Anisotremus scapularis

Anisotremus scapularis is a marine fish of the family Haemulidae, described by Tschudi in 1846 ^[1]. It is known in Peru as «chita» ^[2], and in Tacna also as «sargo» ^[3]. It is commercially important in the country, where it is among the species prioritised for aquaculture development ^[4]. On the IUCN Red List it is assessed as Least Concern ^[5].

It ranges from Ecuador to Chile ^[6]. It is a carnivorous species that lives on the bottom and in the water just above it, that is, a benthopelagic fish ^[2].

On the coast of Callao, 81 wild females caught between January 2019 and December 2020 were studied: they spawn asynchronously, with indeterminate fecundity, and their mean length at first maturity, computed as L100, was 25.3 cm ^[4]. The gonadosomatic index was highest in summer, and the authors place the spawning season between late spring and mid-autumn ^[4].

The eggs, obtained from natural spawning in the laboratory, measure on average 0.752 mm across and carry an oil globule of 0.165 mm ^[6]. At 19 °C the larvae hatch between 31 and 41 hours after fertilisation and measure about 2.558 mm at hatching ^[6].

In southern Peru, a group of broodfish caught at sea began spawning on their own 7 months after capture, and there embryonic development took 42 hours at 18 °C ^[7]. In Tacna, fish caught by hook and line off the beaches of Llostay spawned for the first time in captivity on 29 October 2016, with the water at 18 °C ^[3].

For juveniles, the optimum temperature was estimated at 18.7 ± 2 °C, and above 32.6 °C or below 10.1 °C death is immediate ^[8].

It copes poorly with low oxygen: in juveniles, half of the individuals died within 36 minutes with the water at 60 % saturation, whereas Paralabrax humeralis showed no mortality after 31 days at 5 % ^[9]. Faced with hypoxia, this grunt tends to avoid it rather than lower its activity, so the authors regard it as especially vulnerable to such events ^[9].

It hosts a varied parasite fauna: in 20 fish bought in Lima in 2013, 10 helminth species were identified, including monogeneans, trematodes, acanthocephalans and nematodes ^[2].

Its global category is Least Concern ^[5]. Even so, its fishery on the Peruvian-Chilean coast is described as small and irregular, and as a textbook case of illegal, unreported and unregulated fishing ^[10]; other authors describe its population as overexploited ^[7].

Its fishery also affects other species: this grunt is among the target species most associated with the incidental capture of Humboldt penguins in Peru and Chile ^[11].

It is one of the most valued fish in Peru's markets ^[10]. Methods already exist for catching, transporting and conditioning wild broodfish for farming, and in the south of the country they have produced spawnings year after year since September 2016 ^[7]. An economic analysis concluded that raising it in recirculating systems on the Peruvian-Chilean desert coast would be profitable with a 15-month cycle and a price of 6.67 dollars per kilo ^[10].