Social hierarchy,shelter use,and avoidance of predatory toadfish (Opsanus tau) by the striped blenny (Chasmodes bosquianus)

This paper describes a three-part examination of the predatory relationship between oyster toadfish (Opsanus tau) and striped blennies (Chasmodes bosquianus). In the first laboratory study, blennies avoided the toadfish when placed in a choice situation. During the second laboratory study, dominant blennies escaped attack significantly more than did subordinates by using a protective shelter. A field study demonstrated that toadfish will attack active but tethered blennies under natural conditions. As predators, toadfish appear to use a mixed strategy. During the day, when they are relatively inactive, they may feed as ambush predators. However, we suggest that at night they move about actively, stalking benthic invertebrates and small fishes. They also feed as scavengers, consuming a variety of foods.     

Absence of a seasonal cycle in the sonic neuromuscular system of the oyster toadfish

No seasonal pattern was found in total swimbladder weight, sonic muscle weight, or spinal sonic motor nucleus neuron soma size of the oyster toadfish Opsanus tau , indicating that additional nonsteroidal factors are also involved in the development of the toadfish sonic neuromuscular system.     

Parvalbumin expression in trout swimming muscle correlates with relaxation rate

Rainbow trout (Oncorhynchus mykiss) display longitudinal and developmental shifts in muscle relaxation rate. This study aimed to determine the role of variations in parvalbumin content in modulating muscle relaxation. Parvalbumin is a low molecular weight protein that buffers myoplasmic Ca2+ and enhances muscle relaxation. In some fish, longitudinal variations in muscle relaxation have been linked to variations in the total amount of parvalbumin present in muscle and in the relative expression of two parvalbumin isoforms. We have demonstrated previously that anterior slow-twitch or red myotomal muscle relaxes more rapidly than that from the posterior for both rainbow and brook trout. Further, younger rainbow trout parr have faster red muscle relaxation rates than older smolts. Here we report similar results for fast-twitch or white muscle. We quantified the parvalbumin expression in red and white muscle from different body positions of rainbow trout parr and smolts and for brook trout (Salvelinus fontinalis) adults. There was a significant shift in total parvalbumin content of muscle: the faster muscle from the anterior myotome contained greater amounts of parvalbumin. For brook trout, longitudinal variation in relaxation rate was also associated with shifts in the relative expression of the two parvalbumin isoforms. The faster muscle of parr contained more parvalbumin. Lastly, trout white muscle tended to have higher levels of parvalbumin and greater levels of the Parv2 (relative to Parv1) isoform as compared to red muscle. Parvalbumin expression correlated with muscle relaxation rate in trout, although there were species-specific differences in the importance of altering total parvalbumin content versus shifts in relative parvalbumin isoform expression.     

Age,growth rate and feeding habits of the oyster toadfish,Opsanus tau (Linnaeus) in South Carolina

Age, gonad state, gut content, and length-weight relationships were analyzed for oyster toadfish, Opsanus tau (Linnaeus), caught in 1978–1980 at Hilton Head, South Carolina, Toadfish Tournaments. Examination of the otoliths revealed ages that ranged from < 1 to 8 yr, with a median age of 3 yr. Fish were sexually mature between years 2 to 7. Combined length-weight data provided a linear regression line value of W_L = 4.9e^0.017L; the age-weight relationship was W_t = 26.5e^0.52t. An unexploited fishery is suggested by the data.     

Metabolic fate of exogenous 15NH4Cl in the gulf toadfish (Opsanus beta)

This study was undertaken to determine whether gulf toadfish (Opsanus beta) could metabolize ammonia from their environment into other, less toxic products. To this end, gulf toadfish were exposed to 3.8 mM 15NH(4)Cl in seawater for 24 and 48 h. Liver, kidney, gill, brain and muscle samples were analyzed for distribution of 15N within the tissue and among various nitrogen-containing metabolites (ammonia, amino-N, glutamine-N, urea and protein). The data reported here show that the toadfish can indeed take up and metabolize ammonia. Analysis of individual metabolic products of ammonia indicates that the toadfish can convert this toxic chemical into other less toxic metabolites. Ammonia enrichment is significantly different over controls in the kidney, brain and muscle. Urea enrichment is most significant in the brain, with less significant enrichment occurring in the liver and muscle. While accumulation of ammonia into an amino acid pool was not a significant metabolic fate, protein synthesis was significantly enriched in all tissues (with the highest levels occurring in the gill) indicating that amino acid synthesis may be a pathway of ammonia detoxification en route to protein synthesis, and that environmental ammonia can be 'fixed' into protein. Finally, it was found that glutamine-N synthesis occurs at significant levels in the liver, brain and muscle.     

