Feeding and associated electrical behavior of the Pacific electric ray Torpedo californica in the field

The predatory behavior of 74 Pacific electric rays (Torpedo californica), studied between August and December during 1988 through 1991 in situ off the Palos Verdes Peninsula, southern California, consisted of two feeding modes: an ambush from the substratum during the day and a more vigorous attack from the water column at night. Predatory motor patterns and electric organ discharges (EODs) were recorded on the video and audio channels of a housed camcorder. Predatory motor patterns included four phases: (1) jump (simultaneous with EOD initiation), (2) pectoral-fin cupping, (3) orientation to prey, and (4) ingestion. The initial electrical activity of the rays was a train of 46 to 414 5-ms monophasic EODs that lasted 0.45 to 7.06 s; the maximum number of EODs produced during an attack was >1200. Maximum output, measured on only one ray, was 45 V. Fifty-five rays were presented one of four types of prey stimuli: live fish (LF), freshly-speared fish (FSF), frozen fish (FF), or a simulated bioelectric field (SBF). The percent frequency of attacks for the LF, FSF, and FF treatments ranged from 70 to >90%, but was <30% for the SBF. The interval between prey presentation and attack was 30 s for the LF, FSF, and FF and over five times longer for the SBF; intervals averaged <4 s for the three rays tested at night. Attacks by rays on energized electrodes provide the first evidence that electric rays use electroreceptors to detect their prey. However, the lack of clear differences among the four prey treatments in five characteristics of the initial pulse train suggests that a suite of sensory stimuli cooperate in triggering an attack and regulating the electrical output during the attack.     

Comparison of liver mitochondrial membranes from an agnathan (Myxine glutinosa), an elasmobranch (Raja erinacea) and a teleost fish (Pleuronectes americanus)

The membranes of elasmobranch liver mitochondria differ substantially from those of other marine fish. Although the proportions of the major phospholipids in elasmobranch mitochondria are similar to those of other marine fish, there are considerable differences in the fatty acid content of the phospholipids. Specifically, the percentage of saturated fatty acids is much higher, the polyunsaturated fatty acid content is much lower and the chain length is shorter than is typical of other non-urea retaining fishes. The tissues of elasmobranch fishes are unusual in that they contain the chaotropic agent urea at levels that are capable of disrupting the hydrophobic interactions responsible for membrane integrity. The mitochondrial membrane properties of the elasmobranch are consistent with those needed to maintain membrane integrity in the presence of physiological amounts of urea and indicate membrane adaptation to urea. Present address: INRS eau 2800 Rue Einstein, suite 105 Case Postale, 7500, Sainte Foy, Quebec G1V 4C7 Canada     

Third-stage larva shifts host fish from teleost to elasmobranch in the temporary parasitic isopod, Gnathia trimaculata (Crustacea; Gnathiidae)

The life cycle of the fish ectoparasitic isopod Gnathia trimaculata is described based on both field samplings and laboratory observations. Species identification of the larvae was based on morphological observation and supported by molecular analysis. As the results of field samplings in several sites of southwestern and central Japan (24–34°N, 124–139°E) from 2005–2011, approximately 900 third-stage larvae of G. trimaculata were found on 25 elasmobranch species, and 220 first- and second-stage larvae were found on three teleost species. No third-stage larvae were found on the teleosts, and the larvae of younger stages never infested elasmobranchs. Therefore, G. trimaculata is supposed to shift its host from teleosts to elasmobranchs as it develops. We discuss the developmental periods, life span, distribution, and predation risk of the present species compared with other gnathiid species.     

