Gar Species Research Articles

A giant bowfin from a Paleocene hothouse ecosystem in North America

Abstract Aquatic biodiversity changed dramatically at the start of the Paleogene. Although comparatively little is known about global freshwater ecosystems that appeared just after the Cretaceous–Paleogene mass extinction, available data suggest that they were buffered from the worst effects of the extinction event. Here, we describe a nearly complete skeleton of a large-bodied ray-finned fish from a wetland ecosystem that existed fewer than 10 Myr after the end-Cretaceous extinction in western North America. With a maximum length likely exceeding 2 m, †Amia basiloides sp. nov. is one of the largest species in Holostei, a once species-rich clade of ray-finned fishes now survived by the nine living species of gars and bowfins. High-resolution computed tomography scans illuminate the anatomy of †A. basiloides and suggest it was an analogue of living large-bodied, piscivorous freshwater fishes found in the Southern Hemisphere and southern North America. When considered in a phylogenetic context, †A. basiloides shows that close relatives of living bowfins rapidly achieved gigantism in the Early Paleogene of North America after the largest members of an ancient clade closely related to bowfins went extinct. Although the Cretaceous–Paleogene boundary likely induced turnover of freshwater vertebrate predatory guilds, holostean faunas remained ecologically comparable across the extinction due to exceptionally fast episodes of convergence.

The genomic signatures of evolutionary stasis.

Evolutionary stasis characterizes lineages that seldom speciate and show little phenotypic change over long stretches of geological time. Although lineages that appear to exhibit evolutionary stasis are often called living fossils, no single mechanism is thought to be responsible for their slow rates of morphological evolution and low species diversity. Some analyses of molecular evolutionary rates in a handful of living fossil lineages have indicated that these clades exhibit slow rates of genomic change. Here, we investigate mechanisms of evolutionary stasis using a dataset of 1,105 exons for 481 vertebrate species. We demonstrate that two ancient clades of ray-finned fishes classically called living fossils, gars and sturgeons, exhibit the lowest rates of molecular substitution in protein-coding genes among all jawed vertebrates. Comparably low rates of evolution are observed at fourfold degenerate sites in gars and sturgeons, implying a mechanism of stasis decoupled from selection that we speculate is linked to a highly effective DNA repair apparatus. We show that two gar species last sharing common ancestry over 100 million years ago produce morphologically intermediate and fertile hybrids in the wild. This makes gars the oldest naturally hybridizing divergence among eukaryotes and supports a theoretical prediction that slow rates of nucleotide substitution across the genome slow the accumulation of genetic incompatibilities, enabling hybridization across deeply divergent lineages and slowing the rate of speciation over geological timescales. Our results help establish molecular stasis as a barrier to speciation and phenotypic innovation and provide a mechanism to explain the low species diversity in living fossil lineages.

Phylogenomics of the Ancient and Species-Depauperate Gars Tracks 150 Million Years of Continental Fragmentation in the Northern Hemisphere.

Reconstructing deep-time biogeographic histories is limited by the comparatively recent diversification of most extant lineages. Ray-finned fishes, which include nearly half of all living vertebrates, are no exception. Although most lineages of ray-finned fishes radiated around the Cretaceous-Paleogene boundary, a handful of ancient, species-poor clades still persist. These lineages can illuminate very old biogeographic trends, but their low species richness can also limit the reconstruction of these patterns. The seven extant species of gars distributed in freshwater habitats in North America and Cuba are an old clade with a fossil record spanning over 150 million years of Earth history. Using a genomic data set of DNA sequences of 1105 exons for the seven living species and an updated morphological matrix of all extant and extinct taxa, we infer the phylogenetic relationships of gars and test how divergence times and biogeographic reconstructions are influenced by sequential and joint estimation and the effect on these inferences when using different taxon sets based on fossil completeness. Our analyses consistently show that the two extant gar genera Atractosteus and Lepisosteus diverged approximately 105 million years ago and many of the inferred divergences in the gar time-calibrated phylogeny closely track major Mesozoic tectonic events, including the separation of the Americas, the expansion of the early Atlantic, and the Cretaceous reorganization of North American river systems. The crown clades Atractosteus and Lepisosteus originated in the Cenozoic of eastern North America, implying that this region has served as both the origin of extant gar diversity and the refugium of this iconic ancient lineage. These results exemplify how combining phylogenomics with the fossil record provides congruence around the evolutionary history of ancient clades like gars and can reveal long-lost biogeographic patterns. [Lepisosteidae; fossilized birth death; biogeography; phylogenomics; paleontology.].