Intracellular vesicular trafficking in the gill epithelium of urea-excreting fish

Most teleost fish are ammoniotelic, and relatively few are ureotelic, in which the majority of nitrogenous waste is excreted as urea. This study aimed to determine whether the gill ultrastructure of ureotelic fish might have specific, unique characteristics compared with ammoniotelic fish. The gill morphology was studied in three closely related species of the family Batrachoididae: Opsanus beta, the gulf toadfish; Opsanus tau, the oyster toadfish; and Porichthys notatus, the plainfin midshipman, because prior studies have demonstrated that the two former species are ureotelic and excrete urea in unique, short daily pulses, whereas the latter is ammoniotelic. Ultrastructural studies demonstrated significant trafficking of dense-cored vesicles (50-200 nm) between the Golgi apparatus and the apical membrane of epithelial cells surrounding gill filaments and lamellae in these two Opsanus spp. The material constituting the core of these vesicles was intensely stained by lead salt and was unloaded externally when vesicles contacted the apical membrane. Another characteristic of these urea-secreting fish was the presence of numerous large, black-stained lysosomes, which contained cored vesicles, suggesting a second destination for the dense-cored vesicles. As a working hypothesis, the present data suggest that the urea-transporter protein, recently found in toadfish gills, is inserted in the vesicle. Subsequently, it could serve to either sequester cytosolic urea that ultimately is secreted into the water after contact of these vesicles with the pavement cell apical membrane, or it could allow facilitated diffusion of urea across the plasma membrane following insertion into the membrane. As further comparative evidence, the ammoniotelic P. notatus exhibited neither the vesicular trafficking nor the population of lysosomes both found in Opsanus spp.     

Immunohistochemical localization of urea and ammonia transporters in two confamilial fish species, the ureotelic gulf toadfish (Opsanus beta) and the ammoniotelic plainfin midshipman (Porichthys notatus)

This study aims to illustrate potential transport mechanisms behind the divergent approaches to nitrogen excretion seen in the ureotelic toadfish (Opsanus beta) and the ammoniotelic plainfin midshipman (Porichthys notatus). Specifically, we wish to confirm the expression of a urea transporter (UT), which is found in the gill of the toadfish and which is responsible for the unique “pulsing” nature of urea excretion and to localize the transporter within specific gill cells and at specific cellular locations. Additionally, the localization of ammonia transporters (Rhesus glycoproteins; Rhs) within the gill of both the toadfish and midshipman was explored. Toadfish UT (tUT) was found within Na⁺-K⁺-ATPase (NKA)-enriched cells, i.e., ionocytes (probably mitochondria-rich cells), especially along the basolateral membrane and potentially on the apical membrane. In contrast, midshipman UT (pnUT) immunoreactivity did not colocalize with NKA immunoreactivity and was not found along the filaments but instead within the lamellae. The cellular location of Rh proteins was also dissimilar between the two fish species. In toadfish gills, the Rh isoform Rhcg1 was expressed in both NKA-reactive cells and non-reactive cells, whereas Rhbg and Rhcg2 were only expressed in the latter. In contrast, Rhbg, Rhcg1 and Rhcg2 were expressed in both NKA-reactive and non-reactive cells of midshipman gills. In an additional transport epithelium, namely the intestine, the expression of both UTs and Rhs was similar between the two species, with only subtle differences being observed.     

