Stone scorpionfish

Scorpaena mystes is a scorpionfish of the family Scorpaenidae, described by Jordan and Starks in 1895 ^[1]. In Peru it is known as «pez diablo» and «diablo chalaco» ^[2]. It goes unnoticed by keeping still on shallow rocky bottoms ^[3], and its fin spines carry venom glands that can cause painful wounds ^[4]. The IUCN Red List assesses it as Least Concern ^[5].

The name Scorpaena plumieri mystes, which treated it as a subspecies of Scorpaena plumieri, is now listed as a synonym, as is Holoscorpaena didymogramma Fowler, 1944 ^[1]. The two species are closely related even though they live in different oceans: Scorpaena plumieri in the western Atlantic and the Caribbean, and Scorpaena mystes in the eastern Pacific ^[6].

In a sample of 233 fish from the Gulf of California, females measured 19.0 to 44.5 cm in total length and males 15.3 to 35.5 cm; on average females were longer and heavier than males, and a maximum size of 51 cm has been reported for the species ^[4]. In the field, males and females cannot be told apart by eye ^[3].

It lives in the eastern Pacific, from California in the United States to northern Chile, the Galapagos Islands included, on bottoms from 0 to 30 m deep ^[7]. It is a bottom fish of shallow water that uses algae-covered reefs as well as open sandy ground, and it has been recorded down to 85 m ^[4].

In Peru it appears in the historical fauna reports for the Lobos de Afuera Islands under the name Scorpaena plumieri mystes ^[8].

Its age was read from the otoliths of 233 fish speared off Santa Rosalía, Baja California Sur, between May 2015 and April 2016: it lays down one ring a year, and the males were 2 to 10 years old while the females were 3 to 15 ^[4]. Females grow more slowly but reach a larger average maximum size, with an estimated asymptotic length of 48.22 cm against 34.76 cm in males, and the length to weight relation points to isometric growth ^[4].

In the same area, histology of the gonads of 258 fish showed a short breeding season, from May to August, and only in July were males and females ready to spawn at the same time, after the sea surface temperature had risen from 22.9 °C in May to 29.0 °C in July ^[3]. Size at first maturity was estimated at 26.2 cm in total length for females, 27.5 cm for males and 27.2 cm for the population as a whole, and from the ovary slides the authors consider it likely that each female releases her eggs all at once or over a brief period ^[3].

It hunts without moving: it stays completely motionless on shallow rocky bottoms, like a stone, both to catch its prey and to stay hidden from its predators ^[3]. It is regarded as an opportunistic predator that eats mostly crustaceans and small fish ^[4].

Its skin is also a surface for other organisms to settle on: the community growing on fish from the eastern coast of Baja California Sur held 30 diatoms unknown from Mexican shores, and 12 of them had never been recorded on American coasts before ^[9].

Its global category on the IUCN Red List is Least Concern ^[5].

In Mexico its commercial fishery is recent, there is no management plan for the species and the state of its stocks is unknown; based on its reproductive biology, a minimum catch size of 27.2 cm in total length and a closed season from May to August have been proposed ^[3].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

Its fin spines have venom glands that can cause painful wounds and serious breathing problems ^[4]. Its venom contained proteins resembling the alpha and beta subunits of the cytolysin of Scorpaena plumieri and other likely pore-forming toxins; it also broke down proteins and hyaluronic acid, burst and clumped red blood cells, and made nerve membranes leaky ^[6].

At Santa Rosalía, cadmium, copper and lead were measured in adult fish caught between May 2015 and April 2016: cadmium stayed below the detection limit and the hazard index for copper and lead was under 1 for every age group, so the authors conclude that eating it poses no risk to the population ^[10].

In the Gulf of California it was long a minor species for artisanal fishers because of its venomous spines, but since 2012 falling catches of Lutjanus peru and Seriola lalandi have pushed up its price and the volume landed, and its flesh is now valued as excellent ^[4].

In Peruvian literature, the historical reports for the Lobos de Afuera Islands, off northern Peru, list it as Scorpaena plumieri mystes, although neither the baseline studies nor the environmental DNA sampling of November 2018 detected it ^[8]. These islands are a marine protected area within the Guano Islands, Isles and Capes National Reserve, lie some 32 nautical miles offshore, and the distance and their complex seabed limit access ^[8].