Characterization of the G protein-coupled receptor family SREB across fish evolution

The SREB (Super-conserved Receptors Expressed in Brain) family of G protein-coupled receptors is highly conserved across vertebrates and consists of three members: SREB1 (orphan receptor GPR27), SREB2 (GPR85), and SREB3 (GPR173). Ligands for these receptors are largely unknown or only recently identified, and functions for all three are still beginning to be understood, including roles in glucose homeostasis, neurogenesis, and hypothalamic control of reproduction. In addition to the brain, all three are expressed in gonads, but relatively few studies have focused on this, especially in non-mammalian models or in an integrated approach across the entire receptor family. The purpose of this study was to more fully characterize sreb genes in fish, using comparative genomics and gonadal expression analyses in five diverse ray-finned (Actinopterygii) species across evolution. Several unique characteristics were identified in fish, including: (1) a novel, fourth euteleost-specific gene (sreb3b or gpr173b) that likely emerged from a copy of sreb3 in a separate event after the teleost whole genome duplication, (2) sreb3a gene loss in Order Cyprinodontiformes, and (3) expression differences between a gar species and teleosts. Overall, gonadal patterns suggested an important role for all sreb genes in teleost testicular development, while gar were characterized by greater ovarian expression that may reflect similar roles to mammals. The novel sreb3b gene was also characterized by several unique features, including divergent but highly conserved amino acid positions, and elevated brain expression in puffer (Dichotomyctere nigroviridis) that more closely matched sreb2, not sreb3a. These results demonstrate that SREBs may differ among vertebrates in genomic structure and function, and more research is needed to better understand these roles in fish.

Feeding Ecology of Age‐0 Gar at Texoma Reservoir Inferred from Analysis of Stable Isotopes

AbstractConservation and restoration of gar (Lepisosteidae) populations in North America are increasingly of interest to fisheries managers. Alligator Gar Atractosteus spatula are being stocked as age‐0 fish in efforts to re‐establish extirpated populations. However, gars are known to be highly cannibalistic in hatcheries, suggesting that age‐0 Alligator Gar introduced into natural habitats may face predation pressures from other gar species, limiting the likelihood of released fish recruiting to the population. Furthermore, introduced age‐0 gar may not have the proper prey resources for rapid growth that would facilitate recruitment to adulthood. Texoma Reservoir, located on the Oklahoma–Texas border, hosts four native gar species, including the Alligator Gar, whose population is supported by supplemental stocking of age‐0 fingerlings. We investigated feeding by age‐0 gar to obtain a baseline level of trophic ecology for this group of fishes, including the potential for poststocking cannibalism. Food webs were reconstructed via analysis of carbon (δ13C) and nitrogen (δ15N) isotopes using Bayesian mixing model approaches. Isotopic values for age‐0 fish of all four gar species were similar. Invertebrates represented a large fraction of the diet for all gars, followed by Common Carp Cyprinus carpio and Grass Carp Ctenopharyngodon idella. Competitive interactions among Bluegill Lepomis macrochirus, White Bass Morone chrysops, White Crappie Pomoxis annularis, and young gar may occur for invertebrates, shads Dorosoma spp., and Western Mosquitofish Gambusia affinis but are likely short‐lived due to the rapid growth of age‐0 gar after their transition to piscivory. Trophic position of age‐0 Alligator Gar, Longnose Gar Lepisosteus osseus, and Spotted Gar Lepisosteus oculatus was positively related to TL, but this relationship was not observed for Shortnose Gar Lepisosteus platostomus. In Texoma Reservoir, the four native gar species, including stocked Alligator Gar, appear to have adequate food resources for recruitment, with little indication of within‐family or interspecific predation. This suggests that stocked Alligator Gar quickly acclimated to their new environment.