Comparison of in vitro characteristics of and experimental lesions produced by a clinical and an environmental isolate of Aspergillus flavus

In the present study, two strains of Aspergillus flavus (one from a human corneal ulcer and one from the environment) were found to be strikingly similar in vitro in terms of thermotolerance, inability to grow in an anaerobic environment and in secreting proteinases; however, one obvious difference was that the clinical isolate produced 120 ppb of aflatoxin B1 in glucose salt medium while the environmental isolate did not produce this toxic metabolite. Alterations in the activities of acid phosphatase (ACP), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and glutathione-S-transferase were observed in the liver, kidney and serum in an experimental rat model, irrespective of whether the animal had been challenged with the clinical isolate or the environmental isolate of A. flavus. In rats that had been challenged with the clinical isolate, a significant decrease in the activity of kidney ALP was noted, whereas in rats that had been challenged with the environmental isolate, the reverse was observed. While these differential alterations may have occurred due to differences in the toxin-producing ability of the two isolates, further investigation is warranted to clarify whether other phenotypic, or genotypic, differences are also involved.     

Female discharges are more electrifying: spontaneous preference in the electric fish,Eigenmannia (Gymnotiformes,Teleostei)

Summary The tropical South American teleost Eigenmannia lineata showed a spontaneous preference for the female type, compared with the male type, of its sexually dimorphic, weak-electric organ discharge (EOD). Female and male EODs differ in waveform and harmonic content. An isolated fish was simultaneously stimulated with digitally synthesized natural male and female EODs of equal peak-to-peak amplitudes, at ±35 Hz frequency difference centered on its stable resting discharge frequency. The stimulus dipoles were arranged symmetrically to the right and left of the fish's hiding place. All stimulus conditions were permuted at random sequence. Among 11 fish tested, 8 showed a statistically significant preference for one stimulus, the female type, as measured by the amount of time a fish spent close to a stimulus dipole (P<0.05 in each fish, two-tailed). Thus female EODs rather than male EODs were more attractive to adult and juvenile fish of both sexes. It was also concluded that E. lineata is capable of discriminating female from male EODs by a complex sensory capacity requiring neither amplitude nor frequency cues. The EOD waveform changed very little within the ecological range of water conductivities (approximately 10–100 S·cm^-1); the P/N-ratio (a waveform character based on zerocrossing intervals) depended only weakly, but significantly, on conductivity (negative correlation in all four fish). Also, the effect of temperature on EOD waveform was very weak: Q ₁₀-values of the P/N-ratio were below but close to 1 in all fish (27±5°C). Thus, it can be concluded that the EOD waveform is remarkably stable within widely changing conditions-even beyond the variation found in the field-and is therefore potentially useful as a social cue.     

Seasonal variations in the densities of fecal pellets produced by Oikopleura vanhoeffeni (C. Larvacea) and Calanus finmarchicus (C. Copepoda)

Two abundant macrozooplankters, Oikopleura vanhoeffeni (Lohmann) and Calanus finmarchicus (Gunnerus) were collected from the coastal waters off Newfoundland in different seasons during 1990–1991 and incubated in natural seawater to collect freshly egested, field produced, fecal pellets. The densities of fecal pellets from O. vanhoeffeni and C. finmarchicus were measured in an isosmotic density gradient. These are the first reported seasonal measurements of fecal pellet densities from two different types of macrozooplankters, O. vanhoeffeni, a larvacean, filter feeder and C. finmarchicus, a crustacean, suspension feeder. Pellet density ranges and medians were significantly different among seasons for both species, depending primarily on the type of phytoplankton ingested and its ability to be compacted. Winter O. vanhoeffeni and fall C. finmarchicus feces filled with nanoplankters and soft bodied organisms had less open space [packing index (% open area) = 3.5 and 4% for O. vanhoeffeni and C. finmarchicus, respectively] and were more dense (1.23 and 1.19 g cm^-3) than spring feces filled with diatoms (packing index = 15 and 23%, density = 1.13 and 1.11 gcm^-3). For copepods, these results contrast with previously published density values and with the predicted copepod fecal pellet density calculated, in the present study, using the conventional mass/volume relationship. Copepod spring and summer diatom-filled feces had a calculated density of 1.12 and 1.24 gcm^-3 vs a measured median density of 1.11 gcm^-3 for both spring and summer feces; the fall feces containing nanoplankters had a calculated density of 1.08 gcm^-3 vs a measured median density of 1.19 gcm^-3. Knowledge of the seasonal variations in fecal pellet densities is important for the development of flux models.     

