believed to release oxygen into the water of the nest to raise its oxygen levels (Cunningham 1932).External gills are prominent throughout the yolk-sac larval period and are retained in the free-living larval and juvenile stages.These gills are usually resorbed in the seventh week.Juvenile specimens typically have a pattern of bright yellow spots; these spots are lost as the individual grows, with adults achieving a black or slate-grey color (Casciotta et al. 2005).
L. paradoxa has nocturnal habits.It is a predator.It feeds mainly on aquatic invertebrates, like insects, mollusks, and crustaceans that inhabit the bottom of rivers, as well as small fish.Juveniles feed on insect larvae and snails (Casciotta et al. 2005).
This record includes a new locality in Argentina.It is the first confirmed sighting of this species in Entre Ríos Province and the third for the lower Paraná River.Previously, Mac-Donagh (1945) and Giacosa & Liotta (1997) collected other individuals at the Paraná River delta (Table 1).Therefore, the historical records indicate that the presence of L. paradoxa in the delta is sporadic and that the southernmost known locality is San Pedro, in Buenos Aires Province (33°50ʹ S) (Fig. 1).
An interesting observation is that the lungfish which inhabit the Amazonian basin differ from those in the Paraguay basin.For example, occasionally in the Gran Chaco, the habitat dries out almost completely during the dry season.Instead, in Amazonia, the water retreats following seasonal flooding so that the fish can move with the water level from seasonally flooded forests back into permanents channels (Cox Fernandes 1997).An explanation of the finding of L. paradoxa in Entre Ríos province might be the great flood that occurred in 2016 in the Paraná River basin.This kind of event creates connections between different environments through waterlogging.Thus, it is possible that this flood event caused the species to be found several kilometers from its more frequent distribution range.This new record for L. paradoxa only reinforces the need to spend more research effort on different regions of the Paraná River in order to learn about and preserve the fish fauna belonging to one of the world's largest floodplains.
Moreover, L. paradoxa is one of the ornamental fish of the Argentine fluvial coast that are subject of marketing without clear regulations or controls (Gómez et al. 1994).Considering this is a unique lungfish in South America, and is highly vulnerable due to extraction of natural populations without control (although it is not on the list of endangered species), it is important to improve knowledge of this species to inform possible measures of preservation.

Table 1 .
Detail of the records of Lepidosiren paradoxa in Argentina (modified from Liotta 2006).