Belonesox Research Articles

Comparative diets and prey resource competition between early-juvenile common snook Centropomus undecimalis and non-native pike killifish Belonesox belizanus.

Pike killifish Belonesox belizanusis an established non-native fish species in Florida, USA, that was first documented in south Florida in 1957 and then in Tampa Bay tributaries in 1994. Decreases in small-bodied fish abundances have been linked to the introduction of B. belizanus in both of these regions. Increases in the range and abundance of B. belizanusin the Tampa Bay area and overlap in habitat usage have led to concerns about potential competition with, and predation on, early-juvenile common snook Centropomus undecimalis [≤100 mm standard length (SL)]. Stomach contents of B. belizanus (N = 422; 14-127 mm SL) and early-juvenile C. undecimalis (N = 1132; 5-119 mm SL) were collected to examine the dietary overlap of these two species and potential differences in the diet of early-juvenile C. undecimalis from locations with and without B. belizanus co-occurring. Prey resources were collected by seine to assess prey resource limitation and prey selectivity. Stomach content analysis indicated that there was low overlap in the diet of early-juvenile C. undecimalis and B. belizanus (C ≤ 0.40). Early-juvenile C. undecimalis had a wider diet breadth, consuming many organisms that are not consumed by B. belizanus and which make up a large portion of the early-juvenile C. undecimalis diet. Analysis of prey resources indicated that some prey groups may have lower abundances in locations where B. belizanus are present, with some of these differences reflected in the diet of early-juvenile C. undecimalis. Despite these differences, there was minimal difference in the diet overlap of early-juvenile C. undecimalis from locations with and without B. belizanus co-occurring. Currently B. belizanus appear to be competing minimally with early-juvenile C. undecimalis for prey resources, with no substantial impacts being detected.

Northward expansion leads to cold tolerance? Investigating thermal adaptation of the non-native pike killifish (Belonesox belizanus) in Florida

For an introduced species to expand its range, individuals must be able to adapt to novel stressors (biotic and abiotic) that they may encounter. Florida has a distinct temperature gradient and rapid climate zone transitions from warmer subtropical regions to cooler temperate regions. Mean minimum temperatures are thought to prohibit northward movement of introduced fish species in south Florida. As the introduced Belonesox belizanus (pike killifish) expands its introduced range northward, it may be gaining cold tolerance. This study sought to compare thermal tolerances and cessation of feeding between adult B. belizanus from southern (initial, introduced population) and northern (spreading, fringe edge population) populations from its introduced range. To compare thermal tolerances between locations, southern individuals and northern individuals were acclimated to three temperatures (20, 25, and 30 °C) and their upper and lower lethal temperatures and cessation of feeding temperatures were measured. Two-way ANOVAs revealed that lower lethal temperatures and cessation of feeding temperatures were significantly different between northern and southern populations, with northern individuals having a lower lethal temperature approximately 0.5 °C lower and a cessation of feeding temperature approximately 2 °C lower compared with southern individuals. Directional selection may be influencing this non-native species’ thermal tolerance and feeding ability benefitting their continued effort to disperse from subtropical to temperate environments within Florida. This study indicates that B. belizanus may be gaining cold tolerance as it continues to spread northward in its introduced range.

Nonnative Pike Killifish Do Not Exert Predatory Pressure on Juvenile Common Snook

