Gulf Killifish Fundulus Grandis Research Articles

Live‐bait industry as a pathway for movement of nonnative and invasive species: Implications for conservation of native Texas fishes

AbstractObjectiveLive‐bait species are widely used in recreational fishing throughout the United States. However, the use of invasive fish species as live bait has been identified as a common pathway for their introduction into aquatic ecosystems. We assessed the role that the live‐bait industry has in facilitating the introduction of nonnative and invasive species into Texas rivers. We focused on two invasive cyprinodontid species, the Sheepshead Minnow Cyprinodon variegatus and Gulf Killifish Fundulus grandis, which are believed to have been introduced into inland Texas rivers via bait‐bucket releases by anglers.MethodsWe conducted telephone and in‐person surveys of live‐bait shops in Texas on a seasonal basis (summer, fall, winter, spring) for 1 year. Locally owned bait shops and regional aquaculture facilities and hatcheries were included in the surveys.ResultSurveys did not reveal the presence of these invasive cyprinodontids in inland bait shops but did reveal the sale of nonnative Goldfish Carassius auratus and their black color morph, the black salty goldfish. Surveys conducted among inland and coastal live bait shops confirmed the sale of only one nonnative bait fish and six bait items native only to certain regions of Texas. Telephone surveys with aquaculture industry experts revealed that the aquaculture industry was also facilitating the movement of nonnative game and nongame fish species throughout the state.ConclusionGiven the potential for nonnative and invasive species to negatively affect recipient aquatic ecosystems, the continued distribution of such species within the aquaculture industry represents a potential threat in Texas. Our findings highlight the need for close monitoring of the live‐bait industry in the state to prevent further introductions into inland waters and reduce potential ecological risks to native fish populations and overall ecosystem functions and services.

Previous oil exposure alters Gulf Killifish Fundulus grandis oil avoidance behavior.

Oil spills threaten the structure and function of ecological communities. The Deepwater Horizon spill was predicted to have catastrophic consequences for nearshore fishes, but field studies indicate resilience in populations and communities. Previous research indicates many marsh fishes exhibit avoidance of oil contaminated areas, representing one potential mechanism for this resilience. Here, we test whether prior oil exposure of Gulf killifish Fundulus grandis alters this avoidance response. Using choice tests between unoiled and oiled sediments at one of three randomized concentrations (low: 0.1 L oil m−2, medium: 0.5 L oil m−2, or high: 3.0 L oil m−2), we found that, even at low prior exposure levels, killifish lose recognition of oiled sediments compared to control, unexposed fish. Preference for unoiled sediments was absent across all oil concentrations after oil exposure, and some evidence for preference of oiled sediments at high exposure was demonstrated. These results highlight the lack of response to toxic environments in exposed individuals, indicating altered behavior despite organism survival. Future research should document additional sublethal consequences that affect ecosystem and food web functioning.

Simultaneous estimation of dispersal and survival of the gulf killifish Fundulus grandis from a batch-tagging experiment

Simultaneous estimation of dispersal and survival of the gulf killifish Fundulus grandis from a batch-tagging experiment

Egg Production of Gulf Killifish Is Dependent on Broodstock Rearing Density but Not Spawning Substrate Surface Area

AbstractThe Gulf Killifish Fundulus grandis is a popular baitfish for recreational fisheries and is a candidate for commercial‐scale culture; however, its relatively low fecundity compared to other baitfish presents a production challenge. Egg output in relation to broodstock densities and spawning mat surface areas was evaluated in recirculating aquaculture systems (RASs). In experiment 1, broodstock were stocked at two densities (45 and 90 fish/m³), with eggs collected three times per week for 8 weeks. Broodstock (15–17 g) that were held at 45 fish/m³ had greater reproductive output (3.93 eggs·female−1·d−1) than broodstock that were held at 90 fish/m³ (2.22 eggs·female−1·d−1). However, there was no difference between the number of eggs per collection (1,005 and 1,107 eggs per 3,600‐L tank) or total egg production (23,202 and 25,802 eggs per 3,600‐L tank), indicating that reproductive output was limited by another factor, such as available spawning substrate. Therefore, in experiment 2, broodstock (12–16 g) were stocked at a density of 100 fish/m³ in all tanks and were held for 8 weeks with one of three spawning mat (Spawntex) surface areas: 4,500 cm2 (one tier), 9,000 cm2 (two tiers), or 13,500 cm2 (three tiers). Reproductive output was 2.12, 2.27, and 2.21 eggs·female−1·d−1 for the one‐tier, two‐tier, and three‐tier treatments, respectively, with no differences among treatments. There was also no among‐treatment difference in the number of eggs per collection (1,724, 1,858, and 1,794 eggs/tank) or in the total number of eggs collected (27,587, 29,728, and 28,704 eggs/tank), suggesting that increasing the surface area of spawning material does not increase egg production. Therefore, a stocking density of 45 fish/m³ and a spawning mat surface area of 4,500 cm2 in commercial‐scale RAS broodstock tanks result in similar egg production compared to a higher stocking density and greater spawning mat surface area.

