Electric discharges and electrogenesis peculiarity in two African upside-down catfishes, <Emphasis Type="Italic">Synodontis caudovittatus</Emphasis> and <Emphasis Type="Italic">S. eupterus</Emphasis> (Mochokidae,Siluriformes)

The paper reports spontaneous generation of weak electric discharges with an amplitude of 0.4–1.0 mV and a frequency of 3–9 min^–1 by solitary Synodontis caudovittatus fish. When fish individuals were tested in pairs, their aggressive–defense interactions were associated with an increase in the amplitude of the discharges (up to 30–45 mV) compared to the discharges of individual fish, while the duration of the pulses increased up to 20–25 ms due to the prolongation of the second phase. In S. eupterus, electric activity was recorded only in the course of aggression–defense interactions, while spontaneous generation of discharges was not observed at all. The paper discusses the different aspects of electrocummunication between the catfish including the role of the reversion of polarity of the merged summated discharges with increased duration.     

Electrical Activity and Predation in the Clariid Catfish Clarias macrocephalus (Clariidae) Exposed to Varying Illumination

Journal of Ichthyology - The influence of illumination (light–dark) on electrical emission in a clariid catfish Clarias macrocephalus hunting fast-moving prey (guppies Poecilia reticulata)...     

The Duplex Nature of the Retina of the Nocturnal Gecko as Reflected in the Electroretinogram

The effect of light and dark adaptation on the electrical activity in two species of nocturnal gecko, Hemidactylus turcicus and Tarentola mauritanica was studied. The electroretinogram of both species changes from the scotopic type in the dark-adapted state to the photopic type after strong light adaptation. For the scotopic response fusion frequencies up to 18 flashes per sec. are obtained in both species. For the photopic response fusion frequencies up to 50 flashes per sec. are seen in Tarentola, and up to 25 flashes per sec. in Hemidactylus. Proceeding from dark to light adaptation the increment threshold (dI) is measured at different levels of adaptive illumination (I). At low levels of illumination the dI/I ratio is found to be small and at high levels of illumination to be large. No difference in the dI/I ratio is obtained for test lights of 462 and 605 mµ. During dark adaptation the change of threshold after exposure to moderate and weak lights (up to 10³ times dark threshold) is rather fast. After light adaptation to strong light (10⁶ times dark threshold) duplex dark adaptation curves are seen with a break separating a fast and a slow phase of dark adaptation. The significance of these results from a retina which possesses sense cells of only one type is discussed.     

Different kinetics of membrane potential formation in dark-adapted and preilluminated chloroplasts

The effects of varying dark interval on the kinetics of light-induced formation of the membrane potential were studied on individual chloroplasts of Anthoceros with the use of capillary microelectrodes. Illumination of the chloroplast with 1 s light pulse after 3 min dark period induced the photoelectrical response with two peaks of the potential that were located at 20 and 500 ms after the onset of illumination. The position of the second peak was shifted along the time-scale depending on the preceding dark interval. The repeated illumination of the chloroplast with 1 s light pulse after 30 s dark interval induced the electrical response with only one maximum and a monotonous decay of the potential in the light. Distinctions in the electrical responses induced by the first and the second light pulses were eliminated by the addition of 50 μM dicyclohexylcarbodiimide (DCCD). The results show that the photoinduction kinetics of the membrane potential in chloroplasts is affected by functioning of H⁺-ATPase. The delayed peak of the membrane potential in the photoinduction kinetics is interpreted as a consequence of the photoactivated electron transport supported by Photosystem I.     

Food- and light-entrainable oscillators control feeding and locomotor activity rhythms, respectively, in the Japanese catfish, Plotosus japonicus

Feeding and locomotor activities of the Japanese catfish Plotosus japonicus under solitary condition were recorded to identify mechanisms controlling these behaviours. In the absence of food, the catfish showed nocturnal locomotor activity, but no feeding activity. Under ad libitum food conditions, both feeding and locomotor activities occurred during the dark period and were synchronized with light/dark (LD) cycles. Feeding activity lasted for 11–24 days when food was stopped after ad libitum food availability. Restricted food during the light phase produced both food-anticipatory and light-entrainable feeding activity. Furthermore, this condition produced weak food-anticipatory and light-entrainable locomotor activity. Under the light/light (LL) condition, restricted food produced food-anticipatory feeding and locomotor activities, suggesting that a food-entrainable oscillator controls both feeding and locomotor activities. However, under the LL condition, light-entrainable feeding and locomotor activities were not observed, suggesting that a light-entrainable oscillator controls both feeding and locomotor activities. During a restricted food schedule, LD cycle shifts resulted in disrupted synchronization of feeding activity onset in three of the four fish, but one fish showed synchronized feeding activity. These results suggest that the food- and the light-entrainable oscillator may control feeding and locomotor activities, respectively.     

Visual cues during the alarm reaction of Gymnocharacinus bergi (Pisces, Characidae)

Gymnocharacinus bergi (Pisces, Characidae), an endemic fish in the headwaters of the Valcheta stream in northern Patagonia, displays a fright reaction. As this species inhabits a rapid stream, we hypothesized that the alarm reaction might be socially transmitted through visual information, because the detection of alarm pheromone would be restricted to those fish located downstream from the releaser. Alarm substances elicited a decrease in the swimming activity and a tendency to remain at the bottom of the aquarium. Individuals that observed the fright reaction, but were not exposed to the pheromone, spent significantly more time at the bottom of the aquarium imitating the alarm response, and tended to approach the others. Gregarious behaviour was observed; however, interactions (number of approaches) were stronger between those fish held prior to testing in the same aquarium; smaller fish in particular tended to get closer to bigger ones. Greater group cohesion was found between individuals that were exposed to the alarm pheromone.     