Importance of cysts in the population dynamics of the red tide flagellate Heterosigma akashiwo (Raphidophyceae)

To elucidate roles of cysts in occurrences of Heterosigma akashiwo blooms, cyst dynamics were studied in northern Hiroshima Bay, the Seto Inland Sea of Japan, where H. akashiwo regularly forms red tide in June. Monthly measurements of seasonal changes in the densities of vegetative cells of H. akashiwo and their germinable cysts in surface sediments (top 1-cm layer) were made for 2 years at three stations. Vegetative cells of H. akashiwo could be detected from April through December throughout the water column, and the existence of vegetative cells was confirmed in surface waters even in winter after incubation of sampled seawater in culture medium. Germinable cysts, enumerated by the extinction dilution method, existed in sediments in all seasons, even before and after the seasonal bloom. The effects of incubation temperature on the germination of natural cysts of H. akashiwo in sediments were examined. Germination was not observed at 5 °C, was low at 10 °C, while it increased at 15 °C, and maintained a high level to 25 °C. The bottom water temperature reached 15 °C (suitable for the germination of cysts) and the surface about 18 °C or more (suitable for the growth of vegetative cells) 2 to 3 weeks before the blooms. The dark survival of H. akashiwo cysts was tested, and it was found that the cysts were viable for at least 650 d at 11 °C, and for 165 d at 25 °C, indicating a significant role of cysts in the survival during winter and summer seasons. The cysts presumably also play an important role in seeding primary populations into water columns when the bottom water reaches a suitable temperature (around 15 °C); thereafter the populations develop with great annual regularity to bloom in June. These results suggest that initiation of H. akashiwo red tides in the Seto Inland Sea could be triggered by bottom water temperature. Received: 3 July 1998 / Accepted: 12 January 1999     

Electrosensory prey detection in the African sharptooth catfish, Clarias gariepinus (Clariidae), of a weakly electric mormyrid fish, the bulldog (Marcusenius macrolepidotus)

During their seasonal runs in the Okavango and other freshwater bodies in southern Africa, the sharptooth catfish, Clarias gariepinus, specialises on the bulldog, Marcusenius macrolepidotus, as its main prey. We examined whether the catfish can locate bulldogs by detecting their pulse-type electric organ discharges (EODs). The electrosensory threshold for single-cycle, monopolar square-wave pulses was exceedingly low (down to 13 μV_p–p/cm for 4-ms pulses) in trained, food-rewarded sharptooth catfish (n=4), confirming the results of Lissmann and Machin who were, however, unable to identify a biological function. Other stimulus pulse waveforms (single-cycle, monopolar as well as bipolar sine-wave pulses) were also effective stimuli according to their spectral low-frequency energy contents (0– 30 Hz). Male bulldogs display an EOD pulse approximately 10× the duration of female EODs (≈0.5 ms). The C. gariepinus threshold for field-recorded playbacks of a male bulldog EOD (of long duration) was 103 μV_p–p/cm, whereas the brief female and juvenile EODs were not detected (using intensities of natural EODs). EODs of other mormyrids were detected when either monopolar or of long duration. Signal source amplitude increased linearly with standard length (SL) in bulldogs. Signal reach, as calculated from signal source amplitude and receiver sensitivity, is up to 150 cm for a large male bulldog (SL 27.5 cm), and 83 cm for a male that has just turned sexually mature (SL 12.6 cm). Therefore, most bulldogs eaten by catfish are probably male, in agreement with the size distribution of bulldogs found in catfish stomachs. These results suggest that sharptooth catfish rely heavily on their acute electrical sense during hunting, and an important function for electroreception in an African catfish has been identified. Received: 13 December 1999 / Revised: 20 April 2000 / Accepted: 20 May 2000     