Possible Large-Scale Hybridization and Introgression Between Longnose Gar (Lepisosteus osseus) and Shortnose Gar (Lepisosteus platostomus) in The Fox River Drainage, Wisconsin

Hybridization among gar species (Pisces: Family Lepisosteidae) has only recently been documented, and relatively few occurrences have been reported. In the Fox River drainage of the Lake Michigan Basin in Wisconsin, apparent hybrids and introgressed individuals (hereafter “hybrids”) of Longnose Gar (Lepisosteus osseus) and Shortnose Gar (L. platostomus) were widespread and numerous, constituting about 44% of the total gar population. Presumed hybrids could be readily distinguished by either their intermediate ratio of snout length to snout width or a low ratio, characteristic of Shortnose Gar, coupled with the presence of conspicuous spots on the top of the snout, an occasional Longnose Gar characteristic. Presumed hybrids had genetic matrilines (cytochrome b) of either Shortnose or Longnose Gar. Apparent hybrids occur commonly throughout the Fox River drainage, including the upper and lower Fox River, its major tributary the Wolf River, the riverine lakes Poygan, Winneconne, Butte des Morts, Winnebago, and Little Butte des Morts, and Green Bay, Lake Michigan, near the mouth of the lower Fox River. Evidence exists for possible hybrids in the adjacent Mississippi River basin and the Missouri River basin, but they appear to be less common and more localized. Extensive hybridization and introgression in the Fox River drainage may have been facilitated by the close phylogenetic relationship of Longnose and Shortnose Gar, the much greater abundance of Longnose relative to Shortnose Gar in the Fox River drainage, the apparent relatively recent colonization of the Fox River drainage by the Shortnose Gar, and the substantial modification and loss of gar spawning habitat in the Fox River drainage caused by dams and artificial water level regulation.

Occurrence and Co‐Occurrence Patterns of Gar in River–Floodplain Habitats: Methods to Leverage Species Coexistence to Benefit Distributional Models

AbstractHabitat segregation and hypothesized biotic interactions among coexisting gar species may confound attempts to describe the distributions of these species by using only macrohabitat availability in the presence of conspecifics. However, the strength of interactions among gar species and the spatial scale at which they occur are largely unknown. We used an existing data set to evaluate the co‐occurrence patterns (i.e., random assemblages versus species co‐occurring more or less than expected at random) of three gar species in 62 dynamic river–floodplain habitats associated with the lower Mississippi River and its major tributaries. A novel parameterization of a multispecies occupancy model was utilized to examine the spatial relationships among the full array of possible gar assemblages across a gradient of floodplain habitats. Spotted Gar Lepisosteus oculatus were the most abundant and frequently encountered species (~78% of samples). Shortnose Gar L. platostomus (~27% of samples) and Longnose Gar L. osseus (~12% of samples) were relatively uncommon, and no Alligator Gar Atractosteus spatula were captured in over 600 electrofishing transects. Estimated detection probabilities of the encountered species varied (range = 0.27 [Longnose Gar] to 0.80 [Spotted Gar]), and five species‐specific environmental and sampling covariates predicted detection. Relatively strong co‐occurrence patterns between Shortnose Gar and Longnose Gar were significantly influenced by the proximity of a floodplain lake to a river (i.e., river : lake elevation change and linear distance) and by lake latitude. In contrast, the occurrence patterns of Spotted Gar were largely independent of the other species and had minor influences on the relationship between Longnose Gar and Shortnose Gar. We demonstrate how species co‐occurrence patterns can be leveraged to reduce uncertainty associated with species‐specific occupancy estimates and how species distribution models can be improved by utilizing abiotic and biotic features of the target ecosystems.

Effects of Temperature on Hatching Rate and Early Development of Alligator Gar and Spotted Gar in a Laboratory Setting

AbstractWater temperature influences both morphological and physiological development in fishes. However, the effects of water temperature on the early development of Alligator Gar Atractosteus spatula and Spotted Gar Lepisosteus oculatus are not well understood. Both gar species were collected from natural environments and spawned in a hatchery setting. After spawning, fertilized embryos were collected and transferred to the Oklahoma Fishery Research Laboratory, where the embryos (50–72 embryos/treatment) were placed into one of five water temperature treatments (15.5, 20.0, 23.8, 27.5, and 32.2°C) and observed over time to estimate the time to hatch and the time to reach the free‐swimming stage. Both species showed an inverse relationship between temperature and the timing of hatch and advancement to free‐swimming fingerlings for all treatments. In addition, Alligator Gar embryos did not develop at the coldest water temperature tested, and Alligator Gar juveniles held at the warmest temperature tested were observed with developmental abnormalities, potentially affecting their survival. The same temperature extremes had no comparable negative effect on Spotted Gar. The results of this study are useful for understanding early life history dynamics of these two species in their natural environments and can also be used by hatchery managers who are seeking to optimize their production protocols.

