The longnose gar (Lepisosteus osseus), commonly referred to as the needlenose gar, is a species of ray-finned fish believed to have diverged from the rest of the Actinopterygii class long ago. Lepisosteiforme fossils have been found from the late Cretaceous period, about 66 million years ago, when they first evolved from a shared common ancestor with other teleost fish (McGrath, 2010). They have long, slender and usually spotted bodies with a thick armor of diamond shaped scales for protection. Their most distinctive feature, however, is their beak-like mouth from which it gets its name.
On average, gars have a lifespan of 17 years in the wild but can range anywhere between 15 and 20 years of age. Like most other vertebrates, gars are sexually dimorphic with females being the larger sex. Their behaviors displayed from the moment they hatch to their hunting tactics as adults shine a light on their unique life history and continuation as a species today.
HUNTING AND FEEDING
Longnose gars can feed at any time of day but prefer to hunt nocturnally (McCormack, 1969). They have been known to ambush their prey instead of chasing it down, a method that works best when diurnal species of fish are quiescent (McCormack, 1969). Gars have special adaptations such as a lateral line system that may help them sense prey in turbid waters and low light. The small hairs that make up this lateral line are able to detect vibrations and slight movements, guiding the predator in the direction of its prey.
After a potential prey has been detected, the gar will wait quietly near the surface of the water, keeping any movements to a minimum. To other fishes, the immobile gar looks like dead vegetation or a piece of wood. Although they do swim towards their prey, chasing after them introduces the problem of pushing the food item away in the predator’s attempt to swim forward. Suction feeding is a common solution, but not feasible due to the mouth morphology of the gars. Instead, gars will inconspicuously swim towards their prey sideways and attack from that angle. Swimming sideways allows the gar to move forward without creating much drag or resistance in the water. Additionally, this technique will prevent the prey from being pushed forward, minimizing both the predator’s time and effort in hunting. After attacking, the gar, using its jaw, will then turn its prey item so that it can be swallowed headfirst (McCormack, 1969).
In a study of the stomach content of longnose gars in Lake Texoma, a lake located on the shared border between Texas and Oklahoma, the ratio of fish to insects (including terrestrial invertebrates that are attracted to aquatic vegetation within gar territory) was approximately 9:1 (Echelle, 1968). This disparity can be explained in part by the gars’ previously mentioned preferred method of hunting as they transition from juveniles into adults with larger caloric requirements.
Schools of fish that stay near the surface of the water to feed are susceptible to predation in general but gars will most often hunt solitary or stray individuals (Echelle, 1968). Particular delicacies for adult gars include herrings, shads, and perches. Increased nocturnal swimming and foraging activity is also something observed most frequently in adult gars. The diurnal hunting of juveniles differs slightly from that of adults. Although they use many of the same techniques. Younger gars are less likely to feed at the water’s surface due to their tendency to hunt during the day when other fish are more alert. Juveniles begin to feed on small crustaceans and insect larvae at a young age. By the time they reach maturity (between 6-7 years after hatching for females and 2-3 years for males) they will have developed full-sized elongated mouths with sharp teeth adapted to piscivory (Echelle, 1968).
Different species of gars studied in the Brazos River, Texas showed preferences for different food types. While spotted gars (Lepisosteus oculatus) tend to consume the most abundant fish in its habitat, longnose gars in the river channels selected against smaller fish such as minnows almost entirely. Despite the smaller prey being available at all times, longnose gars tended to avoid them whenever possible to decrease they energy expenditure during hunting and instead went after fish that would provide a larger benefit given the costs (Robertson et al, 2007). This particular behavior of food selectivity is in accordance with the optimal foraging theory (OFT) model, which states that although an animal will obtain energy by consuming the prey it has hunted, the act of hunting itself requires time and energy that must be taken into account by the predator. Thus, a predator will choose prey that results in a net-positive return on energy (Pyke, 1984). Ultimately, the individual’s behavior while foraging will determine its survival and fitness.
BREATHING
Fluctuating environmental and habitat conditions can have an impact on gar behavior. For example, in poorly oxygenated waters, the gars’ highly vascularized swim bladder allows it to survive by breathing in atmospheric air (Icardo et al, 2015). Gars are able to control their buoyancy in water by inflating or deflating their swim bladder. The apical surface of their bladder is lined with mucociliated epithelium. The inside is covered by a respiratory epithelium that produces surfactant to keep the area of diffusion moist while capillary walls run along the respiratory surface to aid in gas exchange (Icardo et al, 2015). Although gars can use both structures (gills and the swim bladder) to breathe, in regions of low oxygen levels, they are able to cover their gills and use only the swim bladder to obtain all their oxygen (Icardo et al, 2015). Additionally, gars will often surface to exhale and inhale before returning underwater for longer periods of time (McCormack, 1969).
SPAWNING PREPARATION AND COURTSHIP
To reproduce, longnose gars travel away from their usual slow moving streams, rivers, and brackish waters in search of favorable environmental conditions (i.e. warm temperatures and high stream flow) for their eggs to thrive in. They migrate to smaller freshwater streams to spawn in fast moving streams with shallow riffles (Johnson and Noltie, 1996). Observations of their mating behaviors by Johnson and Noltie (1996) began as early as April and lasted until late May. Occurrences of matings were the most frequent when water levels and stream flow were high, however, these behaviors were less likely to be observed in colder temperatures. Some of these migrations to shallower, warmer waters may be “triggered” by a temperature minimum in their current location (Johnson and Noltie, 1996).
