1. Ecological Distribution P. volitans is a tropical marine species, usually found along the forereef in its native Indo-Pacific region. They spend their days hiding in rocky outcrops or caves, and emerge at night for feeding (Fishelson 1975, 637). In their native region, they are near-shore fish but in their invasive region og the western Atlantic and Caribbean they are found further off shore (Kimball et al. 2004, 270). Kimball et al. determined in a laboratory that the chronic lethal minimum temperature for lionfish is about 10° C, and the fish stop eating at around 15° C (273).
Although these limits are likely to vary in the wild, they are useful initial estimates. Based on these estimates, Morris (2009) predicts that P. volitans could eventually reach the coast of Brazil (13). In their native range, the water temperature can drop from 26-27° C in the summer to 19-20° C in the winter (Fishelson 1997, 401), suggesting that lionfish need some method of dealing with the changing temperatures. Fishelson (1997) demonstrated in a lab setting that P. volitans was able to survive a three-month starvation and only lose 9-19% of their body weight through finding a safe place to hide and rest until food became available.
Because they are poikilothermic, they are able to lower their metabolism to handle lower temperatures, as well as food shortages (401). There is little evidence of predation or parasites on lionfish, although instances do exist (Morris 2009, p. 24 & 126). Lionfish have venomous spines that are used as a defensive measure against predators. Morris (2009) demonstrated in an experiment with black sea bass that the bass exhibited avoidance behavior towards the lionfish, and the lionfish didn’t try to flee when the sea bass was within striking distance (124).
This could suggest that the lionfish does not have many natural predators to restrict their distribution. The lack of predation on lionfish in the Western Atlantic may even be a contributing factor to their spread throughout the Caribbean. II. Behavior P. volitans is a nocturnal species. They emerge from their hiding places at sunset when the daytime fishes are making their way to their evening resting places. This interchange period is the time of the highest biodiversity on a reef, and so it affords predators optimal hunting conditions (Fishelson 1975, 638-639).
The lionfish move with slow undulating motions of the caudal fin and the rear portion of their anal and dorsal fins (Fishelson 1975, 639). When hunting, the lionfish use their large, wing-like pectoral fins to hide the motion of their caudal fins so that they can sneak up on prey. Another useful feature for sneaking through the reef, especially at night, is the “cryptic striped pattern of the head and fins,” (Fishelson 1975, 639). When the lionfish is within striking distance of its prey, it sucks the prey in with its large mouth.
Any water that is sucked in with the prey is forced out through the opercular slits, while the prey is kept inside the mouth by the dense gill rakers (Fishelson 1975, 640). P. volitans has an additional hunting method. They sit motionless just below the surface of the water, waiting for fish who are trying to get away from some other predator. If the fish jumps out of the water, they sometimes land right in front of the lionfish, allowing the latter to catch a meal with minimal effort (Fishelson 1975, 640). When they hunt for invertebrates, the lionfish glide over the sea-floor, vibrating the ends of their fin rays.
The escaping invertebrates are then snatched up by the lionfish. P. volitans is primarily piscivorous, but will also eat shrimp (Fishelson 1975, 641). Lionfish are, however, selective in their feeding habits. Fishelson (1997) demonstrated in a lab setting that juvenile lionfish are able to learn relatively quickly that it is dangerous to eat anemone fish, such as Amphiprion bicinctus, because they may get stung when the potential prey swims into the anemone for cover (399). The lionfish will continue feeding until total darkness, but if the moon is specially bright, they may prolong feeding into the later hours of the night (Fishelson 1975, 642). P. volitans is usually a solitary animal, only congregating during spawning events, but every once in a while individuals will bump into one another during feeding. The lionfish will react antagonistically towards the intruder. They will turn their dorsal fins towards one another, and their coloration will darken as a threatening sign. P. volitans will sometimes chase the invader away from its territory (Fishelson 1975, 642).
Similarly, male lionfish will react aggressively when another male interferes with its mating ritual. The initial male will spread his fins wide and approach the intruding fish. He darkens in coloration, while the intruder pales and lowers the anterior portion of the body towards the ground. After this, the initial male will move back and forth in front of the intruder, pointing his dorsal spines at the intruder. If the intruder still has not fled, the initial male will facing the intruder with his pectoral fins spread out and undulating and his dorsal fins strongly erect.
Next, the initial male will move his head back and forth close to the intruding male in order to make himself occur bigger. Finally, if nothing else scared away the intruder, the initial male will try to bite the intruder’s head, and shake him vigorously (Fishelson 1975, 643-645). Females tend not to display similarly aggressive behavior towards one another. Courtship in P. volitans begins shortly before total darkness (Fishelson 1975, 649). The male always initiates, looking for females who are ready to spawn (Fishelson 1975, 646).
While there is usually no sexual dimorphism in lionfish, differences between the sexes become more apparent during courtship. Males become darker and more uniformly colored. Ripe females become paler, and a shiny, silvery line extends from the eyes continuing on a wart-like protrusion on the mandible. Unripe females retain their normal coloration (Fishelson 1975, 643). When a males finds a female that he is interested in, he will raise himself on his ventral fins and look up towards the water surface.
Then, he begins to circle the female, with the inward fin folded against the body, and the outward fin open and undulating. While the male is circling, the female will support herself, alternating between the ventral and pectoral fins, and move laterally away from the male. From there she may swim away, and the male may follow her. Fter the circling behavior, the male will slowly swim towards the surface, usually with the female close behind. While she is following him, the female trembles with her pectoral fins.
The pair may repeat this courtship ritual for 10 to 15 minutes without spawning (Fishelson 1975, 646-647). When the pair is ready to spawn, they remain close to the surface of the water. The male will use his body to push the female upwards, and often nips at the silvery protuberances on the female’s mandible. The spawning occurs while the pair is either swimming upside down near the surface, or they are swimming normally but with their caudal parts raised. The female releases two mucus tubes that, when seawater, turn into transparent balls 2 to 5 cm in diameter.
The eggs are embedded in this mucus, and are separated by the surrounding eggs by a separate sheet of mucus. Each ball of mucus may contain anywhere from 2,000 to 15,000 eggs, depending on the size of the female. The male expels his sperm at the same time that the female expels their eggs. The pair swims down immediately after spawning, and the male will begin searching for a new female to spawn. Females may be ready to spawn a few days later, which means that P. volitans can spawn uninterruptedly for months on end (Fishelson 1975, 647-649).
In their native range, lionfish spawn from June through December (Fishelson 1975,649), and in their invasive range, there is evidence that they are capable of spawning year round (Morris 2009, 20). III. Other Features One unique feature of P. volitans that may contribute to its success, both in its native and invasive ranges, is the venomous spines in its fins. There are venom glands along 13 dorsal spines, three anal spines, and two pelvic spines that extend about three quarters of the way up from the base to the tip (Morris 2009, 119).
Lionfish venom possesses a toxin containing acetylcholine, which impacts neuromuscular transmission, and can cause neuromuscular and cardiovascular effects in both humans and animals (Morris 2009, 119). This venom may help protect lionfish from predators, and may cause potential predators to avoid the species. There is even evidence that the Indo-Malayan octopus has been observed mimicking the lionfish, potentially as a way to protect against predation (Morris 2009, 128). There is also research that suggests that this venom may be useful for biomedical applications, such as reduction of cancer growth in humans (Morris 2009, 129).
