Leptonotus blainvilleanus

Leptonotus blainvilleanus is a fish of the family Syngnathidae, accepted under that name in the World Register of Marine Species ^[1]. Males care for the eggs in an open pouch on the underside, in front of the tail, and the adults measured in Chile were between 129 and 230 mm in standard length ^[2].

It is found among bottom algae in cold coastal waters of the south-eastern Pacific and the south-western Atlantic, with records as far as 46° S in Argentine Patagonia ^[3]. The IUCN Red List assesses it globally as Least Concern ^[4].

Adults studied in Chile had between 18 and 20 grooves on the abdomen and between 48 and 52 on the tail, between 34 and 37 rays in the dorsal fin, between 12 and 14 in the pectoral fin and between 9 and 11 in the caudal fin ^[2]. Standard length of adult males ranged from 129 to 211 mm and that of adult females from 129 to 230 mm ^[2].

The sexes can be told apart in adults. The male carries an open brood pouch on the underside at the start of the tail, about 26 mm long on average, and has no swelling of the abdomen. The female has no pouch, has a deeper body at the abdomen and, when mature, shows small circular spots with a pale centre and a strongly pigmented rim ^[2]. Below about 129 mm in standard length no external feature separates males from females ^[2].

Similar species

• Syngnathus acicularis: It is very similar, but Leptonotus blainvilleanus has a continuous lateral line ^[2].

A Chilean study, citing earlier work, places the species between Hornitos, in Chile, and Golfo Nuevo, in Argentina, and examined specimens caught from 1961 to 1985 between the Gulf of Arauco and Nalcayec Island ^[2].

In August 2010 a male of about 20 cm total length was found in San Jorge Gulf, Argentina, near 46° S, swimming in a tidal channel at less than 3 m depth with the water at 6 °C; a second individual turned up in April 2011 at about 8 m among seaweed meadows ^[3]. The authors note that in the south-western Atlantic it had been reported in coastal waters down to 25 m depth and that, by an estimate they cite, its range reaches at least northern Chile and possibly southern Peru ^[3].

As in other Syngnathidae, parental care is by the male: the eggs lie in a cluster inside the brood pouch, held together by a membrane. In males carrying eggs, the clusters held from 46 to 226 eggs, with an average of 155 ^[2].

Embryonic development was divided into 6 phases. In the last one a dorsal fin and a caudal fin are already visible, which is unusual for fish embryos ^[2]. Newly released larvae measured between 8.7 and 12.8 mm in standard length ^[2].

Males with eggs were found in January, February, September and October; in January, 8 of 9 males carried them. The authors suggest that breeding takes place mainly in spring and summer, but note that mating and incubation periods are unknown because no live material was kept ^[2]. On diet, another report states that it eats small crustaceans and small fish ^[3].

The 66 specimens of the Chilean study were obtained among remains of the alga pelillo, Gracilaria verrucosa, which is harvested from the meadows ^[2]. Other authors describe it as a benthic fish of algal beds in estuaries and coastal areas, hard to see because it is easily mistaken for algae ^[3].

Because all the specimens were caught in Gracilaria verrucosa meadows, the authors of the Chilean study consider it important to take into account the possible effect of harvesting this alga on the species' populations ^[2].

The IUCN assesses Leptonotus blainvilleanus in the global category of Least Concern (LC) ^[4].

A Chilean study, having caught all its specimens in Gracilaria verrucosa meadows, raises the possible effect of harvesting that alga on the species, without quantifying it ^[2].