Effects of passive integrated transponder tagging on cortisol release, aerobic metabolism and growth of the Gulf killifish Fundulus grandis.

The effects of passive integrated transponder (PIT) tagging on cortisol release, standard metabolic rate (SMR) and daily specific growth rate (GS ) were evaluated in the Gulf killifish, Fundulus grandis, a small estuarine fish native to the Gulf of Mexico. Cortisol release by individual fish was measured non-invasively prior to PIT tagging, immediately after tagging and once per week for 1 month following tagging. Within the first 2 h of tagging, cortisol release rates were significantly elevated compared with values measured prior to tagging and significantly higher than that of fish handled identically except not implanted with PIT tags. By 1 week after PIT tagging, cortisol release rates returned to control levels. SMR, determined by intermittent-flow respirometry and GS , defined as per cent change in body mass per day, were measured prior to PIT tagging and weekly for 1 month after tagging. Neither SMR nor GS was significantly different in tagged v. untagged fish for the duration of the study. One month after tagging, haematocrit, plasma cortisol, blood glucose and blood lactate did not differ between tagged and untagged individuals. Therefore, after a transient stress response that subsides within 1 week, PIT tagging had no significant effects on these physiological variables in F. grandis, validating its use as a method of marking this and other small fishes.

Demonstration of Survival, Growth, and Reproduction of Gulf Killifish in Freshwater Ponds

AbstractThe Gulf Killifish Fundulus grandis, a popular baitfish species inhabiting estuaries in the northern Gulf of Mexico, has potential as an aquaculture species, particularly if it can be produced in low‐salinity or freshwater ponds. Because growth and survival in freshwater ponds are not known, two size‐classes were examined over a 16‐week period. Initial mean stocking weights and densities were 0.47 g/fish and 26,500 fish/ha for the smaller size‐group, which was stocked into three 0.04‐ha ponds, and 6.12 g/fish and 20,450 fish/ha for the larger size‐group, which was stocked into two 0.04‐ha ponds. Growth and survival were similar between size‐classes: mean final weight and mean survival were 7.88 g/fish and 54.3%, respectively, for the smaller size‐group, and 13.90 g/fish and 43.1% for the larger size‐group. Mean weight gain was very similar between size‐groups (small: 7.41 g; large: 7.78 g); steady growth was observed from June until mid‐September, whereas little growth and declines in condition factor were observed from mid‐September to mid‐October, corresponding with decreases in water temperature. Gulf Killifish were resilient to a wide range of water quality conditions in freshwater ponds and reached market sizes of 3 g at about 4 weeks and 5 g by 8 weeks.

Influence of euthanasia method on blood and gill variables in normoxic and hypoxic Gulf killifish Fundulus grandis.