The mating rituals that gars partake in can involve various males all with the common goal of pursuing a single female. She will lead them to the spawning beds located in shallow water where the courting process can begin. The group of males swims around in an elliptical pattern for some time before one of the males nudges the female on her pectoral or lateral side to signal mating. The male’s total length, weight, and anal fin height all play a role in the female’s mate choice (McGrath, 2010).
Nests are not prepared by either sex and eggs are only deposited in convenient locations within the spawning beds themselves. The female will deposit her eggs in batches in different areas of the bed but the dominant male of the group will quickly fertilize them all at once and chase off the subordinates (Johnson and Noltie, 1996). Parental care is absent; however, there is an alternative method used by both sexes, involving brood parasitism, to increase the likelihood of offspring survival.
BROOD PARASITISM
A study of eggs from the nests of smallmouth bass (Micropterus dolomieu) revealed foreign eggs and larvae from an unknown species (Goff, 1984). These eggs were hatched at an aquaria and revealed to be longnose gars (Goff, 1984). In experiments, the longnose gar eggs were significantly larger than those of the bass, yet regardless of the size, appearance, or olfactory cues they released, the male smallmouth bass would protect everything in his nest, including the brood-parasitic gar eggs. Interspecific brood care is especially beneficial for the gars because adults do not particularly provide any sort of parental care following the process of fertilization.
While male bass are extremely territorial of their nests during the day, they become more quiescent at night. Adult gars take advantage of this opportunity to parasitize bass nests during this time. Male gars will court females like normal but instead of shedding her eggs for the male to fertilize in spawning beds, she will use the bass nests. The male bass will vigilantly guard the eggs, chasing off predators that he is able to take on but only while he is awake and alert. The disparity in size of the eggs in the bass nest will also often attract a great deal more predators (Goff, 1984). Other piscivores that would normally ignore the smaller eggs of the smallmouth bass are now more attracted to the nest. Gar eggs are toxic to humans but other aquatic species, they are the perfect prey item. For the bass, this means a greater chance of survival for their own young as gar eggs are usually the first if not the only ones to be eaten by predators (Goff, 1984).
Gars are primarily freshwater fish found only in North America. There are seven known species of gar, four species of which are within the genus Lepisosteus (Herrington et al., 2008). The other three species are in the genus are the spotted gar (L. oculatus), shortnose gar (L. platostomus) and the Florida gar (L. platyrhincus). Gars all have long slender bodies, beak-like jaws, and large, thick, diamond shaped scales. The longnose gar is easily distinguishable from other gar species by its extremely long and narrow snout (Kentucky Department of Fish & Wildlife, Gandy et al., 2012). Aside from snout length, a single row of sharp villiform teeth in the upper jaw distinguishes this species from the others (Gandy et al., 2012). Longnose gar bodies, like other gar species, are covered with rhomboidal ganoid scales. The outer layer of these scales is made of ganoin, a shiny substance that resembles enamel, and the inner layer is made of isopedine, which is composed of connective tissue embedded with bone, both penetrated by blood vessels.
Juvenile longnose gars have a pronounced broad, dark mid-lateral stripe that runs from the snout to the base of the caudal fin with a distinct white stripe directly below it, which is lost in adults. The typical coloration of adult longnose gar is olivaceous brown dorsally and laterally, fading into a pale yellow or white ventrally (Gandy et al., 2012). The longnose gar also has spots on its dorsal, anal, and caudal fins (Goddard 2010).
Sexual size dimorphism is the easiest way to tell males and females apart. Females are significantly larger than males before the spawning season. Most females then undergo weight loss during spawning, although it is not a significant weight loss. This weight loss is from the eggs they release (Johnson and Noltie, 1997). Males also tend to have larger mid-snout width, head width and anal-fin base length (McGrath and Hilton, 2012).
Although most wild-caught longnose gars fit the normal coloration patterns and can be identified using the diagnostic characteristics listed above, there are some exceptions. A study in 2008 recorded the first known lab-reared gar hybrids between a female longnose gar and a male alligator gar. These hybrids’ body coloration and transverse scale rows were similar to those of a longnose gar; snout length and shape fell between those of the longnose and alligator gars; and the hybrids had two rows of teeth on the upper jaw like alligator gars. Although no research has been done on wild longnose gar/ alligator gar hybrids, there are many claims by fishermen catching such individuals in some rivers of the southeastern United States (Herrington et al., 2008). Although there are other gar species that are more closely related to the longnose gar, there are not current studies documenting hybridization between those species and the longnose gar.
Melanistic deviations from the normal pattern have been found in individuals from river systems that drain into the Atlantic Ocean. These individuals range from entirely black with the typical pattern completely unidentifiable, to individuals with dark olivaceous, brown backs and black sides and venter. The cause of melanism is not a response to environmental factors, but rather genetically controlled (Woolcott and Kirk, 1975). Although Woolcott and Kirk’s findings support this claim because both melanistic and normally pigmented fish were taken from the same areas, others believe coloration varies in relation to water clarity, with individuals having a deeper green coloration and stronger brown hues in murky waters (Gandy et al., 2012).