AbstractThe Pike Killifish Belonesox belizanus is an established nonnative fish species that was first documented in south Florida, USA, in 1957 and secondarily in Tampa Bay tidal tributaries in 1994. Decreased abundance and altered size structure in small‐bodied fish populations have been linked to Pike Killifish introductions in both of these regions. Increases in the range and abundance of Pike Killifish in Tampa Bay waters and overlap in habitat usage with juvenile Common Snook Centropomus undecimalis have led to concerns about potential predation on early juvenile (≤125 mm TL) Common Snook. We investigated predation of Pike Killifish on early juvenile Common Snook through experimental predation trials and stomach content analysis of Pike Killifish from field sampling. During predation trials, fasted, large adult (≥104 mm TL) Pike Killifish were presented with one of three prey taxa: Common Snook (N = 139), Pike Killifish conspecifics (N = 68), and Eastern Mosquitofish Gambusia holbrooki (N = 68); the fate of the prey was recorded after 48 h. Common Snook with both intact (N = 70) and clipped (N = 69) anal spines were used as prey to investigate whether this structure deterred predation by Pike Killifish. Predation trials indicated that Pike Killifish were capable of consuming early juvenile Common Snook up to 60 mm TL and that the anal spine did not deter predation by Pike Killifish. Stomach content analysis was performed on 422 wild‐caught Pike Killifish from Tampa Bay tidal tributaries where early juvenile Common Snook co‐occurred, but no Common Snook remains were found in their diets. Combined, these studies indicate that despite being able to consume relatively large early juvenile Common Snook, Pike Killifish do not exert predatory pressure on early juvenile Common Snook in the wild and therefore do not appear to be a factor contributing to population‐level effects or delayed recovery in Common Snook populations.

Distribution, Spread, and Habitat Predictability of a Small, Invasive, Piscivorous Fish in an Important Estuarine Fish Nursery

Invasive species often cause negative ecological and economic effects. Florida has >20 established invasive fish species but only seven exist in saltwater. The present study examined Belonesox belizanus (Pike Killifish), a Central American euryhaline fish introduced to Tampa Bay (west-central Florida) in the early 1990s, which has quantifiably reduced populations of small-bodied native fishes and may compete with prized sportfish juveniles in estuarine nursery habitat. Long-term monitoring revealed that B. belizanus occurs in estuarine waterbodies along a 31-km stretch of the bay’s eastern fringe, with a second, smaller population in two western tributaries. Spread rate was estimated to be 5.5–13 km year−1, intermediate among invasive poeciliids. A novel implementation of boosted regression tree modeling to assess B. belizanus habitat predictability found greater probability of presence with decreasing water depth and pH, whereas presence tended to be greatest at polyhaline salinity. It is hypothesized that B. belizanus distribution in Tampa Bay is constrained by deep, seawall habitats acting as ecological barriers. Further B. belizanus spread therefore may be most likely to occur by human release (from aquaria or bait buckets) or bird carry-off. Newly restored tidal habitat within the current range probably will be invaded quite quickly by B. belizanus.

Modeling the Relationship between Environmental Temperature and Feeding Performance in Florida (USA) Nonnative Fishes, with Implications for Invasive-Species Response to Climate Change

Aims: To determine the effect of environmental temperature on the feeding kinematics of two Florida (USA) invasive-fish species, pike killifish Belonesox belizanus and Mayan cichlid Cichlasoma urophthalmus, in an attempt to explore the adaptive response of wholeorganism performance to climate change. Study Design: Model I (Fixed-Effects Model) Linear Regression Analysis, y-Dependent Variable = Kinematics; x-Independent Variable = Environmental Temperature. Place and Duration of Study: Fish Ecophysiology Laboratory, Department of Biological Sciences, Florida Institute of Technology in May-December, 2011. Methodology: Four each of B. belizanus and C. urophthalmus, collected from invasive populations in Florida were acclimated in 38 liter experimental aquarium, trained, and filmed using high-speed video while eating fish-prey at 20°C, 25°C and 30°C. Four films per invasive-fish species at each temperature were analyzed using MaxTRAQ digitizing software. In each film, three kinematic-excursion (peak gape, peak hyoid depression and cranial elevation at peak gape) and three kinematic-timing (time to peak gape, hyoid depression, and cranial elevation) variables were measured. Each kinematic variable was regressed against temperature to model the relationship between feeding performance and Research Article Annual Research & Review in Biology, 4(1): 121-132, 2014 122 environmental temperature. Results: All experimental fishes behaved normally and fed aggressively in each of the three experimental temperature regimes. It is evident in the feeding kinematics-temperature plots that fish-feeding at each temperature was variable and unpredictable. Out of the 12 regression equations generated to model the relationship between feeding kinematics and environmental temperature, only one (peak gape in C. urophthalmus) showed a significant slope (Peak Gape = 1.42 + 0.01 Temperature; R = 0.22; P< 0.01). Conclusion: The models defining the relationship between feeding kinematics and environmental temperature are weak, as indicated by the extremely low values of the coefficient of determination (R). Empirical evidence indicates that the feeding performance of invasive B. belizanus and C. urophthalmus is not affected by temperature.