Hybridization and Population Genetics of Alligator Gar in Lake Texoma

AbstractThe Alligator Gar Atractosteus spatula (AG) is a long‐lived fish of growing management and conservation interest. Situated on the border of Texas and Oklahoma, Lake Texoma supports one of the last robust AG populations in Oklahoma; however, a genetic evaluation of this population is lacking. We genotyped AG individuals with 17 microsatellite loci, 7 of which also cross‐amplified in three sympatric Lepisosteus species: the Longnose Gar L. osseus (LN), Shortnose Gar L. platostomus (SN), and Spotted Gar L. oculatus (SP). Bayesian assignment analyses conducted in STRUCTURE and NewHybrids confirmed that a field‐identified hybrid was an F1 AG × LN and identified five other individuals that were suspected backcrosses (three LN × SN; two SN × SP). Alligator Gar had the lowest observed heterozygosity (0.179) and the lowest allelic richness (1.682) among the nonhybrid individuals of the four gar species examined. We also examined the potential for population structure and differences in pairwise relatedness (r) between two areas where AG are commonly encountered within Lake Texoma: the Red River and Washita River arms. No population structure was detected using noninformative or location priors in STRUCTURE, and estimates of r produced by the TrioML estimator in COANCESTRY were not significantly different between arms (overall mean r = 0.199). Point estimates of effective population size ranging from 16.3 to 29.2 suggested that the AG population may be vulnerable to the effects of inbreeding depression and random genetic drift. Results provide a genetic status assessment of AG in Lake Texoma and a baseline for future management and conservation decisions within Lake Texoma and surrounding regions.

Increased Probability and Efficiency of Gar Capture Using Multi- vs. Monofilament Gill Nets

Abstract Monofilament gill nets have increased in popularity in recent decades and are often considered to be superior to multifilament gill nets; however, this claim is still contested by many researchers. Target species, habitat characteristics, and mesh characteristics can all affect the efficacy and selectivity of these nets. Increased angling interest and declining home ranges have led to increased management efforts for gars (Lepisosteidae) among state and federal agencies. However, the sampling of gar species is notoriously difficult and has hindered subsequent management actions in some cases. This study aimed to compare probability and incidence rate of gar capture between net constructions (multi- vs. monofilament), net length (75 vs. 46 m length), sampling habitat (run vs. bend), and deployment orientation (parallel vs. perpendicular vs. diagonal in relation to river channel). We also assessed mode of capture investigate the effects of small mesh sizes (50.8 mm) on capture and potential retention of gars captured in gill nets. Results showed that the use of multifilament gill nets were three times more likely to capture at least one gar (1.3–6.3, 95% CI) than monofilament nets. Multifilament gill nets also averaged approximately twice as many gars per net than monofilament gill nets. Increasing water temperature also significantly increased the probability of gar capture, particularly above 15°C. In addition to mesh type and water temperature, habitat and gill net orientation also had significant effects on the incidence rate of gar capture. We primarily captured gars captured in the gill nets by entanglement (63%), which may have allowed for the wide range of length frequencies sampled in this study. Our study highlights the importance of considering multiple gill net constructions, deployments, and habitats when designing a research project or management plan for gar species. The use of multifilament gill nets can help resource managers to sample gar populations more effectively, resulting in better management strategies and practices.