The ontogeny of haematopoiesis in the marine teleost Leiostomus xanthurus and a comparison of the site of initial haematopoiesis with Opsanus tau

The ontogeny of haematopoiesis in the perciform fish, spot Leiostomus xanthurus , differed from that reported as the norm for fishes, as exemplified by the cypriniform zebrafish Danio rerio , and observed in the batrachoidiform oyster toadfish Opsanus tau . Erythropoiesis in spot was first evident in the head kidney of yolk‐sac larvae 3 days after hatching (DAH). No embryonic intermediate cell mass (ICM) of primitive stem cells or blood islands on the yolk were apparent within embryos. Erythrocytes were first evident in circulation near the completion of yolk absorption, c . 5 DAH, when larvae were c . 2·0 mm notochord length ( L _N). Erythrocyte abundance increased rapidly with larval development for c . 14 to 16 DAH, then became highly variable following changes in cardiac chamber morphology and volume. Erythrocytic haemoglobin (Hb) was not detected within whole larvae until they were 12 DAH or c . 3·1 mm L _N, well after yolk and oil‐globule absorption. The Hb was not quantified until larvae were >47 DAH or >7 mm standard length. The delayed appearance of erythrocytes and Hb in spot was similar to that reported for other marine fishes with small embryos and larvae. In oyster toadfish, a marine teleost that exhibits large embryos and larvae, the ICM and Hb were first evident in two bilateral slips of erythropoietic tissue in the embryos, c . 5 days after fertilization. Soon thereafter, erythrocytes were evident in the heart, and peripheral and vitelline circulation. Initial haematopoiesis in oyster toadfish conformed with that described for zebrafish. While the genes that code for the development of haematopoiesis are conserved among vertebrates, gene expression lacks phylogenetic pattern among fishes and appears to conform more closely with phenotypic expression related to physiological and ecological influences of overall body size and environmental oxygen availability.     

Higher levels of aggression are observed in socially dominant toadfish treated with the selective serotonin reuptake inhibitor, fluoxetine

The following study set out to test the hypothesis that acute treatment with the selective serotonin reuptake inhibitor, fluoxetine, would result in a rise in circulating 5-HT levels and consequently a decrease in territorial aggression in the Gulf toadfish, Opsanus beta. Size-matched pairs of toadfish were implanted intraperitoneally with the same dose of fluoxetine (0, 10 or 25 μg g^− 1). After a social interaction between a pair of fish, circulating levels of serotonin (5-HT; 5-hydroxytryptamine) and cortisol were measured and relative mRNA expression of the 5-HT_1A receptor in the toadfish brain was determined using quantitative (real-time) PCR (qPCR). Behavioral endpoints such as the number of aggressive acts and swimming activity were also quantified so that dominant and subordinate fish could be identified. Fluoxetine treatment resulted in an increase in circulating levels of 5-HT, regardless of social status. Circulating cortisol concentrations were unaffected by fluoxetine, but were significantly higher in subordinate individuals when compared to dominant fish. Toadfish brain 5-HT_1A receptor mRNA expression was not affected by treatment or social status. Lastly and contrary to our predictions, fluoxetine treatment resulted in an increase in the number of aggressive acts made by dominant individuals, with no differences in the level of aggression or swimming activity of subordinate fish. This study is the first to describe elevated aggression in a teleost fish with elevated circulating levels of 5-HT.     

Real-time measurement of the rate of sarcoplasmic reticulum calcium pumping in skinned muscle fibers

A method and a device had been developed to directly measure the accumulation of calcium in the sarcoplasmic reticulum and its release from the sarcoplasmic reticulum, depending on the free Ca²⁺ concentration in the solution. The sarcoplasmic reticulum occupies to 30% of the volume of the swim bladder muscles of the oyster toadfish Opsanus tau. To isolate and skin muscle fibers and to remove the accumulated calcium from the sarcoplasmic reticulum, a set of solutions containing EGTA as a pCa buffer was used. To measure the calcium exchange between a fiber ～10 nl in volume and the solution in a 5-μl cuvette, instead of EGTA, 50–100 μM FURA2 or bisFURA2 was used both as pCa buffer and as a fluorescent indicator of the calcium concentration in the cuvette. An increase in fluorescence intensity meant an increase in the free FURA concentration in the solution surrounding the fiber since the calcium entering the sarcoplasmic reticulum was taken from this solution. The slope of the fluorescence curve corresponded to a rate of calcium accumulation in the sarcoplasmic reticulum of 1.6 μmol per second per liter of the solution in the cuvette or 2.6 mmol per second per liter of the sarcoplasmic reticulum. A solution without oxalate and ruthenium red may exhibit oscillations of the free FURA concentration, which can be explained by calcium-activated calcium release from the sarcoplasmic reticulum.     

