Site fidelity, home range, and tidal migrations of juvenile pinfish, Lagodon rhomboides, in salt marsh creeks

We conducted a series of experiments to determine the movements and fidelity of juvenile pinfish, Lagodon rhomboides, in salt marsh creeks within North Inlet Estuary, SC. In Experiment 1, we investigated the fidelity of pinfish (40–100mm SL) at four subtidal locations (9–617m apart) along the axis of a major creek. We trapped and marked 2,297 individuals and recaptured 15–22% of the fishes released at each site, almost all of which (99.7%) had been marked at the same location of recapture up to 3 months earlier. In Experiment 2, we investigated pinfish movements between subtidal and intertidal areas. In the 8 weeks prior to sampling 2 intertidal creeks, we marked 950 juveniles in the adjacent subtidal areas. Sampling of the 2 flooded intertidal creeks showed that 9–20% of the pinfish collected bore marks, and all had been previously marked at the subtidal site immediately adjacent to the intertidal creek. Gut analysis of 60 individuals revealed that juveniles collected from the intertidal areas at high tide had consumed about ten times more food than those collected at the subtidal sites at low tide. In Experiment 3, we determined the fidelity of recently settled pinfish (<35mm SL) and showed that 15% of the 434 marked pinfish remained in the same area; some were at liberty up to 7 weeks. In Experiment 4, we determined home range by tagging and recapturing juvenile pinfish at sites separated by 20m along a 200m subtidal transect. We estimated that during periods when the intertidal zone was not accessible, the average home range was 9.4m with only 10% of tagged fish moving greater than 20m during the 4 month study. Our results indicate that soon after recruitment to the estuary, pinfish establish strong fidelity for sites within salt marsh creeks and exhibit tidal periodicity in both movements and feeding.     

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.     

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.     

Directional and frequency response characteristics in the descending octaval nucleus of the toadfish (Opsanus tau)

This study is a continuation of a long-term investigation of the auditory circuit in the oyster toadfish, Opsanus tau. Input from the auditory periphery projects to the ipsilateral descending octaval nucleus (DON). Ipsilateral and contralateral DONs project to the auditory midbrain, where a previous study indicated that both frequency tuning and directional sharpening are present. To better understand the transformation of auditory information along the auditory pathway, we have examined over 400 units in the DON to characterize frequency and directional information encoded in the dorsolateral division of the nucleus. Background activity was primarily low (<10 spikes/s) or absent. The maximum coefficient of synchronization was equivalent to the periphery (R = 0.9) and substantially better than in the midbrain. The majority of DON units (79%) responded best to stimulus frequencies of 84-141 Hz and were broadly tuned. DON cells retain or enhance the directional character of their peripheral input (s); however, characteristic axes were distributed in all quadrants around the fish, providing further evidence that binaural computations may first occur in the DON of this species.     

Intestinal zinc uptake in two marine teleosts,squirrelfish (Holocentrus adscensionis) and gulf toadfish (Opsanus beta)

Zinc is a vital micronutrient, yet as an environmental toxicant it can be deleterious to aquatic organisms such as fish. Consequently, the study of zinc uptake mechanisms is essential for understanding nutrition, toxicity, and metabolism of this metal. Intestinal zinc uptake was studied in two marine teleosts, using both in vitro (in vitro perfusion and intestinal sacs) and in vivo techniques (in situ bolus). Female squirrelfish (Holocentrus adscensionis) exhibited significantly increased epithelial zinc uptake associated with enhanced hepatic zinc accumulation. This confirms this zinc-hyperaccumulating teleost as a potential model of zinc absorption. Intestinal zinc uptake in the gulf toadfish (Opsanus beta) was biphasic with respect to zinc concentration (0.3-500 microM), exhibiting both saturable and passive uptake components. In both species, the passage of zinc into the postintestinal compartment was highly dependent on technique. Decreased proportions of postintestinal zinc in vivo, coupled with concentration-dependent distribution of zinc accumulation, suggested mechanisms may act to control the movement of zinc into the circulation. In addition, the results of this study were used to reinterpret previous findings of zinc uptake in freshwater fish and allowed a critique of techniques used to study intestinal metal uptake.     