Primer Designs for Identification and Environmental DNA (eDNA) Detection of Gars

AbstractGars (family Lepisosteidae) play important roles as apex predators in freshwater ecosystems, helping to balance fish populations. Several gar species are exploited as food and game fish, and some species are classified as vulnerable due to habitat loss. New molecular techniques to detect, monitor, and identify environmental DNA (eDNA) from gars might help inform management and conservation efforts for these interesting fish. The goal of this project was to develop and test PCR primers for gars, using specimens of all seven gar species, which are on exhibit at the Belle Isle Aquarium in Detroit, Michigan. Focusing on the mitochondrial gene for cytochrome oxidase I, we first designed primers to amplify DNA from all species of gars (“universal gar primers”) and confirmed their specificity in silico. These primers amplified DNA from all seven species, and species identities were confirmed by sequencing the PCR products. Only one of the three ostensibly Shortnose Gar Lepisosteus platostomus specimens sampled exhibited a Shortnose Gar matriline; two other specimens may be Longnose Gar L. osseus × Shortnose Gar hybrids. Genus‐targeted primers were developed that amplified all Atractosteus species and two of four Lepisosteus species. Species‐specific primers were developed for Longnose Gar, Shortnose Gar, and Tropical Gar Atractosteus tropicus. A primer set that targeted Alligator Gar A. spatula also amplified DNA from Cuban Gar A. tristocheus, but not other species. While the universal gar primers followed by sequencing confirmed the identities of all seven gar species at the Belle Isle Aquarium, PCR with the species‐specific primers enabled direct detection of the presence of DNA from the targeted species in the water in which those species had been maintained. Designing these primers is the first step in developing eDNA markers for gars, which in turn could inform the conservation and management of gar populations.

Skeletal development in the heterocercal caudal fin of spotted gar (lepisosteus oculatus) and other lepisosteiformes.

The caudal fin of actinopterygians experienced substantial morphological changes during evolution. In basal actinopterygians, the caudal fin skeleton supports an asymmetrical heterocercal caudal fin, while most teleosts have a symmetrical homocercal caudal fin. The transition from the ancestral heterocercal form to the derived homocercal caudal fin remains poorly understood. Few developmental studies provide an understanding of derived and ancestral characters among basal actinopterygians. To fill this gap, we examined the development of the caudal fin of spotted gar Lepisosteus oculatus, one of only eight living species of Holostei, the sister group to the teleosts. Our observations of animals from fertilization to more than a year old provide the most detailed description of the development of caudal fin skeletal elements in any Holostean species. We observed two different types of distal caudal radials replacing two transient plates of connective tissue, identifying two hypaxial ensembles separated by a space between hypurals 2 and 3. These features have not been described in any gar species, but can be observed in other gar species, and thus represent anatomical structures common to lepisosteiformes. The present work highlights the power and importance of ontogenic studies and provides bases for future evolutionary and morphological investigations on actinopterygians fins. Developmental Dynamics 247:724-740, 2018. © 2018 Wiley Periodicals, Inc.

Primer designs for identification and eDNA detection of gars (Lepisosteidae)

AbstractGars (family Lepisosteidae) serve important roles as apex predators in freshwater ecosystems., helping to balance fish populations. Several gar species are exploited as food and game fish, and some species are classified as vulnerable due to habitat loss. New molecular techniques to detect, monitor, and identify environmental DNA from gars might help inform management and conservation efforts for these interesting fish. Therefore the goal of this project was to develop and test PCR primers for gars, using specimens of all seven gar species, which are on exhibit at the Belle Isle Aquarium in Detroit, Michigan. Focusing on the mitochondrial gene for cytochrome oxidase I (COI), we first designed primers to amplify DNA from all species of gars (“universal gar primers”) and confirmed their specificity in silico. These primers amplified DNA from all seven species, and species identities were confirmed by sequencing the PCR products. Only one of three ostensible Shortnose Gar Lepisosteus platostomus spec...

Relative Growth by the Elongated Jaws of Gars: A Perspective on Polyphasic Loglinear Allometry.

Nonlinear regression was used to fit power functions with different forms for random error to data for length of the upper jaw versus length of the rest of body in two species of gars. Growth by the jaws of these species was reported earlier to conform to a pattern of polyphasic loglinear allometry indicative of relatively rapid growth by the jaw in small individuals (allometric exponent greater than 1) and relatively slow growth by the jaw in larger ones (allometric exponent less than 1). The new analyses revealed, however, that the pattern of relative growth by jaws of these fishes does not change with body size: the jaws grow more slowly than the rest of the body throughout life. The flaw in earlier investigations was the unrealistic assumption that data comprising a single sample in log domain form two (or more) statistically distinct distributions when expressed in arithmetic domain. The paradigm used in the current study provides a simple way to fit and compare different power functions, with different forms for random error, directly to raw data and thereby obviates the use of logarithmic transformations in allometric research.