Scale-stacking in the live-bearer Belonesox belizanus (Poeciliidae)

An incidence of scale-stacking was found in a museum collection of Belonesox belizanus (Poeciliidae) from the Río Tesechocán, Veracruz, México. This phenomenon is thought to be unique to lepidophagous East African cichlids, although no studies have addressed the behaviour in any detail. This finding in B. belizanus, the first in Cyprinodontiformes, indicates Belonesox is able to manipulate scales into stacks in the buccal cavity.

Cryptic diversity in a widespread live-bearing fish (Poeciliidae:Belonesox)

Belonesox belizanus Kner (Teleostei: Poeciliidae) is a wide-spread livebearing species that occurs on the Atlantic Slope of Central America from southern Mexico to northern Costa Rica. Previous work has noted morphological variation within the species, and recognized two subspecies: Belonesox belizanus belizanus and Belonesox belizanus maxillosus. We used 1122 bp of cytochrome b and 617 bp of S7-1 DNA to conduct a phylogeographical study of Belonesox, aiming to examine the genetic distinctiveness of these taxa and other populations of Belonesox throughout the range. Bayesian phylogenetic and haplotype analyses indicated that B. b. maxillosus is not distinctive from other northern populations of Belonesox. However, a distinct phylogeographical break is evident near the Rio Grande in southern Belize. One clade comprises the putative B. b. maxillosus and all populations sampled north of the Rio Grande. The other clade comprises the Rio Grande and all populations south thereof. Fossil-calibrated divergence time estimates suggest that isolation of the northern and southern lineages of Belonesox occurred approximately 14.1 Mya. The phylogeographical structure recovered in the present study is interesting, considering that relatively few studies have examined molecular variation across this portion of Middle America in a time-calibrated framework. Furthermore, the present study suggests that more work is needed to adequately understand the factors that have shaped diversity of this region. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 848–860.

Dietary flexibility despite behavioral stereotypy contributes to successful invasion of the pike killifish, Belonesox belizanus, in Florida, USA

It is well known that the establishment of invasive-fish populations depends on the ability of introduced individuals to adapt to environmental conditions in the invaded ecosystem, including the ability to feed on diverse, locally available prey resources. Furthermore, the current invasive-biology paradigm postulates that having a generalist-food habit is key to the successful invasion of a novel community by exotic species. This study investigated how the invasive pike killifish, Belonesox belizanus, has succeeded in establishing exotic populations in Florida, USA despite having a feeding apparatus that is characteristic of a specialized piscivore (i.e., fish-eating fish). Pike killifish collected from their point of introduction in south Florida were (1) filmed using high speed video while feeding on live fishand shrimp-prey to determine whether prey type affects prey-capture kinematics and then (2) subjected to a prey-selectivity experiment to determine which prey type (live fish or shrimp) the invasive pike killifish eats when both prey are available in the environment. Results indicated that (1) prey-capture kinematics were not affected by prey type, indicating that consumption of fish and shrimp prey was accomplished using a stereotypical feeding repertoire, and (2) pike killifish consumed fish and shrimp when both prey were available in the feeding environment. It is concluded that the invasive pike killifish has the ability to feed on alternative, locally available prey using its piscivorous feeding functional morphology and prey-capture kinematics. This study contributes a new perspective to our understanding of the mechanisms that underlie success of exotic fishes in invaded communities. That is, the ability of a functional-morphological specialist to utilize stereotypical prey-capture kinematics (= behavior) in consuming alternative, locally available prey types (= dietary flexibility) contributes to the establishment of invasive populations. It is evident that these functional specialists are not constrained in their diet, thus, enabling them dietary flexibility and enhancing their invasive potential.