5-Hydroxytryptamine initiates pulsatile urea excretion from perfused gills of the gulf toadfish (Opsanus beta)

When stressed, toadfish become ureotelic and excrete almost all of their nitrogenous waste in 1-3 daily pulses of urea-N across the gills. Intravascular injections of 5-hydroxytyptamine (5-HT; serotonin) and analogues also elicit marked excretory pulses of urea-N from toadfish in vivo, suggesting that 5-HT release is the proximate trigger for spontaneous pulses. However it is unclear whether 5-HT is acting on the gills directly or elsewhere to cause the effect indirectly. A perfused whole gill preparation which maintained normal pressure relationships and stable vascular resistance was employed to address this question. Bolus injections into the ventral aortic perfusate of either 5-HT (1, 10 μmol kg(-1)) or the specific 5-HT(2) receptor agonist α-methyl 5-HT (1, 10 μmol kg(-1)) elicited rapid urea-N pulses from perfused toadfish gills. The effective doses, the post-injection delays (5.5 ± 1.3 min, range=2-22), the percent occurrences (57-85%), and the magnitude of the induced urea-N pulses (615.4 ± 131.3 μmol-N kg(-1), range 66.0-2634.0), were all similar to those previously reported when these agents were injected in vivo. Bolus injections of 5-HT and α-methyl 5-HT also elicited a biphasic response in ventral aortic pressure, reflecting an initial rapid short-lived vasodilation and a subsequent longer-lasting vasoconstriction. These events were similar to those which have been recorded to occur at a greater frequency during spontaneous urea-N pulsing in vivo. Neither the urea-N pulsing nor the cardiovascular responses to 5-HT were inhibited by the 5-HT(2A) receptor subtype blocker, ketanserin (pre-injection with 10 μmol kg(-1) plus 33 μmol L(-1) in the perfusate). Overall, these results provide strong support for the idea that the proximate stimulus for natural urea pulsing in vivo is 5-HT mobilization, acting directly in the gills.     

Activation and detoxication of promutagens by toadfish (Opsanus tau) hepatic postmitochondrial fractions in the Salmonella assay

Three groups of experiments were conducted to characterize the hepatic postmitochondrial fraction (S9) from the oyster toadfish (Opsanus tau) as an activation system for promutagens in the Salmonella assay and to provide an initial evaluation of the extent to which data from standard in vitro assays with mammalian activation systems are predictive of possible genotoxic effects in this marine fish. In the first group of experiments the effects of increasing the concentration of S9 from untreated and 3-methylcholanthrene (MC)- or Aroclor 1254 (AC)-pretreated toadfish and Sprague-Dawley rats on the mutagenicities of different concentrations of 2-aminoanthracene (2AA) and benzo[a]pyrene (BAP) were examined in Salmonella (TA98) plate assays. The maximum levels of 2AA mutagenicity attained by S9 from untreated (UI S9) toadfish and rats were comparable, but UI S9 from toadfish was moreeffective than UI S9 from rats in mediating BAP mutagenicity. MC pretreatment decreased maximum levels of 2AA mutagenicity and increased maximum levels of BAP mutagenicity mediated by S9 from both species. MC pretreatment also altered the pattern of dependence of 2AA mutagenicity on the concentration of S9 protein for S9 from both species. A similar alteration in the pattern of dependence of BAP mutagenicity on the concentration of S9 protein was also observed with S9 from MC-pretreated toadfish. Although AC pretreatment of rats effected changes in the mutagenicities of both test chemicals similar to those effected by MC pretreatment, AC pretreatment of toadfish effected little or no change in the mutagenicities of either test chemical. The changes in the pattern of dependence of 2AA and BAP mutagenicities on the concentration of S9 protein effected by MC pretreatment of toadfish were confirmed in a separate group of experiments. A third group of experiments was designed to examine the effects of α-naphthoflavone (ANF) on the mutagenicities of 2AA and BAP mediated by UI and MC S9 from toadfish. Although ANF did not affect the 2AA mutagenicity mediated by UI S9, a significant decrease in 2AA mutagenicity and a significant increase in BAP mutagenicity mediated by MC S9 and a significant decrease in BAP mutagenicity mediated by UI S9 were observed. These results indicate that 2AA and BAP are effectively activated by toadfish S9 and that, as in rats, these two test chemicals are activated and/or detoxicated by different cytochrome P-450-dependent pathways. These results also support the contention that cytochrome P-450-dependent detoxication pathways can be an important determinant of the mutagenic potency of some promutagens in vitro.     

Structure and function of the axillary organ of the gulf toadfish, Opsanus beta (Goode and Bean)

The structure of the axillary organ of a batrachoidid species, the gulf toadfish (Opsanus beta Goode and Bean 1879), has been examined and several simple experiments designed to elucidate its function performed. Electron microscopy (EM) studies revealed cells and structures suggesting secretory and iono regulatory roles (e.g., abundant intracytoplasmic secretory particles, rough endoplasmic reticulum, sparse Golgi bodies, indented epithelial cells with microvilli, numerous endocytotic vesicles, etc.). Our physiological experiments allowed us to reach several conclusions: the organs do not excrete significant quantities of urea relative to other areas of the fish (head and gills), the organs do not secrete a substance that is toxic to a teleost test fish (Gambusia affinis), the secretions do not induce short-term modifications in locomotory activity of other gulf toadfish (e.g., by pheromonal means) and the secretions do not inhibit the growth of several species of microorganisms in culture. The function of the organ and its secretions remains unknown, representing a fertile area for research on structure and function in comparative physiology.     