In the Actinopterygii (ray-finned fish), morphological and molecular evidence support a subclass called the Neopterygii, which is composed of three extant clades: teleosts, amiids, and lepisosteids (Nelson 2006; Hurley et al. 2007). The longnose gar is classified as a lepisosteid in the Order Semionotiformes (Nelson 2006; Hurley et al. 2007). The amiids, or bowfins, are in Order Amiiformes with only one surviving species, Amia calva (Nelson 2006; Hurley et al. 2007). The teleosts (Order Teleosti) are the major lineage of ray-finned fish, having at least 23,453 species (Volff 2005).
Since they are descendants of the ancestral ray-finned fish, gars and bowfins share some common ancestor with teleosts (Groff and Youson 1997). Using morphological evidence, Geoff and Youson (1997) and Nelson (2006) concluded that gars diverged into a separate lineage before amiids and teleosts, indicating that amiids and teleosts are sister taxa, that in turn share a most-recent common ancestor with the gars. However, this phylogenetic relationship has been challenged by molecular data, which strongly support a gars/amiids sister taxa relationship, the Holostei, and the relationships have been debated since (Hurley et al. 2007).
Grande (2010) compared skeletal structures of all living and fossil gars, specifically focusing on the longnose and alligator gar as the type species for their respective genera, to attempt to resolve this evolutionary controversy. During this research, Grande (2010) recognized nine new fossil Lepisosteus, a new fossilized Lepisoteidae genus called Cuneatus, and a new fossilized family of gars, Obaichthyidae, that contains four species divided into two genera, Obaichthys and Dentilepisosteus. This research helped to support the hypothesis that bowfins and gars are indeed sister taxa based on shared skeletal similarities, including the loss of the pterotic bone in the ear and the presence of a supra angular bone in the jaw, paired vomer (facial bone), and large nasal process.
Developmental studies may also shed light on early branches of the Actinopterygian tree. Teleosts, bowfins, and gars all have spermatozoa without an anterior cap-like structure called an acrosome, suggesting that this is an ancestral character (Jaroszewska and Dabrowski 2009). In contrast, Jaroszewska and Dabrowski (2009) reviewed gar embryology studies from the nineteenth century, finding that gar development was different from bowfin and teleost development. This developmental difference suggested that bowfins and teleosts were sister taxa. Specifically, gar development differed because gars form a distinct layer of yolk called a periblast, and have surface cells that fold into the interior of the gastrula. Gars also go through mesoblastic or partial cleavage (Long and Ballard 2001). The similarities among their developmental characteristics supports that gars, bowfins, and teleosts are all part of the Neopterygii subclass.
To describe the evolutionary relationships among the gar species (i.e., Order Semionotiformes), several studies used molecular phylogenetics. Wright et al. (2012) used one mitochondrial gene and seven nuclear genes sequenced among the gars. Sipiorski (2011) used four mitochondrial loci and one nuclear locus for comparison. For his phylogenetic analysis, Cavin (2010) used 43 characters, including presence or absence of the basisphenoid (bone in base of cranium), interopercle (membrane bone between other gill bones), and opisthotic (bone in the ear).
Both Cavin (2010) and Sipiorski (2011) estimated that the last common ancestor of bowfins and gars lived 244 million years ago in the Middle Triassic Period, while Lepisosteidae diverged from other gar families 100 million years ago in the Cretaceous Period. The genus Lepisosteus diverged 50 million years ago in the Tertiary Period. Unlike Grande (2010) who placed the longnose gar as sister taxon to the spotted and Florida gar, with those three gars were sister to the shortnose gar, both Wright et al. (2012) and Sipiorski (2011) found that the longnose gar shared a more recent common ancestor with the shortnose gar, relative to the other gars in the study. Sipiorski (2011) estimated that shortnose and longnose gar diverged about 28 million years ago, while the spotted and Florida gar diverged approximately 23 million years ago, making them sister taxa to the shortnose and longnose gar.
Oguri (1987) examined the interrenal cells of longnose gar for comparison with cartilaginous and holostean fishes. In the gar, many scattered cells form the interrenal gland of the longnose gar on top of their kidney. Oguri (1987) discovered that the interrenal cells of longnose gar had numerous fat droplets. Although their specific function in longnose gar is unknown, the fat droplets most likely store and synthesize cholesterol (Jeon 2003). Such fat droplets are found in the cartilaginous fish (sharks: Chondrichthyes), but not in teleosts, suggesting that loss of fat droplets is a derived trait.
As a family, gars can breathe air, have a shortened heterocercal tail for more effective swimming, have ganoid scales, which are shaped like diamonds and coated with hard ganoin, and have some parts of a spiral valve in their small intestine that allows for increased nutrient absorption (McGrath 2010). Both bowfins and gars have a respiratory gas bladder that evolved to not only control their position in the water but also breathe in oxygen from the air (Graham 1997). Their respiratory gas bladder is similar to a flattened bag with a dorsal aorta located on top of it to provide adequate blood circulation (Lukáš 1989). Inside the gas bladder, smaller compartments and alveoli are created by many connecting septa composed of flat epithelial cells layered on top of muscle fibers for gas exchange. These characters help to further support gars as the sister taxa of bowfins.