Inverse Regulation of the Cytosolic Ca2+ Buffer Parvalbumin and Mitochondrial Volume in Muscle Cells via SIRT1/PGC-1α Axis

Skeletal muscles show a high plasticity to cope with various physiological demands. Different muscle types can be distinguished by the force, endurance, contraction/relaxation kinetics (fast-twitch vs. slow-twitch muscles), oxidative/glycolytic capacity, and also with respect to Ca²⁺-signaling components. Changes in Ca²⁺ signaling and associated Ca²⁺-dependent processes are thought to underlie the high adaptive capacity of muscle fibers. Here we investigated the consequences and the involved mechanisms caused by the ectopic expression of the Ca²⁺-binding protein parvalbumin (PV) in C2C12 myotubes in vitro, and conversely, the effects caused by its absence in in fast-twitch muscles of parvalbumin null-mutant (PV−/−) mice in vivo. The absence of PV in fast-twitch muscle tibialis anterior (TA) resulted in an increase in the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and of its positive regulator, the deacetylase sirtuin 1 (SIRT1). TA muscles from PV−/− mice also have an increased mitochondrial volume. Mild ionophore treatment of control (PV-devoid) C2C12 myotubes causing a moderate elevation in [Ca²⁺]_c resulted in an increase in mitochondrial volume, together with elevated PGC-1α and SIRT1 expression levels, whilst it increased PV expression levels in myotubes stably transfected with PV. In PV-expressing myotubes the mitochondrial volume, PGC-1α and SIRT1 were significantly lower than in control C2C12 myotubes already at basal conditions and application of ionophore had no effect on either one. SIRT1 activation causes a down-regulation of PV in transfected myotubes, whilst SIRT1 inhibition has the opposite effect. We conclude that PV expression and mitochondrial volume in muscle cells are inversely regulated via a SIRT1/PGC-1α signaling axis.     

Variability in the role of the gasbladder in fish audition

The teleost gasbladder is believed to aid in fish audition by transferring pressure components of incoming sound to the inner ears. This idea is primarily based on both anatomical observations of the mechanical connection between the gasbladder and the ear, followed by physiological experiments by various researchers. The gasbladder movement has been modeled mathematically as a pulsating bubble. This study is extending the previous work on fish with a physical coupling of the gasbladder and ear by investigating hearing in two species (the blue gourami Trichogaster trichopterus, and the oyster toadfish Opsanus tau) without a mechanical linkage. An otophysan specialist (the goldfish Carassius auratus) with mechanical coupling, is used as the control. Audiograms were obtained with acoustically evoked potentials (e.g., auditory brainstem response) from intact fish and from the same individuals with their gasbladders deflated. In blue gourami and oyster toadfish, removal of gas did not significantly change thresholds, and evoked potentials had similar waveforms. In goldfish thresholds increased by 33–55 dB (frequency dependent) after deflation, and major changes in evoked potentials were observed. These results suggest that the gasbladder may not serve an auditory enhancement function in teleost fishes that lack mechanical coupling between the gasbladder and the inner ear. Accepted: 28 February 2000     

The amino acid sequence of the parvalbumin from the very fast swimbladder muscle of the toadfish (Opsanus tau)

1. The parvalbumin from the very fast striated muscle of the swimbladder of the toadfish (Opsanus tau) has been purified to homogeneity and its amino acid sequence has been completely elucidated. 2. The polypeptide chain is made of 109 residues, belongs to the beta group of parvalbumins and presents characteristics common to many other parvalbumins, i.e. a blocked N-terminal group, a cysteine and an arginine residue at positions 18 and 75 respectively and a quadruplet of acidic residues in the region 59-62.     