Sexual Dimorphism in Alligator Gar

AbstractThe Alligator Gar Atractosteus spatula is currently imperiled due to habitat alterations and overharvest within much of this species’ range. Recent interest in improving management for this species within the USA and Mexico has spurred new creel restrictions, spawning area closures, and stocking programs, along with increased research on life history and population dynamics. These management and research measures can be improved by a noninvasive method for determining sex. Previous methods have required sacrificing the fish (for internal anatomy confirmation) or using costly and time‐consuming assays from a specialized laboratory. Evidence from other gar species suggests that sex determination is possible by examining sexually dimorphic external characters. We evaluated the utility of 13 morphological measurements for determining the sex of Alligator Gars of known gender (n = 117; SL range, 591–1,255 mm). Discriminate analysis identified two influential variables (snout length and caudal peduncle height) as sexually dimorphic. Univariate analyses identified three variables as sexually dimorphic (head length, snout length, and anal fin base length). Sexually dimorphic variables were used with SL to develop a method using serial body ratios (SL/snout length) followed by (snout length/anal fin base length) to identify sex in Alligator Gar to 93% accuracy in males and 72% accuracy in females.Received April 1, 2013; accepted June 3, 2013

Gene trees, species trees, and morphology converge on a similar phylogeny of living gars (Actinopterygii: Holostei: Lepisosteidae), an ancient clade of ray-finned fishes

Extant gars represent the remaining members of a formerly diverse assemblage of ancient ray-finned fishes and have been the subject of multiple phylogenetic analyses using morphological data. Here, we present the first hypothesis of phylogenetic relationships among living gar species based on molecular data, through the examination of gene tree heterogeneity and coalescent species tree analyses of a portion of one mitochondrial (COI) and seven nuclear (ENC1, myh6, plagl2, S7 ribosomal protein intron 1, sreb2, tbr1, and zic1) genes. Individual gene trees displayed varying degrees of resolution with regards to species-level relationships, and the gene trees inferred from COI and the S7 intron were the only two that were completely resolved. Coalescent species tree analyses of nuclear genes resulted in a well-resolved and strongly supported phylogenetic tree of living gar species, for which Bayesian posterior node support was further improved by the inclusion of the mitochondrial gene. Species-level relationships among gars inferred from our molecular data set were highly congruent with previously published morphological phylogenies, with the exception of the placement of two species, Lepisosteus osseus and L. platostomus. Re-examination of the character coding used by previous authors provided partial resolution of this topological discordance, resulting in broad concordance in the phylogenies inferred from individual genes, the coalescent species tree analysis, and morphology. The completely resolved phylogeny inferred from the molecular data set with strong Bayesian posterior support at all nodes provided insights into the potential for introgressive hybridization and patterns of allopatric speciation in the evolutionary history of living gars, as well as a solid foundation for future examinations of functional diversification and evolutionary stasis in a “living fossil” lineage.

Organometallic Chemistry of Ga+: Formation of an Unusual Gallium Dimer in the Coordination Sphere of Ruthenium

New insights into the distinct organometallic chemistry of the Ga(+) ion are presented. Ga(+) reacts as a strong electrophile with the electron rich ligand trismethylene-methane (C(CH(2))(3) (2-)) attached at Ru by insertion into a Ru--C bond. The resulting "gallamethylallyl" ligand behaves like strong nucleophile similar to known monovalent GaR species. This donor property leads to the dimeric structure of the product [{Ru(GaCp*)(3)[eta(3)-(CH(2))(2)C{CH(2)(mu-Ga)}]}(2)][(BAr(F))(2)] (4) (Cp*=C(5)Me(5), [BAr(F)]=[B{C(6)H(3)(CF(3))(2)}(4)]). Very unexpectedly, the two gallium ligands in this dimer are found in close vicinity to each other with a distance in the range of Ga--Ga bonds. Indeed, AIM calculations confirm a weak attractive closed shell Ga--Ga interaction. Finally, a novel example of a complex with substituent-free Ga(+) as a ligand was found in the compound [Ru(PCy(3))(2)(GaCp*)(2)(Ga)][BAr(F)] (6) (Cy=C(6)H(11), cyclohexyl), the very short Ru--Ga bond length confirming the assumption that Ga(+) represents a pure sigma/pi-accepting ligand in this case.