The roe (external eggs) of the longnose (Lepisosteus osseus), spotted (Lepisosteus oculatus), and alligator (Atractosteus spatula) gars contain ichthyootoxin, a toxin known to be poisonous to at least laboratory mice, humans, and domesticated mammals (Colby 1943; Netsch and Witt 1962; Fuhrman et al. 1969). Of course, none of these vertebrates are natural predators of gar eggs, so they cannot speak to whether the toxin evolved as a predator defense. In contrast, several studies have been conducted to test the toxicity of ichthyootoxin on the natural predators of gar roe, including crayfish, sunfish, and catfish (Burns et al. 1981; Ostrand et al. 1996). Based on an experiment conducted by Burns et al. (1981), regardless of whether they were fed or injected with alligator gar roe extract, all crayfish (sex and species unknown due to immaturity) died within one day; more crayfish died from longnose gar roe than spotted gar roe within two days, suggesting that longnose gar roe had intermediate toxicity relative to alligator and spotted gar roe. Regardless of which gar’s toxin was used and crayfish mortality, after injection, all the crayfish experienced short-term changes in behavior, including overall joint stiffness in walking, restlessness, twitching of back legs, and loss of coordination in movement (Burns et al. 1981). Crayfish are likely predators on longnose gar roe because there are often many young crayfish in the places where longnose gar spawn, so the toxin may act to protect roe against these predators and increase the fitness of the parents whose roe are toxic (Burns et al. 1981). Thus, toxic eggs are probably adaptive. In addition, roe toxicity may be an adaptation to crayfish because longnose gar have more visibly colored eggs and spawn in sparsely vegetated locations, decreasing the longnose gar roe’s crypticity and increasing its predator vulnerability (Burns et al. 1981). Since fish are also visual predators, experiments that use longnose gar roe instead of alligator gar roe are needed to test whether predatory fish are affected by longnose gar ichthyootoxin. Further research to examine the potential evolutionary relationship between roe color and ichthyootoxin has not been conducted, so whether longnose gar roe color is an aposematic signal or not is currently unknown.
Although crayfish mortality was high in those crayfish that ate gar roe, alligator gar roe did not cause any bluegill sunfish deaths (Burns et al. 1981). Alligator gar roe was the most toxic of the three gar species tested, according to the crayfish survey; thus, it is unlikely that the less toxic longnose gar roe causes mortality in bluegill sunfish, though this was not tested directly, and vertebrate reactions to toxins are likely to differ from that of invertebrates. However, assuming that longnose gar roe does not cause any negative side effects or death of predatory fish, the data suggest that ichthyootoxic gar roe likely evolved as an adaptation to crayfish predation and that fish predation on gar eggs is a weaker selective force.
Consistent with this generalization, Netsch and Witt (1962) found that the roe of a different gar (shortnose gar) did not cause mortality in bluegill sunfish (Lepomis macrochirus) or another predatory fish (northern river carpsucker; Carpiodes carpio). Similarly, Ostrand et al. (1996) fed spotted gar roe to green sunfish (Lepomis cyanellus) and channel catfish (Ictalurus punctatus), and both predatory fish survived, so it seemed that the spotted gar roe toxin had no effect on the predatory fish. Both predatory fish had no measured weight loss, and some even gained weight, indicating that spotted gar roe may be part of their natural prey (Ostrand et al. 1996). Therefore, Ostrand et al. (1996) concluded that spotted gar toxin was unlikely to be used as a method of defense against fish and that the toxin might have been the result of a mutation in another chemical compound that had widespread (pleiotropic) effects, being toxic to crayfish, thereby, through chance. However, since the experiments did not test longnose gar roe, which had potentially greater toxicity than the spotted gar roe, further studies are needed to clarify whether longnose gar roe ichthyootoxin is adaptive for specific or general predator protection, exists for some other function, or is the result of drift and contingency. The location of the longnose gar in its phylogeny allows further speculation of the role of ichthyootoxin.
Within the Class Osteichthyes, or the bony fish, longnose gars are an early branch of Actinopterygii, or ray-finned fish (Alfaro et al. 2008). Longnose gars (L. osseous) are a member of the genus Lepisosteus along with three other species, including the shortnose gar (L. platostomus), spotted gar (L. oculatus), and Florida gar (L. platyrhincus) (Alfaro et al. 2008). Besides the genus Lepisosteus, the gar family, Lepisosteidae, includes the genus Atractosteus, which is composed of the alligator gar (A. spatula), Cuban gar (A. tristoechus), and tropical gar (A. tropicus) (Alfaro et al. 2008). Since longnose gar are in the same genus as the shortnose and spotted gar and the same family as alligator gar, and none of the species caused any negative effects on fish predators, it is likely that ichthyootoxin is an evolutionarily shared trait at least at the family level. If ichthyootoxin is an evolutionarily shared trait, then it cannot be considered a derived trait that only longnose gar have and supports that it is not a functional adaptation in longnose gar. However, since longnose gar roe has not been experimentally fed to predatory fish, if future experiments conducted on longnose gar roe show that they cause predatory fish mortality, it would suggest that ichthyootoxin evolved further in longnose gar to protect their roe from predatory fish.