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.     

Directional selectivity and frequency tuning of midbrain cells in the oyster toadfish, Opsanus tau

Single-unit recordings were made from areas in the midbrain (torus semicircularis) of the oyster toadfish. We evaluated frequency tuning and directional responses using whole-body oscillation to simulate auditory stimulation by particle motion along axes in the horizontal and mid-sagittal planes. We also tested for bimodality in responses to auditory and hydrodynamic stimuli. One recording location in each animal was marked by a neurobiotin injection to confirm the recording site. Recordings were made in nucleus centralis, nucleus ventrolateralis, and the deep cell layer. Most units were frequency-selective with best frequencies between 50 and 141 Hz. Suppression of activity was apparent in 10% of the cells. Bimodality was common, including inhibition and suppression of background activity by auditory or hydrodynamic stimulation. The majority of the cells were directionally selective with directional response patterns that were sharpened compared with those of primary saccular afferents. The best directional axes were arrayed widely in spherical space, covering most azimuths and elevations. This representation is adequate for the computation of the motional axis of an auditory stimulus for sound source localization.Abbreviations BF best frequency - DCL deep cell layer - DON descending octaval nucleus - DRP directional response pattern - FFT fast Fourier transform - LL lateral lemniscus - NC nucleus centralis - NVL nucleus ventrolateralis - PVC periventricular cells - R coefficient of synchronization - TS torus semicircularis - Z Rayleigh statistic     

Mutually exclusive muscle designs: the power output of the locomotory and sonic muscles of the oyster toadfish (Opsanus tau)

Animals perform a vast array of motor activities. Although it has generally been accepted that muscles are well suited to the function that they must perform, specialization for performing one function may compromise their ability for carrying out another. We examined this principle in the toadfish muscular system: slow-twitch red and fast-twitch white myotomal muscles are used for powering swimming at relatively low frequencies, while the superfast swimbladder muscle powers mating calls by contracting at 100 Hz. We measured muscle power output over a wide range of frequencies. The red and white locomotory muscles could not generate power over ca. 2.2 and 12 Hz, respectively and, hence, could not power sound production. In contrast, the swimbladder muscle has many specializations that permit it to generate power at frequencies in excess of 100 Hz. However, these specializations drastically reduce its power output at low frequencies: the swimbladder muscle generated only one-twentieth of the power of the red muscle and one-seventh of the power of the white muscle at the frequencies used during swimming. To generate the same total power needed for swimming would require unfeasibly large amounts of swimbladder muscle that could not fit into the fish. Hence, the designs of the swimbladder and locomotory muscles are mutually exclusive.     

Ionic composition of endolymph and perilymph in the inner ear of the oyster toadfish, Opsanus tau

The concentrations of free Na+, K+, Ca(+, and Cl(-)in endolymph and perilymph from the inner ear of the oyster toadfish, Opsanus tau, were measured in vivo using double-barreled ion-selective electrodes. Perilymph concentrations were similar to those measured in other species, while endolymph concentrations were similar to those measured previously in elasmobranch fish, though significantly different from concentrations reported in mammals. Perilymph concentrations (mean +/- std. dev.) were as follows: Na+, 129 mmol l(-1) +/- 20; K+, 4.96 mmol l(-1) +/- 2.67; Ca2+, 1.83 mmol l(-1) +/- 0.27; and Cl(-), 171 mmol l(-1) +/- 20. Saccular endolymph concentrations were Na+, 166 mmol l(-1) +/- 22; K+, 51.4 mmol l(-1) +/- 16.7; Ca2+, 2.88 mmol l(-1) +/- 0.27; and Cl(-), 170 mmol l(-1) +/- 12; and semicircular canal (utricular vestibule) endolymph concentrations were Na+, 122 mmol l(-1) +/- 15; K+, 47.7 mmol l(-1) +/- 13.2; Ca2+, 1.78 mmol l(-1) +/- 0.48; Cl(-), 176 mmol l(-1) +/- 27. The relatively high concentrations of Ca2+ and Na+ in the endolymph may have significant implications for the physiological function of the mechanoelectrical transduction channels in the vestibular hair cells of fish compared to those of their mammalian counterparts.