Corvina drum

Cilus gilberti is a fish of the drum family (Sciaenidae) native to the southeastern Pacific, with records in Peru and Chile ^[1]. It lives over soft bottoms in the coastal zone and is a resource for artisanal fisheries ^[2]. It eats small crustaceans and fishes such as anchoveta, and as of 2000 little was known of its basic biology ^[2]. The IUCN lists it as Data Deficient (DD) ^[3].

The species was described as Sciaena gilberti in 1899 and is now accepted in the genus Cilus; Cilus montti, described in 1900, is a synonym ^[4].

Until 1985 it was treated as two different species ^[5]: juveniles were known as corvinilla (Sciaena gilberti) and adults as corvina (Cilus montti) ^[2].

Among 827 specimens measured off Talcahuano, Chile, total length ranged from 25 to 106 cm and weight from 299 g to 17 kg ^[2]. Another source gives a maximum length of 92 cm and has no recorded size at maturity ^[1].

It is endemic to the southeastern Pacific. In Chilean waters it is recorded in the north at Arica (18°20'S) and in the south at Chiloé (43°06'S), associated with soft bottoms of the coastal zone over the continental shelf ^[2]. FishBase places it in Peru and Chile, between latitudes 6°S and 37°S ^[1].

It is a neritic fish of sandy or muddy bottoms ^[5]. In southern Peru, in 2016, specimens were caught in a rocky and sandy zone on the beaches of Punta Colorada and Punta Mesa, near Sama (Tacna), 50 m from the low-tide line ^[6].

Of the 827 specimens analysed off Talcahuano between August 1994 and July 1995, 56.6 % were female, 35.2 % male and 8.2 % could not be sexed because the gonad was still incipient; almost all fish under 35 cm were immature or of undetermined sex ^[2]. FishBase has no recorded size at maturity ^[1].

In captivity, 21 wild fish caught in 2016 in Tacna all survived (100 %) through the 7 months of conditioning, in water of 15.3 to 19.7 °C and with dissolved oxygen of 5.65 to 8.09 mg/l ^[6]. They fasted for 23 to 31 days before starting to eat; they first accepted fresh crustaceans (Emerita analoga) and frozen anchoveta and bonito, and later a formulated feed ^[6].

Although at least 24 prey types turned up in the stomachs, the diet is concentrated on a few: by the index of relative importance, anchoveta Engraulis ringens and mysids each contributed about 49 % of the total ^[2]. Fish under 36 cm ate mostly crustaceans, whereas in fish over 60 cm fishes weighed as much as crustaceans ^[2]. In winter the main crustacean became the euphausiid Euphausia mucronata, at 52 % of the index ^[2].

In 86 corvinas studied off Talcahuano in 1983 and 1998, 26 taxa of metazoan parasites were recorded, and every host was parasitised ^[5].

Its global IUCN Red List category is Data Deficient (DD), according to the 2020 assessment ^[3]. In Chile it was already noted in 2000 that there was almost no information on basic aspects of its biology despite fishery interest ^[2].

The authors of a 2019 Peruvian study report that corvina populations have declined and that the El Niño phenomenon affects them ^[6]. FishBase estimates its vulnerability to fishing at 51 out of 100 ^[1].

It is an important resource for artisanal fisheries in Chile, whose catches go to human consumption ^[2]. FishBase rates it a highly regarded table fish in South America and a commercial fishery species ^[1].

The swim bladder of drums is sought to make colapez ^[6]. In Tacna, the Morro Sama Aquaculture Centre (FONDEPES) caught wild corvinas in 2016 to build a broodstock, the basis of a first captive culture ^[6].

The only Peruvian study consulted for this account documents catches on the Sama coast (Tacna), between Punta Colorada and Punta Mesa, over three outings in 2016, 50 m from the low-tide line ^[6]. That study describes no diving observations ^[6].

The 21 fish of that study were taken to the Morro Sama Aquaculture Centre, a FONDEPES facility ^[6].