The roe (external eggs) of the longnose (Lepisosteus osseus), spotted (Lepisosteus oculatus), and alligator (Atractosteus spatula) gars contain ichthyootoxin, a toxin known to be poisonous to at least laboratory mice, humans, and domesticated mammals (Colby 1943; Netsch and Witt 1962; Fuhrman et al. 1969). Of course, none of these vertebrates are natural predators of gar eggs, so they cannot speak to whether the toxin evolved as a predator defense. In contrast, several studies have been conducted to test the toxicity of ichthyootoxin on the natural predators of gar roe, including crayfish, sunfish, and catfish (Burns et al. 1981; Ostrand et al. 1996). Based on an experiment conducted by Burns et al. (1981), regardless of whether they were fed or injected with alligator gar roe extract, all crayfish (sex and species unknown due to immaturity) died within one day; more crayfish died from longnose gar roe than spotted gar roe within two days, suggesting that longnose gar roe had intermediate toxicity relative to alligator and spotted gar roe. Regardless of which gar’s toxin was used and crayfish mortality, after injection, all the crayfish experienced short-term changes in behavior, including overall joint stiffness in walking, restlessness, twitching of back legs, and loss of coordination in movement (Burns et al. 1981). Crayfish are likely predators on longnose gar roe because there are often many young crayfish in the places where longnose gar spawn, so the toxin may act to protect roe against these predators and increase the fitness of the parents whose roe are toxic (Burns et al. 1981). Thus, toxic eggs are probably adaptive. In addition, roe toxicity may be an adaptation to crayfish because longnose gar have more visibly colored eggs and spawn in sparsely vegetated locations, decreasing the longnose gar roe’s crypticity and increasing its predator vulnerability (Burns et al. 1981). Since fish are also visual predators, experiments that use longnose gar roe instead of alligator gar roe are needed to test whether predatory fish are affected by longnose gar ichthyootoxin. Further research to examine the potential evolutionary relationship between roe color and ichthyootoxin has not been conducted, so whether longnose gar roe color is an aposematic signal or not is currently unknown.
Although crayfish mortality was high in those crayfish that ate gar roe, alligator gar roe did not cause any bluegill sunfish deaths (Burns et al. 1981). Alligator gar roe was the most toxic of the three gar species tested, according to the crayfish survey; thus, it is unlikely that the less toxic longnose gar roe causes mortality in bluegill sunfish, though this was not tested directly, and vertebrate reactions to toxins are likely to differ from that of invertebrates. However, assuming that longnose gar roe does not cause any negative side effects or death of predatory fish, the data suggest that ichthyootoxic gar roe likely evolved as an adaptation to crayfish predation and that fish predation on gar eggs is a weaker selective force.
Consistent with this generalization, Netsch and Witt (1962) found that the roe of a different gar (shortnose gar) did not cause mortality in bluegill sunfish (Lepomis macrochirus) or another predatory fish (northern river carpsucker; Carpiodes carpio). Similarly, Ostrand et al. (1996) fed spotted gar roe to green sunfish (Lepomis cyanellus) and channel catfish (Ictalurus punctatus), and both predatory fish survived, so it seemed that the spotted gar roe toxin had no effect on the predatory fish. Both predatory fish had no measured weight loss, and some even gained weight, indicating that spotted gar roe may be part of their natural prey (Ostrand et al. 1996). Therefore, Ostrand et al. (1996) concluded that spotted gar toxin was unlikely to be used as a method of defense against fish and that the toxin might have been the result of a mutation in another chemical compound that had widespread (pleiotropic) effects, being toxic to crayfish, thereby, through chance. However, since the experiments did not test longnose gar roe, which had potentially greater toxicity than the spotted gar roe, further studies are needed to clarify whether longnose gar roe ichthyootoxin is adaptive for specific or general predator protection, exists for some other function, or is the result of drift and contingency. The location of the longnose gar in its phylogeny allows further speculation of the role of ichthyootoxin.
Within the Class Osteichthyes, or the bony fish, longnose gars are an early branch of Actinopterygii, or ray-finned fish (Alfaro et al. 2008). Longnose gars (L. osseous) are a member of the genus Lepisosteus along with three other species, including the shortnose gar (L. platostomus), spotted gar (L. oculatus), and Florida gar (L. platyrhincus) (Alfaro et al. 2008). Besides the genus Lepisosteus, the gar family, Lepisosteidae, includes the genus Atractosteus, which is composed of the alligator gar (A. spatula), Cuban gar (A. tristoechus), and tropical gar (A. tropicus) (Alfaro et al. 2008). Since longnose gar are in the same genus as the shortnose and spotted gar and the same family as alligator gar, and none of the species caused any negative effects on fish predators, it is likely that ichthyootoxin is an evolutionarily shared trait at least at the family level. If ichthyootoxin is an evolutionarily shared trait, then it cannot be considered a derived trait that only longnose gar have and supports that it is not a functional adaptation in longnose gar. However, since longnose gar roe has not been experimentally fed to predatory fish, if future experiments conducted on longnose gar roe show that they cause predatory fish mortality, it would suggest that ichthyootoxin evolved further in longnose gar to protect their roe from predatory fish.