In many experiments, euthanasia, or humane killing, of animals is necessary. Some methods of euthanasia cause death through cessation of respiratory or cardiovascular systems, causing oxygen levels of blood and tissues to drop. For experiments where the goal is to measure the effects of environmental low oxygen (hypoxia), the choice of euthanasia technique, therefore, may confound the results. This study examined the effects of four euthanasia methods commonly used in fish biology (overdose of MS-222, overdose of clove oil, rapid cooling and blunt trauma to the head) on variables known to be altered during hypoxia (haematocrit, plasma cortisol, blood lactate and blood glucose) or reflecting gill damage (trypan blue exclusion) and energetic status (ATP, ADP and ATP:ADP) in Gulf killifish Fundulus grandis after 24 h exposure to well-aerated conditions (normoxia, 7·93 mg O2 l-1 , c. 150 mm Hg or c. 20 kPa) or reduced oxygen levels (0·86 mg O2 l-1 , c. 17 mm Hg or c. 2·2 kPa). Regardless of oxygen treatment, fish euthanized by an overdose of MS-222 had higher haematocrit and lower gill ATP:ADP than fish euthanized by other methods. The effects of 24 h hypoxic exposure on these and other variables, however, were equivalent among methods of euthanasia (i.e. there were no significant interactions between euthanasia method and oxygen treatment). The choice of an appropriate euthanasia method, therefore, will depend upon the magnitude of the treatment effects (e.g. hypoxia) relative to potential artefacts caused by euthanasia on the variables of interest.

Avoidance of oil contaminated sediments by estuarine fishes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 576:125-134 (2017) - DOI: https://doi.org/10.3354/meps12084 Theme Section: Response of nearshore ecosystems to the Deepwater Horizon oil spill Avoidance of oil contaminated sediments by estuarine fishes Charles W. Martin* Department of Oceanography Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA Present address: University of Florida Institute of Food and Agricultural Sciences Nature Coast Biological Station, Cedar Key, FL 32625, USA *Corresponding author: martin.charles.w@gmail.comAdvance View was available online March 8, 2017; subsequently updated May 2, 2017 ABSTRACT: The explosion of the Deepwater Horizon drilling platform and subsequent discharge of hydrocarbons into the Gulf of Mexico is the largest oil spill that has affected US waters. To date, studies of ecological effects on coastal fishes have produced complex results. While laboratory studies indicate that oil has widespread, pervasive impacts on fish physiology, field assessments often document few impacts to fish abundance and biomass following a spill. The dichotomy of such results suggests that negative individual-level effects do not translate to population/community-level consequences. One explanation for this discrepancy is that mobile organisms may avoid oil, which was very patchily distributed. Here, I present the results of experiments using 3 estuarine fishes (gulf killifish Fundulus grandis, sailfin molly Poecilia latipinna, and sheepshead minnow Cyprinodon variegatus) to determine whether behavioral avoidance occurs at a range of concentrations (0, 10, 20, and 40 ml oil l-1 of sediment) and weathering (fresh or weathered oil) scenarios. All 3 species avoided medium (35, 18, 10% of trial time, respectively) and high concentrations of fresh oil (30, 20, and 15%, respectively), while time spent over contaminated sediments at low concentrations of fresh oil was higher (30, 40, and 40%, respectively). Weathered crude elicited no significant avoidance behavior, with fish occupying between 40 and 60% of the trial period over these sediments, regardless of concentration. This research highlights the heretofore unrecognized role of behavior in fish resilience, as well as the need for future studies to incorporate ecologically relevant weathering rates. Such results are critical to the successful management of motile resources, such as estuarine fishes, in response to anthropogenic disasters such as oil spills. KEY WORDS: Salt marsh · Gulf of Mexico · Fish ecology · Experiment · Avoidance behavior · Oil contamination · Oil spill · Deepwater Horizon · Macondo Full text in pdf format PreviousNextCite this article as: Martin CW (2017) Avoidance of oil contaminated sediments by estuarine fishes. Mar Ecol Prog Ser 576:125-134. https://doi.org/10.3354/meps12084 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 576. Online publication date: August 03, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Feeding Larval Gulf Killifish: Total Replacement of Artemia Nauplii and Co‐Feeding from Hatch