Invariant Feeding Kinematics of Two Trophically Distinct Nonnative Florida Fishes, Belonesox belizanus and Cichlasoma urophthalmus across Environmental Temperature Regimes

Nonnative fishes have the ability to adapt to environmental conditions in the invaded ecosystem and utilize resources that may have been absent in their native ecosystem. Belonesox belizanus and Cichlasoma urophthalmus are both nonnative fishes in Florida. Ecomorphological studies conclude that C. urophthalmus is a trophic generalist while B . belizanus is a trophic specialist. The current Florida distribution of these species indicates that C. urophthalmus spreads northerly into the colder regions of Florida at a faster rate than B . belizanus . Is it conceivable that this variation in rate of spread is due to differences in temperature response between these ecomorphologically distinct nonnative fishes? This study was designed to test the hypothesis that the prey-capture kinematics and behavior differ between C. urophthalmus and B . belizanus at a given temperature and across temperatures. Two-Way Repeated Measures Multivariate Analysis of Covariance (MANCOVAR) revealed that (1) at a given temperature, excursion and timing variables differed between species and (2) the kinematics of prey-capture did not vary across temperatures in both species. This interspecific comparison suggests that both species have the same temperature tolerance and that any difference in their rate of spread across Florida may be driven by factors other than species-specific physiological tolerance to temperature.

Thermal tolerance of the invasive Belonesox belizanus, pike killifish, throughout ontogeny.

The goal of this study was to characterize the variability of thermal tolerances between life-history stages of the invasive Belonesox belizanus and attempt to describe the most likely stage of dispersal across south Florida. In the laboratory, individuals were acclimated to three temperatures (20, 25, or 30°C). Upper and lower lethal thermal limits and temperatures at which feeding ceased were measured for neonates, juveniles, and adults. Thermal tolerance polygons were developed to represent the thermal tolerance range of each life-history stage. Results indicated that across acclimation temperatures upper lethal thermal limits were similar for all three stages (38°C). However, minimum lethal thermal limits were significantly different at the 30°C acclimation temperature, where juveniles (9°C) had an approximately 2.0°C and 4.0°C lower minimum lethal thermal limit compared with adults and neonates, respectively. According to thermal tolerance polygons, juveniles had an average tolerance polygonal area almost 20°C(2) larger than adults, indicating the greatest thermal tolerance of the three life-history stages. Variation in cessation of feeding temperatures indicated no significant difference between juveniles and adults. Overall, results of this study imply that juvenile B. belizanus may be equipped with the physiological flexibility to exercise habitat choice and reduce potential intraspecific competition with adults for limited food resources. Given its continued dispersal, the minimum thermal limit of juveniles may aid in continued dispersal of this species, especially during average winter temperatures throughout Florida where juveniles could act to preserve remnant populations until seasonal temperatures increase.

Assessing Effects of the Nonindigenous Pike Killifish on Indigenous Fishes in Tampa Bay, Florida, Using a Weighted‐Evidence Approach