Gar biology and culture: status and prospects

Many lepisosteid populations in North America have declined and many are now threatened as a consequence of habitat loss and alteration and commercial and sport overfishing. Over the last two decades, morphological, histological and molecular studies allowed distinguishing between different phases of development and the nutritional condition of larvae. Ontogeny of the digestive enzymes of gar larvae indicated the possibility to feed them artificial feeds since early developmental stages. An in vitro digestibility system to test different feed ingredients has been used. Important characteristics of artificial diets were identified through different feeding experiments. Endocrinological studies showed the feasibility of altering larval development and the digestive capacity of larvae. Cloning of gar growth hormone opened new avenues to enhance growth in the gars. Plasmatic vitellogenin was isolated and purified, to develop a competitive enzyme-linked immunosorbent assay, which allowed the straightforward separation of males from females to establish appropriate proportions for reproduction and also was used to evaluate hormonal protocols to induce gonad recrudescence and spawning. This review analyzes the biology, ecology and physiology of different gar species as a basis for their domestication, mass production of larvae for repopulation experiments and for the culture of commercial-size gar.

Hybridization between Longnose and Alligator Gars in Captivity, with Comments on Possible Gar Hybridization in Nature

AbstractAlthough hybridization occurs widely in fishes, it has never been recorded in gars. Here, we describe the first known hybrids of the longnose gar Lepisosteus osseus and alligator gar Atractosteus spatula from four specimens spawned in an aquarium containing multiple gar species. Genetic analyses of cytochrome b and tyrosinase sequences and a microsatellite locus indicated that the four specimens were hybrid offspring of a female longnose gar and a male alligator gar. The combination of physical appearance, meristic counts, and mensural measurement ratios further discriminated the hybrids from each parent and supported the conclusion of hybrid origin. The four hybrids had body coloration and transverse scale rows similar to those of longnose gar, a snout length and shape intermediate between those of longnose and alligator gars, and two rows of teeth on the upper jaw as are seen in alligator gar. This conclusive evidence of intergeneric hybridization in the gars may provide insights into phylogenetic relationships in Lepisosteidae and hybridization theory and may explain unsubstantiated reports of gar hybridization in nature and the pet trade.

Associations between hydrological connectivity and resource partitioning among sympatric gar species (Lepisosteidae) in a Texas river and associated oxbows

Abstract – The middle Brazos River, located in east‐central Texas, is a meandering lowland river with many oxbow lakes on its flood plain. Flood dynamics of the Brazos River are aseasonal, and faunal exchange during lateral connections of the main river channel and oxbows is pulse‐like and occurs only during floods that may be months or years apart. Patterns of resource use among sympatric gar species (Lepisosteus oculatus, Lepisosteus osseus and Atractosteus spatula) associated with river–flood plain connectivity were studied for a period of 2 years (May 2003 to May 2005). The first year was relatively dry yielding few lateral connections, whereas the second year was relatively wet resulting in more frequent lateral connections. This study focused on habitat and diet partitioning among the three gar species in oxbow habitats with different connection frequencies and an active river channel site. Overall, 684 gars were collected with experimental gillnets: 19 A. spatula (alligator gar), 374 L. oculatus (spotted gar) and 291 L. osseus (longnose gar). There was strong partitioning of habitat between spotted and longnose gars, in which 98% of spotted gars were captured in oxbow habitats and 84% of longnose gars were captured in the river channel. Hydrology did not appear to affect habitat partitioning, although longnose gar abundance significantly increased in oxbows during the wet year. Diet overlap was high between spotted and longnose gars. Temporal variation in diet was significantly influenced by flood pulses that connected oxbows with the river channel, and which allowed predators and their prey to move between habitats.