AbstractLarval Gulf Killifish Fundulus grandis hatching from air‐incubated eggs are precocial, with well‐developed mouths and eyes providing an immediate capacity for exogenous feeding. Live feeds are almost universally used in finfish and crustacean hatcheries, with newly hatched brine shrimp Artemia spp. nauplii being a standard. Across two experiments from hatch in Gulf Killifish, we evaluated the ability to replace Artemia nauplii with prepared diets. Experiment 1 measured growth and survival from hatch through 8 weeks in larval Gulf Killifish fed either Artemia nauplii or one of five commercially available diets. Experiment 2 measured survival and SL of Gulf Killifish larvae at 5, 10, and 15 d posthatch among treatments consisting of animals fed Artemia nauplii, the best‐performing commercial diet from experiment 1, or an experimental microbound diet or “co‐fed” the microbound diet and Artemia. In experiment 1, Gulf Killifish larvae fed live Artemia nauplii exhibited growth that significantly outperformed commercially available formulated diets. Mean ± SE (SEM) survival (%) among treatments ranged from 51.1 ± 7.4 to 86.2 ± 2.1. Larvae fed one commercially prepared diet outperformed larvae fed the other four commercial diets in terms of growth. In experiment 2, mean SL was significantly different among treatments by 15 d posthatch. Mean ± SEM survival (%) across all treatments in experiment 2 ranged from 87.7 ± 0.8 to 99.2 ± 0.4. Results of these experiments are some of the first to document acceptable growth and survival of finfish larvae when Artemia nauplii are completely replaced with formulated diets from hatch. The distinctive larval biology of the study species in concert with the ability to air‐incubate the embryos were presumably important factors in the ability to completely replace Artemia nauplii from hatch.

Freshwater influences on embryos, hatching and larval survival of euryhaline Gulf killifish Fundulus grandis and potential constraints on habitat distribution.

The influence of fresh water on potential habitat occupancy of early life-history stages of euryhaline Gulf killifish Fundulus grandis was determined by evaluating fertilization of freshwater-spawned eggs and subsequent survival of embryos and larvae in comparison with saline water (salinity 7). Overall per cent fertilization of eggs was low (mean ± s.e. = 20·21 ± 0·03%). Embryo survival was greater in saline water, but hatching rate (mean ± s.e. = 81·6 ± 0·1%) and post-hatch survival of larvae in fresh water (mean ± s.e. = 74·5 ± 0·1%) was relatively high. Therefore, the relative limitation of fresh water on habitat distribution of F. grandis changes with development, stimulating further questions on factors that may constrain habitat distribution of euryhaline fishes.

Effects of Low Salinities on Osmoregulation, Growth, and Survival of Juvenile Gulf Killifish

AbstractThe Gulf Killifish Fundulus grandis, a popular baitfish, is a euryhaline fish species native to coastal estuaries of the Gulf of Mexico and the eastern coast of Florida. Established culture methods have relied on a saline water source but such methods have not been widely adapted by the commercial sector. Since this species is highly euryhaline, there is potential for freshwater culture via the utilization of established inland facilities. In order to assess the feasibility of inland culture, changes in Gulf Killifish hypo‐osmotic tolerance throughout early growth were evaluated. Gulf Killifish were challenged with low salinity treatments of 0 (freshwater), 2.5, 5.0, and 7.5‰ at 2, 7, and 12 weeks posthatch for 4 weeks to determine growth, survival, gill Na+,K+‐ATPase activity, and whole‐body Na+ content. Gill Na+,K+‐ATPase activity and whole‐body ion samples were collected at 0, 2, 14, and 28 d posttransfer (dpt) for each age‐group. Results indicated Gulf Killifish at 2 weeks posthatch grew and survived at 2.5‰ as well as at higher salinities, but growth was reduced in freshwater. At 7 and 12 weeks posthatch, freshwater survival and growth rates at 0‰ salinity were comparable with other salinity treatments. Gill Na+,K+‐ATPase activity increased in Gulf Killifish that were transferred to freshwater at both 7 and 12 weeks posthatch. Whole‐body Na+ content was higher in freshwater 28 dpt in the 2‐week‐posthatch age‐group, and 14 dpt in the 7‐week‐posthatch age‐group. There were few differences in Na+,K+‐ATPase activity and whole‐body Na+ content between salinity treatments in the 12‐week‐posthatch age‐group. These results suggest Gulf Killifish develop hypo‐osmotic tolerance at less than 2 weeks of age posthatch and culture in low salinities including freshwater will be more successful with fish older than 7 weeks of age.

Characterization of Isolates of Streptococcus agalactiae from Diseased Farmed and Wild Marine Fish from the U.S. Gulf Coast, Latin America, and Thailand.