The roe (external eggs) of the longnose (Lepisosteus osseus), spotted (Lepisosteus oculatus), and alligator (Atractosteus spatula) gars contain ichthyootoxin, a toxin known to be poisonous to at least laboratory mice, humans, and domesticated mammals (Colby 1943; Netsch and Witt 1962; Fuhrman et al. 1969). Of course, none of these vertebrates are natural predators of gar eggs, so they cannot speak to whether the toxin evolved as a predator defense. In contrast, several studies have been conducted to test the toxicity of ichthyootoxin on the natural predators of gar roe, including crayfish, sunfish, and catfish (Burns et al. 1981; Ostrand et al. 1996). Based on an experiment conducted by Burns et al. (1981), regardless of whether they were fed or injected with alligator gar roe extract, all crayfish (sex and species unknown due to immaturity) died within one day; more crayfish died from longnose gar roe than spotted gar roe within two days, suggesting that longnose gar roe had intermediate toxicity relative to alligator and spotted gar roe. Regardless of which gar’s toxin was used and crayfish mortality, after injection, all the crayfish experienced short-term changes in behavior, including overall joint stiffness in walking, restlessness, twitching of back legs, and loss of coordination in movement (Burns et al. 1981). Crayfish are likely predators on longnose gar roe because there are often many young crayfish in the places where longnose gar spawn, so the toxin may act to protect roe against these predators and increase the fitness of the parents whose roe are toxic (Burns et al. 1981). Thus, toxic eggs are probably adaptive. In addition, roe toxicity may be an adaptation to crayfish because longnose gar have more visibly colored eggs and spawn in sparsely vegetated locations, decreasing the longnose gar roe’s crypticity and increasing its predator vulnerability (Burns et al. 1981). Since fish are also visual predators, experiments that use longnose gar roe instead of alligator gar roe are needed to test whether predatory fish are affected by longnose gar ichthyootoxin. Further research to examine the potential evolutionary relationship between roe color and ichthyootoxin has not been conducted, so whether longnose gar roe color is an aposematic signal or not is currently unknown.
Although crayfish mortality was high in those crayfish that ate gar roe, alligator gar roe did not cause any bluegill sunfish deaths (Burns et al. 1981). Alligator gar roe was the most toxic of the three gar species tested, according to the crayfish survey; thus, it is unlikely that the less toxic longnose gar roe causes mortality in bluegill sunfish, though this was not tested directly, and vertebrate reactions to toxins are likely to differ from that of invertebrates. However, assuming that longnose gar roe does not cause any negative side effects or death of predatory fish, the data suggest that ichthyootoxic gar roe likely evolved as an adaptation to crayfish predation and that fish predation on gar eggs is a weaker selective force.
Consistent with this generalization, Netsch and Witt (1962) found that the roe of a different gar (shortnose gar) did not cause mortality in bluegill sunfish (Lepomis macrochirus) or another predatory fish (northern river carpsucker; Carpiodes carpio). Similarly, Ostrand et al. (1996) fed spotted gar roe to green sunfish (Lepomis cyanellus) and channel catfish (Ictalurus punctatus), and both predatory fish survived, so it seemed that the spotted gar roe toxin had no effect on the predatory fish. Both predatory fish had no measured weight loss, and some even gained weight, indicating that spotted gar roe may be part of their natural prey (Ostrand et al. 1996). Therefore, Ostrand et al. (1996) concluded that spotted gar toxin was unlikely to be used as a method of defense against fish and that the toxin might have been the result of a mutation in another chemical compound that had widespread (pleiotropic) effects, being toxic to crayfish, thereby, through chance. However, since the experiments did not test longnose gar roe, which had potentially greater toxicity than the spotted gar roe, further studies are needed to clarify whether longnose gar roe ichthyootoxin is adaptive for specific or general predator protection, exists for some other function, or is the result of drift and contingency. The location of the longnose gar in its phylogeny allows further speculation of the role of ichthyootoxin.
Within the Class Osteichthyes, or the bony fish, longnose gars are an early branch of Actinopterygii, or ray-finned fish (Alfaro et al. 2008). Longnose gars (L. osseous) are a member of the genus Lepisosteus along with three other species, including the shortnose gar (L. platostomus), spotted gar (L. oculatus), and Florida gar (L. platyrhincus) (Alfaro et al. 2008). Besides the genus Lepisosteus, the gar family, Lepisosteidae, includes the genus Atractosteus, which is composed of the alligator gar (A. spatula), Cuban gar (A. tristoechus), and tropical gar (A. tropicus) (Alfaro et al. 2008). Since longnose gar are in the same genus as the shortnose and spotted gar and the same family as alligator gar, and none of the species caused any negative effects on fish predators, it is likely that ichthyootoxin is an evolutionarily shared trait at least at the family level. If ichthyootoxin is an evolutionarily shared trait, then it cannot be considered a derived trait that only longnose gar have and supports that it is not a functional adaptation in longnose gar. However, since longnose gar roe has not been experimentally fed to predatory fish, if future experiments conducted on longnose gar roe show that they cause predatory fish mortality, it would suggest that ichthyootoxin evolved further in longnose gar to protect their roe from predatory fish.
The longnose gar (Lepisosteus osseus) inhabits a wide variety of aquatic ecological niches, occurring frequently in slow moving areas such as backwaters, quiet currents, and sluggish areas of water close to vegetation (Goodyear 1967).They tend to prefer shallow and weedy areas of medium to large rivers (typically over 12m in width), lakes, estuaries, reservoirs, and can occasionally be found in the brackish waters of coastal inlets and deeper stretches of bayou habitat along the Gulf Coast (Goodyear 1967). Some longnose gars are even known to use sewers to travel from larger bodies of water such as lakes and rivers to smaller ponds and streams. Despite this great variation in habitat use, however, they tend to prefer areas with wide floodplains where seasonally shallow waters provide their young with some protection from predators (Becker, 1983).