AbstractNonindigenous fish introductions may result in significant negative ecological and economic effects. Pike killifish Belonesox belizanus, a small‐bodied piscivorous fish native to Central America, was introduced into South Florida in 1957 and raised concerns because of its consumption of small‐bodied fishes. The present study examined the negative effects on indigenous fishes from a second pike killifish population that invaded Tampa Bay several decades later. Four data sets were used to test several hypotheses based on earlier observations from South Florida: potential indigenous prey fish populations are less abundant or less frequently occurring or have a larger size composition (1) in invaded water bodies than in uninvaded water bodies and (2) following invasion than before invasion (with no concurrent change in uninvaded systems). For each prey species, the result of each hypothesis test was scored (2 = accept, 1 = tentatively accept, and 0 = reject) and the average score of all hypotheses was calculated, weighted by the relative rankings of the factors influencing the scope of inference from each data set (e.g., number of samples, years, and water bodies). Three resident (nonmigratory or potamodromous) small‐bodied species (sailfin molly Poecilia latipinna, eastern mosquitofish Gambusia holbrooki, and sheepshead minnow Cyprinodon variegatus) showed the most evidence of potential effects and had overall weighted‐evidence scores of around 50% (i.e., as much evidence for pike killifish effects as against). There was much greater evidence of effects of pike killifish when calculating scores based only on the abundance and frequency‐of‐occurrence hypotheses because the three species were two to six times less abundant or frequently occurring in the presence of, or after invasion by, pike killifish. Migratory species showed little evidence of negative effects, probably because they recruit from larger source populations and are not year‐round residents of pike killifish habitat.

Environmental correlates of the abundance and distribution of Belonesox belizanus in a novel environment

Environmental factors, such as temperature, dissolved oxygen, salinity, and pH may influence the population dynamics of an introduced species by imposing limits to its distribution and abundance. In 1957, the non-indigenous pike killifish, Belonesox belizanus Kner, was released into a Miami-Dade County, Florida, canal, from which it has since spread across most of south Florida. The main goal of this study was to characterize patterns of covariation between B. belizanus density and temporal, spatial, and physicochemical variables, and attempt to identify which physicochemical variables may explain variation in densities of this species. Results of AICc model selection indicated that patterns of physicochemical variables such as pH, salinity, and temperature correlated with annual change in B. belizanus density, and that these physicochemical- density patterns were mesohabitat specific. For the southern most sites, the interaction between tem- perature and salinity provide the best model to explain B. belizanus density, whereas variability in pH provides the best model at northern sites. These patterns of covariance between density and specific physicochemical variables suggests that specific mesohabitat characteristics may play a role in mediating the physiological, behavioral, and/or ecological performance of this introduced species in Florida and elsewhere. Future studies will test hypotheses on the direct and indirect effects of these physicochemical variables within the context of specific mesohabitats on the behavior and physiology of B. belizanus in its novel environment in South Florida.

Distribution and Abundance of Introduced Fishes in Florida's Charlotte Harbor Estuary

A growing number of non-native fishes have been introduced into Florida waters in recent years, yet little information has been available on their distribution and abundance in southwest Florida. The ichthyofauna of the Charlotte Harbor estuary, Florida, was intensively sampled from 1989 through 2007. We collected eight introduced fish taxa: African jewelfish (Hemichromis letourneuxi), blue tilapia (Oreochromis aureus), brown hoplo (Hoplosternum littorale), grass carp (Ctenopharyngodon idella), Mayan cichlid (Cichlasoma urophthalmus), sailfin catfishes (Pterygoplichthys spp.), spotted tilapia (Tilapia mariae), and walking catfish (Clarias batrachus). These fishes were found principally in tidal rivers, especially the Caloosahatchee River. Other introduced species, such as Asian swamp eel (Monopterus albus), blackchin tilapia (Sarotherodon melanotheron), and pike killifish (Belonesox belizanus), are known to occur in neighboring bay systems but have yet to be reported in the Charlotte Harbor estuary. Continued monitoring will help us detect additional species that are introduced to the estuary, expansions in the ranges of documented species, and assemblage-level changes.

Unusual kinematics and jaw morphology associated with piscivory in the poeciliid, Belonesox belizanus