Protein differentiation of the superfast swimbladder muscle of the toadfish Opsanus tau

The superfast swimbladder muscle of Opsanus tau differs from the corresponding fast skeletal muscle not only by its well known much more developed sarcoplasmic reticulum but also by its two- to threefold higher parvalbumin contact and a genuine LC₂ myosin light chain.     

GEOGRAPHIC POPULATION STRUCTURE AND SPECIES DIFFERENCES IN MITOCHONDRIAL DNA OF MOUTHBROODING MARINE CATFISHES (ARIIDAE) AND DEMERSAL SPAWNING TOADFISHES (BATRACHOIDIDAE)

Restriction-fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to evaluate population-genetic structure and matriarchal phylogeny in four species of marine fishes that lack a pelagic larval stage: the catfishes Arius felis and Bagre marinus, and the toadfishes Opsanus tau and O. beta. Thirteen informative restriction enzymes were used to assay mtDNAs from 134 specimens collected from Massachusetts to Louisiana. Considerable genotypic diversity was observed in each species. However, major mtDNA phylogenetic assemblages in catfish and toadfish (as identified in Wagner networks and UPGMA phenograms) exhibited contrasting patterns of geographic distribution: in catfish, distinct mtDNA clades were widespread, while such clades in toadfish tended to be geographically localized. By both the criteria of species' ranges and the geographic pattern of intraspecific mtDNA phylogeny, populations of marine catfish in the western Atlantic have had greater historical interconnectedness than have toadfish. Results are also compared to previously published mtDNA data in freshwater and other marine fishes. Although mtDNA differentiation among conspecific populations of continuously distributed marine fishes is usually lower than that among discontinuously distributed freshwater species inhabiting separate drainages, it is apparent that historical biogeographic factors can importantly influence genetic structure in marine as well as freshwater species.     

Parvalbumin expression is downregulated in rat fast-twitch skeletal muscles during aging

In this study, the protein expression profile of extensor digitorum longous (EDL) and Soleus (SOL) muscles, representing fast- and slow-twitch skeletal muscles, respectively, was established using high resolution two-dimensional electrophoresis (2-DE). One protein spot was found uniquely expressed in EDL muscle. N-terminal sequence analysis identified the protein as parvalbumin. Parvalbumin is a high affinity calcium binding protein that regulates muscle contraction and relaxation. Our experiments revealed that parvalbumin expression in EDL muscle was down-regulated during aging. In addition, high-intensity exercise could reverse this age-related change. Soleus muscles do not normally express parvalbumin, but high-intensity exercise could ectopically induce its expression in both young and old SOL muscles. We have also confirmed our 2-DE findings by immunohistochemistry on muscle sections. Our results suggest that high-intensity training could be used to improve muscle functions during aging because parvalbumin play an important role in regulating skeletal muscle contraction and relaxation.     

Field studies on the ureogenic gulf toadfish, in a subtropical bay. II. Nitrogen excretion physiology

In order to examine the in situ nitrogen excretion physiology of gulf toadfish ( Opsanus beta ) (Fam. Batrachoididae), several biochemical and physiological measurements relating to urea synthesis and excretion were measured in samples taken from freshly collected gulf toadfish from a subtidal population in Biscayne Bay, Florida, U.S.A. This indirect appoach was used, instead of direct measurements of nitrogen excretion, because nitrogen excretion patterns of gulf toadfish are altered markedly during the first 24 h of capture disturbance or laboratory confinement. The values obtained for plasma cortisol levels, and the activities of hepatic ornithine-urea cycle enzymes, including glutamine synthetase (and its partitioning between cytosolic and mitochondrial compartments), suggest that gulf toadfish in Biscayne Bay may excrete a substantial portion of their waste nitrogen as urea. Also conducted were correlation analyses of several biotic variables (plasma [cortisol], enzyme activities, plasma [urea], hepatosomatic index, and plasma [Ca⁺⁺]) with several abiotic variables (temperature, salinity, depth and dissolved oxygen), and with collection site and season. Results of these analyses are discussed in the context of hypotheses to explain ureotely in this teleost fish.     