Spawning L. osseus often congregate near the surface in littoral shallows, and spawning can occur over vegetated beds on river banks, in grasses and weeds in shoal water in lakes, or near stone piles of railroad bridges or gravel bars in streams.The eggs require areas of low flow water to keep from getting washed away, as they have a minimal adhesive substance keeping them in place. As they mature, young gar tend to occupy shallows, and larger individuals can be found in deeper waters of pools, backwaters, and oxbows of medium to large rivers and lakes (Becker, 1983). For many gar species, human construction and agriculture have dramatically altered their riverine ecosystems.The loss of aquatic vegetation, increase of sedimentation, and contamination in the freshwater systems in North America has largely eliminated their preferred spawning habitats (Jean, 1946). This loss of habitat has contributed to population declines across much of the animal’s range.
Gars have unique physical modifications that allow them to survive in limnetic environments typically unsuitable for other species of fish. They are capable of gulping air into their swim bladders, which provides a secondary method of oxygen intake that most fish do not possess (Rahn et al. 1971). Because they do not exclusively rely on getting oxygen through their gills, gars can survive in waters with oxygen levels too low for many other species, and sometimes even through temporary, total oxygen depletion.
In general, the family Lepisosteidae is currently known to inhabit fresh, brackish, and occasionally marine waters in Eastern North America, Central America, and Cuba (Wiley, 1976). Within North America, the longnose gar is found east of the Mississippi River from Canada all the way down to Florida, and as far west as Kansas, Texas, and southern New Mexico. Lepiosteus osseus inhabits the drainage basins of the Mississippi River, Lake Michigan, and Lake Superior, and is extremely common in Mississippi, Ohio and Wisconsin rivers. However, fossils indicate that the family’s range in used to be much larger. Fossil Lepisostids from the Mesozoic and Cenozoic eras are found in Europe, India, South America and North America (Wiley, 1976).
Extensive studies on the distribution of L. osseus have been completed in Wisconsin, indicating specific rivers and lakes in which they can be found (Haase, 1969 and Becker, 1983). These studies in Wisconsin also found different substrates associated with L. osseus habitat. The frequency of substrates associated with L. osseus is 29% gravel, 25% sand, 17% mud, 13% clay, 8% silt, 4% rubble, and 4% boulders, with the percentage values representing the proportion of time longnose gar are found in habitats composed of the substrates (Becker, 1983).Current research on the longnose gar is lacking, so it is unclear whether this frequency distribution is uniform across all habitats.
The longnose gar (Lepisosteus osseus) is a member of the family Lepisosteidae, a group of freshwater fishes collectively known as garfish that are most closely related to bowfins in the infraclass Holostei. Within the genus Lepisosteus, which contains four species, the longnose and shortnose (Lepisosteus platostomus) gars are more closely related to each other and are sister taxa to the Spotted (Lepisosteus oculatus) and Florida (Lepisosteus platyrhincus) Gars. The longnose gar is primarily a freshwater fish, with some populations existing in brackish waters and very few in marine environments. Typical gar habitat consists mainly of slow moving rivers, lakes, and other bodies of water where water is shallow and vegetation is present. The longnose gar is found in North America, from southern portions of Quebec all the way down to Cuba. Total adult population size is unknown but is likely greater than 100,000. In comparison to other gar species, the longnose gar is easily distinguishable by its extremely long and narrow snout. Aside from snout length, a single row of sharp villiform or small and slender teeth in the upper jaw allows this species to be easily distinguished. The typical coloration of an adult longnose gar is olivaceous brown dorsally and laterally, which fades into a pale yellow or white ventrally. The longnose gar also has spots on its dorsal, anal, and caudal fins. Similar to other gars, longnose gar roe (external eggs) contains ichthyootoxin, but scientists are uncertain as to whether the toxin has evolved for egg defense or as a byproduct of other processes during development. Crayfish that eat longnose gar roe are negatively affected and can die, but other natural predators, like sunfish, are not affected. Gars are generally considered nuisances by fisherman because of their consumption of and competition with game species and their tendency to become entangled in nylon nets. Gars are carnivores but not necessarily strict piscivores. The diet of these nocturnal hunters consists of smaller fish such as herrings and shads but will also include insect larvae until gars have reached adult age. Gars both feed and breed in shallow waters. Female gars shed their eggs in occupied nests of smallmouth bass, allowing male smallmouth bass to provide parental care and protection that they themselves do not provide.
Lepisosteus osseus has been present in North America for over 100 million years, and is currently distributed throughout the eastern two-thirds of the United States (Johnson and Noltie, 1997, Sutton et al., 2009). Populations inhabit watersheds in the St. Lawrence River drainage, the Atlantic coast from New Jersey to Florida, the Great Lakes and Mississippi River system, and as far west as the Rio Grande River drainage (Gilbert and Williams, 2002). Longnose gar typically inhabit freshwater, although individuals have been caught at salinities as high as 33 practical salinity units (1 psu=1g/kg), (Gandy et al., 2012). Longnose gar occurs naturally through Florida, but there is no record of its presence in natural habitats in extreme southern Florida, including the Everglades. In southern Florida they only appear in man-made canals. The source population for the gars in the canals is hypothesized to be from Lake Okeechobee due to its connectivity to south Florida’s canals, but the exact source is still unknown (Gandy et al., 2012). Total adult population size is unknown but likely greater than 100,000 across the entire range (Page and Burr 2011).