Potential application of sludge produced from coal mine drainage treatment for removing Zn(II) in an aqueous phase

Various analyses of physico-chemical characteristics and batch tests were conducted with the sludge obtained from a full-scale electrolysis facility for treating coal mine drainage in order to find the applicability of sludge as a material for removing Zn(II) in an aqueous phase. The physico-chemical analysis results indicated that coal mine drainage sludge (CMDS) had a high specific surface area and also satisfied the standard of toxicity characteristic leaching procedure (TCLP) because the extracted concentrations of certain toxic elements such as Pb, Cu, As, Hg, Zn, and Ni were much less than their regulatory limits. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the CMDS mainly consists of goethite (70%) and calcite (30%) as a weight basis. However, the zeta potential analysis represented that the CMDS had a lower isoelectric point of pH (pH(IEP)) than that of goethite or calcite. This might have been caused by the complexation of negatively charged anions, especially sulfate, which usually exists with a high concentration in coal mine drainage. The results of Fourier transform infrared (FT-IR) spectrometry analysis revealed that Zn(II) was dominantly removed as a form of precipitation by calcite, such as smithsonite [ZnCO?] or hydrozincite [Zn?(CO?)?(OH)?]. Recycling sludge, originally a waste material, for the removal process of Zn(II), as well as other heavy metals, could be beneficial due to its high and speedy removal capability and low economic costs.     

Potential application of sludge produced from coal mine drainage treatment for removing Zn(II) in an aqueous phase

Various analyses of physico-chemical characteristics and batch tests were conducted with the sludge obtained from a full-scale electrolysis facility for treating coal mine drainage in order to find the applicability of sludge as a material for removing Zn(II) in an aqueous phase. The physico-chemical analysis results indicated that coal mine drainage sludge (CMDS) had a high specific surface area and also satisfied the standard of toxicity characteristic leaching procedure (TCLP) because the extracted concentrations of certain toxic elements such as Pb, Cu, As, Hg, Zn, and Ni were much less than their regulatory limits. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the CMDS mainly consists of goethite (70%) and calcite (30%) as a weight basis. However, the zeta potential analysis represented that the CMDS had a lower isoelectric point of pH (pH_IEP) than that of goethite or calcite. This might have been caused by the complexation of negatively charged anions, especially sulfate, which usually exists with a high concentration in coal mine drainage. The results of Fourier transform infrared (FT-IR) spectrometry analysis revealed that Zn(II) was dominantly removed as a form of precipitation by calcite, such as smithsonite [ZnCO₃] or hydrozincite [Zn₅(CO₃)₂(OH)₆]. Recycling sludge, originally a waste material, for the removal process of Zn(II), as well as other heavy metals, could be beneficial due to its high and speedy removal capability and low economic costs.     

The role of cysts on population dynamics of Scrippsiella spp. (Dinophyceae) in Onagawa Bay,northeast Japan

The seasonal behavior of both vegetative cells and cysts of dinophytes Scrippsiella spp., mostly S. trochoidea, which is the dominant group among dinoflagellate populations in Onagawa Bay on the northeastern coast of Honshu, Japan, was investigated between 1990 and 1992. The germination of the cysts after 8 d incubation under favorable laboratory conditions was examined using the extinction dilution method. Incessant germination occurred throughout the year, but the germination ratio (no. of germinable cysts/total cysts) varied seasonally with a marked fluctuation during summer when vegetative cells in the water column were abundant. Although such fluctuation largely reflects the variable flux of newly deposited immature cysts produced by the vegetative cells, the regulation of germination caused by a lowered saturation of dissolved oxygen (DO) under thermally stratified conditions was also suggested. During winter, while the cysts germinated in the laboratory, vegetative cells were not found in the water column. These facts suggest that germination in situ is regulated by low temperature in winter and possibly by lowered DO and by cyst age as well in summer. Such regulation prevents simultaneous germination of all the cysts, which is disadvantageous for the population because it would be more difficult to survive adverse conditions such as successive nutrient depletion and higher grazing risk.     

