By Julien Staub
Before starting into the scientific examination of how to differentiate the 4 most common genera in the Scorpaenidae family, I would like to briefly talk about my personal motivation for writing this article. Coming from a non-biological environment back home, my time at Gili Shark has been amazingly educational and I have immensely enjoyed being around so many like-minded people with such passion for and knowledge of the local marine fauna and flora. For the first time in my life, I felt surrounded by people who shared my fascination and with whom I could talk about such topics.
Among all the beautiful wildlife in Gili, my personal favourites were the fish or invertebrates that manage to hide in plain sight, make them seemingly impossible to spot. After the sense of elation of having spotted one during the dive subsided, I was often left with a nagging feeling of uncertainty of what exactly I had seen. Consulting a fairly comprehensive book of fish species at Gili Shark, usually with the generous help of the knowledgeable people around, then proved to be my place of resolution.
However, this cycle of elation, confusion, help and insight kept continually repeating itself, which culminated in me (finally) sitting down and doing the henceforth following research for and writing of this blog, with the added benefit of my lovely dive buddies receiving better-informed hand signals from this point forward.
This article will focus on distinguishing the four genera of the Scorpaenidae family most commonly found within the Gili Matra MPA (marine protected area):
- Lionfish (Pterois)
- Scorpionfish (Scorpaena)
- Devil Scorpionfish (Scorpaenopsis diabolus)
- Stonefish (Synanceia)
To start off, we will first take a look at the similarities all these genera share, before then diving into the differences and how to best identify them whilst diving.
The Scorpaenidae family comprises over 1’400 species distributed globally across tropical and temperate marine environments (D’Iglio et al., 2024). Members of this family predominantly exhibit solitary, benthic (bottom-dwelling) lifestyles, often displaying morphology and pigmentation that closely mimic their substrates (Poss, 1999). They function primarily as ambush predators, characterized by generally sedentary behaviour, remaining in similar locations over extended durations and can even be observed using their pelvic fins to move along the substrate rather than swim (Lamar University, n.d.). Camouflage is facilitated by coloration mostly within the red to reddish-brown spectrum, consistent with their benthic habits (Poss, 1999). Morphologically, Scorpaenidae typically possess a rounded caudal fin, a pronounced suborbital ridge, and a dorsal continuous fin bearing a series of spines extending posteriorly from the back (Poss, 1999).
With these commonalities established, we will delve into the differences between the genera. Given the often species-specific descriptions in scientific literature, I have taken academic descriptions of individual species and generalized the most prominent descriptions to match the characteristics of the genera that have helped me identify them while diving.
Lionfish (Pterois)
Lionfish are readily distinguished by their elongate, fan-shaped pectoral fins and aposematic (warning) coloration (Chou et al., 2023). Unlike other Scorpaenidae, lionfish exhibit more active predatory behaviour, actively pursuing prey albeit at a measured pace (Peterson & McHenry, 2022).
Scorpionfish (Scorpaena)
In personal experience, of the three remaining species, scorpionfish can most easily be identified by their slender, elongated head, similar to that of a lionfish. They possess deep concavities between eyes and mouth, with the snout-like mouth being on the same horizontal level as the eyes, called oblique in scientific terms (Randall, 2002). Additionally, to better camouflage the outline of their body, scorpionfish can have fleshy protuberances resembling algae around their snouts (Fogarolo, 2021).
Stonefish (Synanceia)
Stonefish diverge morphologically through a robust, less streamlined body, exhibiting a flattened, ‘pancake-like’ profile (Poss & Eschmeyer, 2003). Their mouths are positioned beneath the eyes, characterized by an upturned shape that imparts a distinctive ‘grumpy’ facial expression (Poss & Eschmeyer, 2003; Fogarolo, 2021).
Devil Scorpionfish (Scorpaenopsis diabolus)
The devil scorpionfish, colloquially referred to as the false stonefish, exhibits morphological traits intermediate to scorpion- and stonefish. Notably, a conspicuous hump formed by branching post-temporal spines posterior to the head imparts a distinctive humpbacked silhouette (McGrouther, 2021).
Sources:
Chou, T., Liu, M. & Liao, T. (2023). Systematics of lionfishes (Scorpaenidae : Pteroini) using molecular and morphological data. Frontiers in Marine Science 10:1109655.
D’Iglio, C. et al. (2024). Ecomorphological adaptation of Scorpaena porcus (Linnaeus, 1758): evidence from two different environments revealed by sagittae features and somatic growth rates. Frontiers in Marine Science 11:1347897.
Fogarolo, C. (2021). How to differentiate stonefish from its more common cousins: the Bearded Scorpionfish and Devil Scorpionfish. The Smiling Seahorse. https://www.thesmilingseahorse.com/blog/scorpion-fish-identification-stonefish-vs-devil-vs-scorpionfish.
Lamar University. (n.d.). Spotted Scorpionfish. Lamar University. https://www.lamar.edu/arts-sciences/biology/study-abroad-belize/marine-critters/marine-critters-1/spotted-scorpionfish.
McGrouther, M. (2021). False Stonefish, Scorpaenopsis diabolus (Cuvier, 1829). Australian Museum. https://australian.museum/learn/animals/fishes/false-stonefish-scorpaenopsis-diabolus.
Peterson, A. & McHenry, M. (2022). The persistent-predation strategy of the red lionfish (Pterois volitans). Proceedings of the Royal Society B 289, 1980.
Poss, S.G. (1999). Scorpaenidae. Scorpionfishes (also lionfishes, rockfishes, stingfishes, stonefishes, and waspfishes). p. 2291-2352. In Carpenter, K.E. & Niem, V.H. (eds.). FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Vol. 4: Bony fishes part 2 (Mugilidae to Carangidae). FAO.
Poss, S.G. & Eschmeyer, W. (2003). Scorpaenidae. Scorpionfishes (also rosefishes, rockfishes, stingfishes). p. 1232-1265. In Carpenter, K.E. & Niem, V.H. (eds.). FAO species identification guide for fishery purposes. The living marine resources of the Western Central Atlantic. Vol. 2: Bony fishes part 1 (Acipenseridae to Grammatidae). FAO.
Randall, J. (2002). Revision of the Indo-Pacific scorpionfish genus Scorpaenopsis, with descriptions of eight new species. Indo-Pac. Fishes, 34 pls-1.
