Mechanical properties of the venomous spines of Pterois volitans and morphology among lionfish species

Abstract

The red lionfish, Pterois volitans, an invasive species, has 18 venomous spines: 13 dorsal, three anal and one on each pelvic fin. Fish spines can have several purposes, such as defense, intimidation and anchoring into crevices. Instead of being hollow, lionfish spines have a tri-lobed cross-sectional shape with grooves that deliver the venom, tapering towards the tip. We aimed to quantify the impacts of shape (second moment of area) and tapering on the mechanical properties of the spine. We performed two-point bending at several positions along the spines of P. volitans to determine mechanical properties (Young's modulus, elastic energy storage and flexural stiffness). The short and recurved anal and pelvic spines are stiffer and resist bending more effectively than the long dorsal spines. In addition, mechanical properties differ along the length of the spines, most likely because they are tapered. We hypothesize that the highly bendable dorsal spines are used for intimidation, making the fish look larger. The stiffer and energy-absorbing anal and pelvic spines are smaller and less numerous, but they may be used for protection as they are located near important internal structures such as the swim bladder. Lastly, spine second moment of area varies across the Pterois genus. These data suggest there may be morphological and mechanical trade-offs among defense, protection and intimidation for lionfish spines. Overall, the red lionfish venomous spine shape and mechanics may offer protection and intimidate potential predators, significantly contributing to their invasion success. present I as a hydrated spine property for goals 1 and 2 above. In addition, we treated flexural stiffness (EI) as a hydrated spine property when we multiplied hydrated Young's modulus (E) with dehydrated second moment of area (I ). RESULTSMorphology and mechanical properties of P. volitans 6

Dermal modifications of the red lionfish, Pterois volitans

“…In these four specimens, the superior and inferior spines are recurved, and similar to the length and shape of the pelvic and anal spines (Galloway & Porter, 2019;Halstead, Chitwood, & Modglin, 1955; Figure 6c,d). The superior and inferior caudal spines are tightly connected to the fin by soft connective tissue and appear to be modified fin rays (Figure 6c,d), and are separate structures from the original 12 caudal fin rays of this species.…”

Genome Sequencing of the Japanese Eel (Anguilla japonica) for Comparative Genomic Studies on tbx4 and a tbx4 Gene Cluster in Teleost Fishes

“…Chinese yellow catfish ( Pelteobagrus fulvidraco ) secretes venom through its fin spines, which has been proposed by us to be essential for the development of marine drugs [36]. Eeltail catfish (Siluriformes), scorpionfish and stonefish (Scorpaeniformes) also have venomous fin spines that can severely injure other animals [37]. As we determined in the present study, an inversion of the brip1-tbx4-tbx2b-bcas3 cluster occurred in these Acanthopterygii fishes (Figure 7), which are in line with the existence of fin spines.…”

Lionfish envenomation in Caribbean and Atlantic waters: Climate change and invasive species

“…Lionfish are members of the scorpionfish family (Scorpaenidae), known for several types of venomous fish, such as the stonefish, whose venom can be lethal to humans. The lionfish subfamily, Pteroinae, has five genera of ornately colored predatory fish, whose distinctive dorsal and pectoral fins are armed with spines that can administer an exquisitely painful venom ( Galloway and Porter, 2019 , Mouchbahani-Constance et al, 2018 ).…”

“…The lionfish retracts the spine’s epidermal covering, and the merest brush of the spine against human skin will induce an immediate searing pain. The pain is caused heat-labile peptide neurotoxins that have mostly sensory effects (pain) and relatively mild neuromuscular effects ( Galloway and Porter, 2019 , Mouchbahani-Constance et al, 2018 ). The pain resolves naturally over several days, but its resolution can be hastened by immersing the affected region, most commonly a hand or finger, in hot water (nonscalding, approximately 40–45 °C) for 30 to 90 minutes to denature the toxin ( Atkinson et al, 2006 , Diaz, 2015 , Perkins and Morgan, 2004 ).…”

“…4 Two dorsal spines with epidermal sheaths retracted manually. The spines are not hollow; thus, they do not deliver the venom in a needle-like fashion, but instead, the venom is exuded by glands at the base of the spine and travels distally along the spine’s outer grooves ( Galloway and Porter, 2019 ). …”