Piscivory in fishes is often associated with the evolution of highly elongate jaws that achieve a large mouth opening, or gape. Belonesox belizanus, the pike killifish, has independently evolved this morphology, which is derived from short-jawed poeciliids within the Cyprinodontiformes. Using kinematic analysis of high-speed video footage, we observed a novel aspect of the elongate jaws of Belonesox; the premaxilla rotates dorsally during mouth opening, while the lower jaw rotates ventrally. Anatomical study revealed that this unusual motion is facilitated by the architecture of the premaxillomandibular ligament, prominent within cyprinodontiforms. In Belonesox, it allows force to be transferred from the lower jaw directly to the premaxilla, thereby causing it to rotate dorsally. This dorsal rotation of the premaxilla appears to be assisted by a mediolateral twisting of the maxilla during jaw opening. Twisting maxillae are found in members of the group such as Fundulus, but are lost in Gambusia. Models revealed that elongate jaws partially account for the enlarged gape, but enhanced rotation at the quadrato-mandibular joint was equally important. The large gape is therefore created by: (i) the convergent evolution of elongate jaws; (ii) enhanced jaw rotation, facilitated by loss of a characteristic cyprinodontiform trait, the lip membrane; and (iii) premaxilla rotation in a novel direction, facilitated by the retention and co-option of additional cyprinodontiform traits, the premaxillomandibular ligament and a twisting maxilla.

Differences in reproductive seasonality of the Central American cichlidCichlasoma urophthalmusfrom three ‘cenotes’ (sinkholes)

Summary A total of 966 cichlids, Cichlasoma urophthalmus, was sampled from three karstic water bodies (cenotes) in the Yucatan Peninsula. Sex ratio was not different from 1. Specimens with ripe eggs were found during the dry and rainy seasons in the inland cenote and during the dry, rainy, and north winds seasons in the two wetland cenotes. With respect to relative fecundity, data show the C. urophthalmus inland population as two- to three-fold greater (53.1 ± 27.7) than the wetland populations (15.7 ± 5.1 and 18.2 ± 3.1). This is attributable to the different breeding strategies of C. urophthalmus populations inhabiting these two types of cenotes. In particular, the ichthyofauna from the two wetlands showed not only higher species richness (17 and 16 species) but also a higher number of potential predators (nine and eight species) as compared to the inland cenote (six species; two potential predators). It is hypothesized that C. urophthalmus adjusts its clutch size and extends its breeding periods as a response to riskier sites as compared to more secure ones; a higher competition for breeding sites and to increased fishing mortality.

Salsuginus neotropicalis n. sp. (Monogenea: Ancyrocephalinae) from the pike killifish Belonesox belizanus (Atheriniformes: Poeciliidae) from southeastern Mexico.

Salsuginus neotropicalis n. sp. is described from the gills of Belonesox belizanus (Kner), the pike killifish (Poeciliidae), from the southeastern Mexico. S. neotropicalis is distinguished from all other congeners by the morphology of the haptoral sclerites, especially by the presence of a ventral bar with notably enlarged ends, and by possessing overlapping gonads. The diagnosis of Salsuginus is amended based on the position of gonads in this species. This is the first known Salsuginus species occurring in a freshwater fish from the Neotropical Region.

Exposure of great egret (Ardea albus) nestlings to mercury through diet in the everglades ecosystem

AbstractWe estimated exposure of great egret (Ardea albus) nestlings to mercury in food in the Florida Everglades, USA, by collecting regurgitated food samples during the 1993 to 1996 breeding seasons and during 1995 measured concentrations of mercury in individual prey items from those samples. Great egret nestlings had a diet composed predominantly of fish (&gt;95% of biomass), though the species composition of fish in the diet fluctuated considerably among years. Great egrets concentrated on the larger fish available in the marsh, especially members of the Centrarchidae. The importance of all nonnative fish fluctuated from 0 to 32% of the diet by biomass and was dominated by pike killifish (Belonesox belizanus) and cichlids (Cichlidae). Total mercury concentrations in prey fish ranged from 0.04 to 1.40 mg/kg wet weight, and we found a significant relationship between mass of individual fish and mercury concentration. We estimated the concentration of total mercury in the diet as a whole by weighting the mercury concentration in a given fish species by the proportion of that species in the diet. We estimate that total mercury concentrations in the diets ranged among years from 0.37 to 0.47 mg/kg fish (4‐year mean = 0.41 mg/kg). We estimated total mercury exposure in great egret nestlings by combining these mercury concentrations with measurements of food intake rate, as measured over the course of the nestling period in both lab and field situations. We estimate that, at the 0.41 mg/kg level, nestlings would ingest 4.32 mg total mercury during an 80‐day nestling period. Captive feeding studies reported elsewhere suggest that this level of exposure in the wild could be associated with reduced fledging mass, increased lethargy, decreased appetite, and, possibly, poor health and juvenile survival.