We examined Lancefield serogroup B Streptococcus isolates recovered from diseased, cultured hybrid Striped Bass (Striped Bass Morone saxatilis × White Bass M. chrysops) and wild and cultured Gulf Killifish Fundulus grandis from coastal waters of the U.S. Gulf of Mexico (Gulf coast) and compared those isolates to strains from tilapias Oreochromis spp. reared in Mississippi, Thailand, Ecuador, and Honduras and to the original Gulf coast strain identified by Plumb et al. ( 1974 ). The isolates were subjected to phylogenetic, biochemical, and antibiotic susceptibility analyses. Genetic analysis was performed using partial sequence comparison of (1) the 16S ribosomal RNA (rRNA) gene; (2) the sipA gene, which encodes a surface immunogenic protein; (3) the cspA gene, which encodes a cell surface-associated protein; and (4) the secY gene, which encodes components of a general protein secretion pathway. Phylogenies inferred from sipA, secY, and cspA gene sequence comparisons were more discriminating than that inferred from the 16S rRNA gene sequence comparison. The U.S. Gulf coast strains showed a high degree of similarity to strains from South America and Central America and belonged to a unique group that can be distinguished from other group B streptococci. In agreement with the molecular findings, biochemical and antimicrobial resistance analyses demonstrated that the isolates recovered from the U.S. Gulf coast and Latin America were more similar to each other than to isolates from Thailand. Three laboratory challenge methods for inducing streptococcosis in Gulf Killifish were evaluated-intraperitoneal (IP) injection, immersion (IMM), and immersion plus abrasion (IMMA)-using serial dilutions of S. agalactiae isolate LADL 97-151, a representative U.S. Gulf coast strain. The dose that was lethal to 50% of test fish by 14 d postchallenge was approximately 2 CFU/fish via IP injection. In contrast, the fish that were challenged via IMM or IMMA presented cumulative mortality less than 40% by 14 d postchallenge.

Physiological management of dietary deficiency in n-3 fatty acids by spawning Gulf killifish (Fundulus grandis)

Lipid dynamics of spawning fish are critical to the production of viable embryos and larvae. The present study utilized manipulation of dietary fatty acid (FA) profiles to examine the ability of spawning Gulf killifish (Fundulus grandis) to mobilize critical lipid components from somatic reserves or synthesize long-chain polyunsaturated FAs (LC-PUFAs) de novo from shorter-chain C18 precursors. An egg and multi-tissue evaluation of changes in FA concentrations across time after fish were switched from LC-PUFA-rich to LC-PUFA-deficient experimental diets was employed. The two experimental diets contained lipid sources which differed drastically in n-3 C18 FA content but had similar levels of n-6 C18 FAs. Discrete effects of dietary n-3 FAs can be analyzed because n-3 and n-6 represent distinct metabolic families which cannot be exchanged in vivo. Results indicate that a combination of mobilization and de novo synthesis is likely utilized to maintain physiologically required FA levels in critical tissues and embryos. Mobilization was supported by decreases in LC-PUFAs in somatic tissues and decreases in intraperitoneal fat content and liver mass. Evidence for biosynthesis was provided by a higher level of n-3 LC-PUFAs in the liver and ova of fish fed diets containing n-3 C18 precursors versus those fed diets with low levels of precursor FAs. The characteristic physiological plasticity of Gulf killifish is exemplified in the nutritional domain by its management of dietary FA deficiency.

Diet-induced fatty acid variation in critical tissues of a spawning estuarine fish and consequences for larval fitness.

Freshwater and marine fishes exhibit a dichotomy in biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs) from shorter-chain precursors. Marine species generally lack this ability due to deficiencies in requisite desaturase or elongase enzymes. Gulf killifish Fundulus grandis is a euryhaline cyprinodont whose fatty acid (FA) dynamics have not been previously examined. We utilized experimental variations in exogenous FAs available to spawning F. grandis in order to construct a multitissue evaluation of FA allocation and quantify effects on reproductive output and offspring fitness. No significant decrease in fecundity occurred in animals consuming low levels of LC-PUFAs, although embryo viability rates were affected. Maternal dietary FA variation did produce differences in starvation tolerance, hypoosmoregulatory ability, and acute thermal stress tolerance for larvae. These variations occurred at elevated salinities and temperatures seldom if ever encountered by F. grandis in culture or natural environments and are unlikely to affect larval survival in these settings. FA composition of eggs and tissues from spawning females suggested potential biosynthesis of LC-PUFAs from shorter-chain precursors in F. grandis. Results of this study suggest that F. grandis possesses physiological mechanisms allowing maintenance of reproductive function when subjected to dietary deficiencies in FAs generally considered essential for marine fishes.