Estimation of the amount of dry deposition in an urban area (Kobe city, Japan) by the inferential method

The amount of dry deposition of SO₂(g) and HNO₃(g) in an urban area in Japan has been estimated by the inferential method. The mean annual dry deposition of SO₂(g) (2.91 kgS/ha/year) was close to or less than that in the Clean Air Status and Trends Network (CASTNet) of the U.S. (3.59 kgS/ha/year). The mean annual dry deposition of HNO₃(g) (10.8 kgN/ha/year) was approximately six times larger than that in CASTNet (1.85 kgN/ha/year). The proportions of dry/(dry+wet) deposition for sulfur and nitrogen were 0.301 and 0.785, respectively.     

Effects of grazing by two species of sea urchins (Strongylocentrotus franciscanus and Lytechinus anamesus) on recruitment and survival of two species of kelp (Macrocystis pyrifera and Pterygophora californica)

We studied the effects of grazing by two species of sea urchins on two species of kelp (Macrocystis pyrifera and Pterygophora californica) in the San Onofre kelp bed in southern California from 1978 through 1981. Both red sea urchins, Strongylocentrotus franciscanus, and white sea urchins, Lytechinus anamesus, were abundant and lived in aggregations. The purple sea urchin (S. purpuratus) was rare at the study site and was not studied. The aggregations of red urchins were either relatively small and stationary (for over 3 yr) or relatively large and motile (advancing at about 2 m mo^–1). Both stationary and moving aggregations were observed at the same time, and within 100 m of one another. Stationary aggregations of red urchins probably subsisted mainly on drift kelp and had no effect on kelp recruitment or on adult kelp abundance. In contrast, red sea urchins in large, motile aggregations or fronts ate almost all the macroalgae in their path. The condition of their gonalds indicated that red urchins in fronts were starved relative to red urchins in the small, stationary aggregations. Large, motile aggregations developed after 2 yr of declining kelp abundance (probably due largely to storms). We propose that a scarcity of drift algae for food results in a change in the behavior pattern of the red urchins and thus leads to the formation of large, motile aggregations. The aggregations of white urchins, which occurred along the offshore margin of the kelp bed, were large, but relatively stationary. The white urchins rarely ate adult kelps, but grazed extensively on early developmental stages of kelps and evidently prevented seaward expansion of the bed. The spatial distribution of both types of red urchin aggregations appeared to be unrelated to predation pressure from fishes or lobsters.Please address all requests for reprints to the senior author at his present address.     

Ultrastructure and behavior of the larva of Phragmatopoma californica (Polychaeta: Sabellariidae): identification of sensory organs potentially involved in substrate selection

The tentacles of the larvae of Phragmatopoma californica (Fewkes) a tubicolous, reef-building polychaete, were examined by video-equipped light microscopy and transmission and scanning electron microscopy. The surface of the tentacles has a unique ciliation pattern, consisting of dorsal tufts of short immotile cilia, ventrolateral tufts of short and long immotile cilia, and ventral motile cilia. Cells bearing immotile cilia are primary sensory cells with long basal processes that form synapses with basiepithelial nerve fibers. The sensory cell cytoplasm is similar to that of nervous tissue, and contains microtubules, neurofilaments, and synaptic vesicles. Sensory cell synapses with basiepithelial nerves appear to be both axodendritic and axoaxonic. The structure of the immotile cilia is compared to that of motile cilia. Unlike motile cilia, immotile cilia are short, rigid, end in a blunt tip and possess and axoneme with typically arranged mictotubules that terminate in an electron-dense end plate. The basal feet of immotile cilia do not anastomose with adjacent basal bodies, and the ciliary membrane is loosely applied to the axoneme and is covered by a surface coat of filamentous material. The use of the larval tentacles during substrate exploration, and the location and ultrastructure of sensory cilia, indicate that they may be involved in the perception of substrateassociated chemical signals and/or mechanical cues of significance in substrate selection.