Pacific moonfish

Selene peruviana is a fish of the family Carangidae, with a very deep, compressed body, that lives in coastal waters of the eastern Pacific ^[1],[2]. It is known from California to Peru and forms schools close to the bottom ^[2]. It feeds mostly on fishes of the family Engraulidae and on small crustaceans ^[3]. In northern Peru it is, according to a source the authors cite, among the 7 fishes caught most often by the artisanal fishery, although its commercial value is low ^[4]. Its global IUCN Red List category is Least Concern ^[5].

Guichenot described it in 1866 as Vomer peruvianus, in a publication of the Linnean Society of Maine-et-Loire (France); the current name joins the genus Selene to the original epithet ^[1]. Selene comes from the Greek word for the moon ^[2]. Another scientific name, Vomer declivifrons (Meek and Hildebrand, 1925), is now an unaccepted synonym ^[1].

In English it is called Pacific moonfish or Peruvian moonfish ^[1],[2].

The body is very short, deep and compressed ^[2]. The dorsal fin has 8 separate spines, followed by 1 more spine and 21 to 24 soft rays, and the lower part of the first gill arch carries 30 to 35 gill rakers ^[2]. In adults the front lobes of the second dorsal fin and of the anal fin are not elongated, whereas in juveniles the front dorsal spines are drawn out ^[2]. The modified scales of the lateral line (scutes) are very weak and poorly differentiated ^[2].

Adults are silver or golden with a bluish metallic sheen, while the juveniles are silver and carry a dark oval blotch over the straight section of the lateral line ^[2]. The largest recorded size is 40 cm total length, and a common size is 24 cm fork length ^[2]. In Ecuador, the mean total length of landed fish was 23.62 cm in males and 22.97 cm in females ^[6]; in Tumbes, the mean of 80 fish was 24.56 cm ^[4].

In the eastern Pacific the genus has 3 species: Selene peruviana, Selene brevoortii and Selene orstedii ^[4]. The sources we read do not compare their features, so this account offers no key for telling them apart ^[4].

It is an eastern Pacific species: FishBase gives its range from Redondo Beach, in southern California, to Peru, and treats it as rare north of Baja California; its records lie between about 34° N and 18° S ^[2]. García-Alcalde and colleagues place it from the Gulf of California to the coast of Peru, and occasionally in northern Chile ^[4].

It is benthopelagic: adults live in coastal waters, usually in schools near the bottom, and juveniles are found near the surface; FishBase gives a depth range of 0 to 50 m ^[2]. García-Alcalde and colleagues describe it on sandy bottoms of the coasts of the Americas, and juveniles are spread from the surface down to 50 m ^[4]. A source cited in an Ecuadorian study places it on the continental shelf between 10 and 80 m ^[6].

Reproduction was studied in 886 fish landed in Ecuador between January 2017 and December 2018 ^[6]. The size at maturity, measured as the total length at which half of the fish are mature, was 22.61 cm in males, 23.86 cm in females and 23.27 cm for both sexes together ^[6]. The gonadosomatic index reached its highest values in February and March, the period of greatest reproductive activity, and the sex ratio was 0.70 males per female ^[6].

In northern Peru, García-Alcalde and colleagues indicate, without naming a source, that peak spawning falls between March and May, and their sampling, from June to October 2018, lay outside that period ^[4]. They used 21.5 cm as the length at first maturity, a value they take from Tripp-Valdez and colleagues ^[4]; but those authors explain that the size and age at first maturity of Selene peruviana are not known and that 21.5 cm is the value for another species, Selene setapinnis, of the eastern Atlantic ^[3].

The length-weight relationship has an exponent of 2.63 (r² = 0.89), which indicates negative allometric growth: the fish gains weight somewhat more slowly than it grows in length ^[6]. Because the size at maturity is close to the mean size of the catch, the authors suggest that the species may be at the limit of its optimal catch size ^[6].

In the southern Gulf of California, off Nayarit and southern Sinaloa, 114 stomachs containing food (of 208 examined), from fish of 8.5 to 26.5 cm fork length, showed that engraulids were the most important prey: they occurred in 51.75 % of the stomachs and made up 89.55 % of the weight of the food ^[3]. Shrimps of the family Ogyrididae were the most numerous prey, at 35.93 % of individuals, and there were also crustacean remains, shrimps of the genus Processa and euphausiids ^[3]. The trophic position was 3.72 from the stomachs and 3.9 from stable isotopes, and the Levins niche-breadth index was 0.17, which the authors read as that of a specialist or opportunistic predator ^[3].

Parasites were studied in 80 fish caught between June and October 2018 at Puerto Zorritos, Tumbes: 66 of them (82.50 %) carried at least one species ^[4]. A total of 326 parasites of 7 species were counted, among monogeneans, one trematode and copepods, and the monogenean Oaxacotyle oaxacensis was the most frequent, with a prevalence of 56.25 % ^[4]. All are new records for the species and for Peru ^[4].

The IUCN Red List classifies Selene peruviana globally as Least Concern, according to the 2008 assessment ^[5]. FishBase rates its vulnerability to fishing as low to moderate (28 out of 100) and its resilience as high ^[2].

In Ecuador, the bycatch of the sardine purse-seine fleet fell from 5,402.8 t in 2004 to 2,680.49 t in 2019 ^[6]. The authors of that study suggest that, because the size at maturity resembles the mean size of the catch, the species may be near the limit of its optimal catch size ^[6].

It has little commercial value and in some countries is sold as a third-class fish ^[4],[3]. Even so, in the artisanal fishery of Tumbes it is among the 7 fishes caught and marketed most often, according to the literature reviewed by García-Alcalde and colleagues ^[4]. FishBase describes it as a minor fishery, sold fresh, salted or dried ^[2].

In Ecuador it is an important resource for artisanal and industrial fishing, and the authors of that study say its meat is well valued in the market; it is taken with purse seines, trawls and gillnets ^[6]. In Mexico it often appears as bycatch of the shrimp trawl fishery ^[3].

The Peruvian literature available describes the species on sandy bottoms of the coasts of the Americas, without naming sites in Peru ^[4]. The 80 fish of the most recent parasitological study were collected at Puerto Zorritos, Tumbes (3°40' S), between June and October 2018 ^[4]. We found no source saying where it can be seen underwater in Peru, so this account recommends no site ^[4].