Metabolic and embryonic responses to terrestrial incubation of Fundulus grandis embryos across a temperature gradient

This study simulated terrestrial incubation and measured rates of embryogenesis, nitrogen elimination, heart rate, lactate production, maximum length of time a hatch could be delayed and developmental responses of terrestrially incubated Gulf killifish Fundulus grandis embryos at temperatures ranging from 20 to 30° C. Temperature had a positive relationship with rate of embryogenesis, but a negative relationship with extent of extended incubation. The 30° C treatment reached embryonic maturity 6 days before the 20° C treatment. Embryos hatched between intervals of 240 and 336, 144 and 288, 96 and 240 and 96 and 192 h after reaching developmental maturity for the 20, 23, 26 and 30° C treatments. Significantly higher concentrations of total nitrogen, in the form of ammonia and urea, were recorded in the 20 and 30° C treatments. While temperature significantly influenced lactate and ATP concentrations, no significant influence of time of incubation was detected. Terrestrial embryos displayed an ability to develop quickly during embryogenesis and prolong incubation for an extended period of time after reaching embryonic maturity. This adaptation may be a life-history trait used to minimize asynchronous hatching, cannibalism and cohort size heterogeneity.

Physiological and reproductive response to varying quantitative lipid inclusion in diets for Gulf killifishFundulus grandisBaird and Girard

Successful culture of Gulf killifish Fundulus grandis as a live marine baitfish in the south-eastern United States has experienced low fecundity as a primary restriction. Hence, the ability to optimize reproduction in captive populations may increase the potential for viable large-scale production. Broodfish nutrition is an expanding field of aquaculture, and improved nutritional status has been shown to increase reproductive output in some cultured fish. This study examined changes in quantitative inclusion of lipid as fish oil in complete diets fed to actively spawning Gulf killifish and its effects on physiological and reproductive parameters and subsequent larval morphometrics. An increase in dietary lipid levels across a gradient from 4.0 to 13.8% did not affect periodic fecundity, egg size, embryo viability rate, sperm motility, hepatosomatic index or liver total lipid content. Intraperitoneal fat increased significantly in fish fed higher lipid levels, while gonadosomatic index was significantly higher in the lowest lipid content group. Larvae produced by fish fed higher lipid levels had significantly increased endogenous nutritional resources at hatch while standard length was unaffected. No strong reproductive benefits of increased lipid inclusion were found in Gulf killifish.

Intraspecific variation in reproductive potential with maternal body size in Gulf killifish Fundulus grandis

Gulf killifish Fundulus grandis show promise for commercial development as a baitfish species marketed to anglers on the U.S. Gulf Coast. Additionally, fishes in the genus Fundulus are increasingly cultured as model organisms for various fields of scientific inquiry. Research examining effects of maternal body size on reproduction in this genus and more generally in fractional spawning species with eggs capable of terrestrial development is lacking. The present study assessed the effects of female body size on reproductive investment in laboratory held Gulf killifish as well as subsequent implications for larvae. Larger females had significantly higher fecundity and produced individual eggs of greater volume. Gonadosomatic index more than doubled as female body mass increased from 6.9 to 12.9g, but did not increase significantly in females of body mass>12.9g. Larger eggs required significantly longer incubation periods, and newly hatched larvae from larger eggs had more endogenous nutritional resources but shorter body length. Experimental results describe maternal effects in a fractional spawning species producing eggs with the ability to incubate terrestrially. Results also provide practically useful information for aquaculturists as F. grandis are increasingly cultured commercially and in laboratory settings.