Reproduction takes place from April to August, varying with temperature differences in different geographic areas (McGrath et al., 2012). During reproduction, longnose gars migrate to small, clear, faster moving streams to spawn. Even lacustrine longnose gars make such migrations, traveling into lake tributaries to spawn (McGrath et al., 2012). Spawning migrations are triggered by changes in temperature. Once lake temperatures pass a minimum threshold between 15°C and 16.7°C, longnose gars begin migrating to their stream spawning sites (Johnson and Noltie, 1997). During spawning one female is usually accompanied by two to four males that swim alongside her. She releases her eggs, which are fertilized by the males before sinking to the bottom and sticking to the substrate. Egg counts can range from 30,000 to 77,000 from a single fish during a spawning event; these egg counts are positively correlated to fish length (Holloway, 1954). The eggs then hatch in three to nine days, depending on water temperature (Goddard 2010).
In a river population of longnose gars, the average age is between 3 and 7 and individuals can live to be up to 16 years old. Longnose gars are estimated to live anywhere between 4 and 10 years (Sutton et al., 2009) and the age of reproductive maturity is estimated to be from 3 to 4 years old for males while females do not mature until 6 years (Goddard 2010). Residence times at spawning sites range from 15 to 94 days, with males staying longer than females (McGrath et al., 2012). But, complete residency times from this particular study were underestimates because it is unknown when the fish first arrived at the spawning site ((McGrath et al., 2012). After spawning, individuals have been recorded relocating from freshwater regions, traveling through brackish water, to another freshwater region at distances up to 74 km (McGrath et al., 2012). Juvenile gars primarily use shallow backwater pools that support aquatic macrophytes. Adults use these areas as well as larger deeper riverine pool habitats (Sutton et al., 2009).
The sex ratio of adult spawning longnose gar populations is male biased (between 1.67:1 to 2.07:1). This is statistically significantly skewed in comparison with populations assessed outside of the spawning season, in which the sex ratio is closer to 1:1 (Johnson and Noltie 1997).
Gars are well known among fishermen and boaters in North America because they regularly occur in the same areas as game fish and are frequently spotted “breaking” the surface (a behavior associated with gulping air), making them much more visible to fisherman than other species. Historically, gars have been regarded as a nuisance species to fisherman because they can damage lures and nets with their small sharp teeth and are considered predators of more desirable game fish.They have been studied very little compared to other fish, even though recreational and commercial fisheries currently exist for several species of gar.Because of their predation of game fish, gar management has long emphasized removing the species (Johnson and Nolte, 1997). However, other recent management consideration has promoted higher populations of gars as a possible means of controlling the overpopulation of sunfish and yellow perch (Niemuth et al., 1959).
Threats to Lepisosteus osseus populations are mainly the result of human manipulation of aquatic ecosystems. The species is also affected by overfishing via bycatch, habitat loss, dams, road construction, pollution, and other human caused destruction of these systems. The damage to the shorelines of aquatic ecosystems can be extremely harmful to their breeding process, since eggs are generally laid in shallow water and young gar spent a majority of their time in shallow vegetated areas (Scarnecchia, 1992). The species is also often unintentionally caught in many types of fishing nets and seines. In some states, L. osseus has been classified as a threatened species (South Dakota, Delaware, and Pennsylvania).
About the longnose gar, in the flowery language of the era, Forbes and Richardson (1920) stated: “[the longnose gar] is a wholly worthless and destructive nuisance in relation to mankind. It has, in fact, all of the vices and none of the virtues of a predaceous fish.” That is, longnose gar were long considered rough fish (or “trash fish”) due to how undesirable they were to anglers and sport fisherman (Spitzer 2010).In recent times, however, the longnose gar has become more of a sport fish and some people have found their meat to be appetizing.There is a commercial fishery for longnose gar in Arkansas, and the species has been taken from the Wisconsin and Mississippi rivers as well (Becker, 1983). The typical method of purposeful capture is entangling the teeth in nylon threads of a net or by bow fishing using specialized archery equipment. In Texas, specimens in excess of 80 pounds have been landed using a bow and arrow (Texas Parks and Wildlife). Some ethnic groups in Louisiana and in the southern US eat the meat of longnose gar, forgoing filleting (due to the hassle of sorting through lots of small bones) to roll the meat into “gar balls”.
It should be noted that gar eggs may be highly toxic to mammals and birds if ingested (Niemuth et al., 1959).The toxin has yet to be identified, but current speculation is that the toxin is a protein of some kind, potentially an algaecide or fungicide.Surprisingly though, gar eggs have not been shown to be toxic to any other fish species.
Gar skins consist of ganoid scales, which provide a sturdy, bony frame, and thus have been used to a small extent as luxury items; e.g., picture frames, purses, and fancy boxes (Forbes and Richardson, 1920). The hard bony plates in the skin were also used by Native Americans as arrowheads, and native Caribbean people used the skin for breastplates. There are records of Creek and Chickasaw people having ritual “Gar Fish Dances”.The Gar Fish Dance is considered the only true surviving Chickasaw dance and occurs during a ceremony in which the teeth of a gar are used in purification rituals (Spitzer 2010). Even early American pioneers have records of covering the blades of their plows in gar skins.