Pulsatile urea excretion in Gulf toadfish: the role of circulating serotonin and additional 5-HT receptor subtypes

Journal of Comparative Physiology B - The neurochemical serotonin (5-HT) is involved in stimulating pulsatile urea excretion in Gulf toadfish (Opsanus beta) through the 5-HT2A receptor; however, it...     

Experimental assessment of trophic impacts from a network model of a seagrass ecosystem: Direct and indirect effects of gulf flounder, spot and pinfish on benthic polychaetes

Trophic cascades are predicted to occur when the abundance of predators is increased, directly reducing the abundance of the intermediate prey and indirectly increasing the abundance of the prey at the base of a food web. Mixed trophic impact analysis of a network model developed for Apalachee Bay, near St. Marks, FL, USA predicted such a trophic cascade, in that increased abundance of juvenile gulf flounder Paralichthys albigutta (x¯ = 149 mm SL, effective trophic level 3.9) should have a negative impact on juvenile spot Leiostomus xanthurus (x¯ = 30 mm SL, effective trophic level 2.9) and a positive impact on benthic polychaetes (effective trophic levels 2.3 for deposit feeders and 3.0 for predatory polychaetes) in Halodule wrightii seagrass beds. We tested the predictions of the mixed trophic impact analysis by manipulating the abundance of the high trophic-level species (juvenile gulf flounder) in a cage-exclusion study in the North River, near Harkers Island, NC, USA. We compared the polychaete communities in St. Marks, FL and Harkers Island, NC, and showed that they are 51% similar (Jaccard's Index) at the family level, with the same eight dominant families (Nereidae, Capitellidae, Syllidae, Spionidae, Cirratulidae, Terebellidae, Sabellidae, and Maldanidae) present in both locations. We used 24 open-bottom cages to enclose the benthos and its seagrass-associated animal communities. We manipulated each cage by assigning it to one of the following treatments: (1) inclusion of fishes in upper and intermediate trophic levels (1 juvenile gulf flounder and 10 juvenile spot, the flounder + spot treatment); (2) inclusion of the intermediate predator (10 juvenile spot with no gulf flounder, the spot-only treatment); and (3) no fish added (unmanipulated controls). Core samples taken within the cages provided pre- and post-experimental measures of polychaete density and biomass, and the difference in density and biomass were used as response variables. At the end of the experiment, we collected, weighed, and analyzed the gut contents of all juvenile spot present in the cages. Juvenile pinfish (Lagodon rhomboides, x¯ = 30 mm SL) were present at the end of the study, having arrived as larvae or being trapped during cage set-up, and these fish were also examined, because they also eat polychaetes and their natural densities exceeded our introduced spot densities. Significant differences among treatments were detected for the polychaete family Terebellidae for both the change in density and biomass (pre-experiment − post-experiment). Densities of the Terebellidae changed in the direction predicted by the network model's impact analysis, declining in the cages with spot added compared with the control cages. Analyses of the other response variables (post-experiment spot and pinfish densities and biomass, difference between pre- and post-experiment polychaete densities and biomass for other families, and post-experiment spot and pinfish stomach content biomass) showed no significant differences among treatments. Several variables (Nereidae densities, pinfish densities and biomass, and pinfish stomach content biomass) varied between cages with low and high seagrass cover (significant blocking effect, P < 0.001). Nereidae densities declined significantly in cages with high (73%) rather than with low coverage (31% cover) of seagrass. Pinfish density and biomass were significantly greater in the high seagrass cages at the end of the experiments (P < 0.001), suggesting that dense seagrass attracted them. We conclude that the high density of pinfish in dense seagrass was responsible for the decline in density of the Nereidae. The direct effect of intermediate predators (pinfish feeding on polychaete prey) can be influenced by preferential recruitment of fishes to structurally complex habitats. The direction of change of indirect effects, but not the magnitude, in multi-trophic-level food webs can be predicted by the mixed trophic impact analysis of network models. However, these indirect effects are likely to be small in magnitude relative to direct effects and may be difficult to detect experimentally, especially in low-power experimental caging studies with natural fluctuations in recruitment rates of competitor species.