Effects of potassium ion supplementation on survival and ion regulation in Gulf killifish Fundulus grandis larvae reared in ion deficient saline waters

Teleost fish often live in an environment in which osmoregulatory mechanisms are critical for survival and largely unknown in larval fish. The effects of a single important marine ion (K+) on survival and ion regulation of larval Gulf killifish, an estuarine, euryhaline teleost, were determined. A four-week study was completed in four separate recirculating systems with newly hatched larvae. Salinity in all four systems was maintained between 9.5 and 10‰. Two systems were maintained using crystal salt (99.6% NaCl) with K+ supplementation (1.31±0.04mmol/L and 2.06±0.04mmol/L K+; mean±SEM), one was maintained with crystal salt and no K+ supplementation (0.33±0.05mmol/L K+), the fourth system was maintained using a standard marine mix salt (2.96±0.04mmol/L K+), the salt mix also included standard ranges of other ions such as calcium and magnesium. Larvae were sampled throughout the experiment for dry mass, Na+/K+-ATPase (NKA) activity, whole body ion composition, relative gene expression (NKA, Na+/K+/2Cl− cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR)), and immunocytochemistry staining for NKA, NKCC, and CFTR. Larvae stocked into water with no K+ supplementation resulted in 100% mortality within 24h. Mortality and dry mass were significantly influenced by K+ concentration (P≤0.05). No differences were observed among treatment groups for NKA activity. At 1dph NKA mRNA expression was higher in the 0.3mmol [K+] group than in other treatment groups and at 7dph differences in intestinal NKA and CFTR staining were observed. These data indicate that the rearing of larval Gulf killifish may be possible in ion deficient water utilizing specific ion supplementation.

The Role of Polyamines in Osmotic Stress Tolerance in Gulf Killifish Fundulus grandis

Polyamines are a family of low molecular weight organic cations produced in part by the coordinated actions of arginase II (Arg II) and ornithine decarboxylase (Odc). Although little is known of their functions in fish, polyamines have been implicated in diverse physiological processes. We describe a possible role of polyamines in hypoosmotic tolerance in the gulf killifish, Fundulus grandis, a species known to tolerate acute fluctuations in wide salinity range. Adult fish were reared in 5 ppt water for at least 1 month, and acutely transferred to 0.1, 0.5, 1, 2, and 5 ppt. Fish were randomly sampled from each salinity at 6 h, 1 d, 3 d, and 7 d post‐transfer. We have shown that relative Arg II and Odc mRNA levels, and Odc protein activity are highly up‐regulated in the gills. Hypoosmotic exposure also increases the concentration of the polyamines, putrescene, spermidine, and spermine. Although gill putrescine levels remain elevated throughout the first 7 days post ‐ transfer to freshwater, the concentrations of spermidine and spermine decrease with time suggesting a catabolic regulation of compounds. We are investigating the role of polyamine catabolism in apoptosis during salinity‐induced gill remodeling.

Embryonic development and metabolic costs in Gulf killifish Fundulus grandis exposed to varying environmental salinities

The Gulf killifish (Fundulus grandis) is a euryhaline fish found in coastal marsh along the entire of Gulf of Mexico and southern Atlantic of coast of the United States. The objective of this study was to investigate the effects of salinity on embryogenesis in the Gulf killifish. Four recirculation systems at salinities of 0.4, 7, 15, and 30g/L were maintained at a static temperature with flow-through trays, containing embryos (n=39) placed in triplicate into each system. Throughout embryogenesis, the rate of development, ammonia and urea excretion, and heart rate were monitored. Percent hatch was recorded, and morphological parameters were measured for larvae at hatch. As salinity was increased, the rate of embryogenesis decreased. Salinity significantly affected percent hatch with an 80.0%±2.6% for 7g/L and 39.1±4.3, 45.4±4.5, and 36.3%±12.0% for 0.4, 15, and 30g/L, respectively. Salinity and stage of development significantly affected production of ammonia and urea. As salinity increased, the dominate metabolite end product changed from urea to ammonia. However, the 15g/L salinity treatment had the two highest levels of urea recorded. Heart rate was unaffected by salinity but increased throughout embryogenesis and remained constant once embryos reached stages where hatching has been recorded. While mean total length was not affected by salinity, embryos incubated in 30g/L produced larvae with significantly thicker body depth at hatch. The 0.4, 7, and 15g/L salinity treatments all had similar mean hours to hatch. The 30g/L treatment resulted in a significantly longer mean time to hatch and smaller body cavity area at hatch.