Male body size and male‐male competition: Interspecific variation in poeciliid fishes

Abstract Poeciliidae are a family of viviparous fishes characterized by reversed sexual size dimorphism. Although in all species males are smaller than females, there is a large variability in size dimorphism both between and within species. It has been suggested that variation in the degree of sexual size dimorphism across the family is related to differences in intensity and direction of both intra‐ and intersexual selection. Here the relationship between male body size and in‐trasexual competition, and its effect on male mating success, have been studied in four poeciliid species. Wide interspecific variation was found in the intensity of male‐male competition and in the importance of body size to achieve dominance. In Belonesox belizanus and Girardinus falcatus, larger dominant males almost completely excluded other males from access to the females. Males of Phalloceros caudimaculatus are less aggressive and dominance influences their access to females to a lesser degree. In Heterandria formosa, aggre...

The fishes of northern and central Veracruz, Mexico

The northern and central part of Veracruz, Mexico, as herein delimited, is inhabited by 121 species of fish, in 83 genera and 47 families. Four species and 3 families are Nearctic, 28 species and 6 families are Neotropical, and 1 species is circumtropical. Ecologically, 8 species and 4 families are primary, 25 species and 6 families are secondary, 30 families are peripheral, and 7 families are marine, many of them marine accidentals. A mountainous area near Punta del Morro almost reaches the sea, and acts as a filter for primary and secondary species. Its importance had not been described in detail. From the north, the following species range to Punta del Morro or less:astyanax mexicanus, Dionda ipni, Ictalurus cf.furcatus, I. cf.punctatus, Lucania parva, Cyprinodon variegatus, Gambusia affinis, G. vittata, Heterandria sp.,Poecilia formosa, P. latipinna, Xiphophorus birchmani, X. variatus, Cichlasoma cyanoguttatum, C. labridens andC. sp.. From the south, the species that approach or reach Punta del Morro are:Astyanax aeneus, Hyphessobrycon compressus, Rhamdia guatemalensis, R. laticauda, Rivulus cf.robustus, Belonesox belizanus, Poeciliopsis gracilis, Xiphophorus andersi, X. maculatus, andOphisternon aenigmaticum. Eight species including one peripheral are present on both sides and constitute short penetrations across the barrier. At least nine species represent introductions, purposeful or accidental.

Population structure, reproduction and laboratory behavior of the introduced Belonesox belizanus (Poeciliidae) in Florida

The pike killifish, Belonesox belizanus, is native to Mexico and Central America and was introduced into Dade County, Florida in 1957. This study reports on the structure and reproduction of the Florida population and compares the species with other members of the family Poeciliidae. The mean standard length (SL) of mature females was about 103 mm. Most females larger than 75 mm SL contained yolked ova, fertilized eggs, or embryos. Mature males averaged about 72 mm SL, and most males larger than 55 mm SL were mature. The sex ratio was significantly skewed in favor of females among adults, but it did not differ significantly from 1:1 among immature fish. Average brood size was about 99, and there was a significant positive correlation of brood size with size of the parent female. There was no evidence of superfetation. Sizes and weights of embryos and neonates were the largest reported for the family. There was a significant decrease in mean embryo weight as development proceeded, indicating that developing embryos received little or no nutrient input from the maternal system after fertilization. The average interbrood interval of aquarium-held females was 42 days, and females stored viable sperm at least 47 days. Reproduction continued year round in the field. Laboratory-born neonates were immediately piscivorous and exhibited distinctive behavior associated with filling the swimbladder and with avoiding detection by predators.