Episodic electric discharges in the course of social interactions: an example of Asian clariid catfish

Function of weak electric discharges is conclusively proved only for two fish orders - Mormyriformes and Gymnotiformes. Every specimen of the two groups emits electric discharges continuously or quite regularly for location, orientation and communication. The function of weak episodic electric discharges in other groups of weakly electric fish - Rajiformes, Uranoscopidae and Siluriformes, remains the puzzle since Darwin. Recent experiments made it possible to expand the list of weakly electric fish with episodic discharges. The range of behavioral situations accompanied with electric emission has been expanded as well. For instance, Asian catfish, Clarias macrocephalus, emit episodic discharges while in aggressive and spawning behavior. Asian catfish females emit the special burst of electrical discharges as a part of mating ritual. This burst cannot serve as an invitation to spawning or synchronization of reproductive products release, because females emit it after the sperm ejection. If females would need males' help for eggs release, it could be suggested that discharges assist in their mutual efforts. Since the electric field strength near fish is higher than fish's non-specialized electrical sensitivity thresholds, other hypotheses are possible. For example, it could be suggested that electric fields would make sperm or eggs more active. To proceed in our conception about episodic discharges function, new hardware and software are needed.     

Elaboration of equipment and methods of continuous recording of electric activity of clariid catfish (Clariidae,Siluriformes) in social and reproductive behavior

Equipment and methods of simultaneous continuous long-term recording of electric activity of clariid catfish (Clariidae) is elaborated. All electric organ discharges (EOD) in any position and orientation of free swimming fish are fixed by simultaneous recording of electric voltage with two mutually perpendicular pairs of electrodes. Light-emitting diodes controlled by a microprocessor allow for the possibility to observe the moments of discharge emission both in real time and during scanning of videorecords. According to its parameters, the created equipment corresponds to characteristics of EOD of clariid catfish, performs primary treatment of signals, and stores in its inner flash memory all discharges recorded in a prolonged experiment (duration up to several days, number of EOD up to several tens of thousands). Various examples of EOD are presented recorded by means of the elaborated methods in clariid catfish (C. macrocephalus, C. batrachus, C. fuscus, and hybrids C. gariepinus × C. macrocephalus) when they manifested aggressive-defensive and spawning behavior. The procedure of treatment of EOD is suggested, including that of special bursts of EODs generated by females in pairing.     

Characterization of an alarm pheromone secreted by amphibian tadpoles that induces behavioral inhibition and suppression of the neuroendocrine stress axis

Many species assess predation risk through chemical cues, but the tissue source, chemical nature, and mechanisms of production or action of these cues are often unknown. Amphibian tadpoles show rapid and sustained behavioral inhibition when exposed to chemical cues of predation. Here we show that an alarm pheromone is produced by ranid tadpole skin cells, is released into the medium via an active secretory process upon predator attack, and signals predator presence to conspecifics. The pheromone is composed of two components with distinct biophysical properties that must be combined to elicit the behavioral response. In addition to the behavioral response, exposure to the alarm pheromone caused rapid and strong suppression of the hypothalamo-pituitary-adrenal (HPA) axis, as evidenced by a time and dose-dependent decrease in whole body corticosterone content. Reversing the decline in endogenous corticosterone caused by exposure to the alarm pheromone through addition of corticosterone to the aquarium water (50 nM) partially blocked the anti-predator behavior, suggesting that the suppression of the HPA axis promotes the expression and maintenance of a behaviorally quiescent state. To our knowledge this is the first evidence for aquatic vertebrate prey actively secreting an alarm pheromone in response to predator attack. We also provide a neuroendocrine mechanism by which the behavioral inhibition caused by exposure to the alarm pheromone is maintained until the threat subsides.     

Antipredator responses to alarm pheromone in groups of young and/or old thrips larvae

Many prey species suffer from different predators in the course of their ontogeny. Hence, the alarm signal a small prey individual sends can have a different meaning than the signal a large prey individual sends, both for small and for large receivers. Larvae of Western Flower Thrips face predators that attack only small larvae, or predators that attack small larvae and large larvae. Furthermore, thrips larvae release a two‐component alarm pheromone, which varies in composition with larval age. Here, we study whether their response to alarm pheromone varies with composition of the pheromone. First, we confirmed that large and small larvae respond when nearby larvae of both sizes were prodded with a brush to induce alarm pheromone excretion. Subsequently, we tested whether thrips larvae of a given size respond differentially to alarm pheromone excreted by a small or large companion larva. We analyzed two types of behavior used in direct defense against a predator and one type of escape response. Only small (not large) larvae attempted to escape more frequently in response to excretions from a large larva. This difference in response could have been due to the alarm pheromone or to the companion larva in the vicinity. We subsequently tested for, but did not find, an effect of size of the companion larva on the behavior of the test larva when exposed to synthetic pheromone mimicking that of a large larva. Finally, we tested how pheromone composition affects antipredator behavior by exposing thrips larvae to synthetic pheromones differing in amount and ratio of the two components. Only for small larvae, we found significant changes in escape behavior with pheromone amount, and a trend with the ratio. Overall, we conclude that small thrips larvae respond differentially to alarm pheromones excreted by small and large larvae and that this differential response is due to differences in pheromone quantity and possibly also quality. Our results suggest that responses to alarm signals can vary with the chemical composition of those alarm signals.     

Influence of continuous light and darkness on the secretory pinealocytes of<Emphasis Type="Italic">Heteropneustes fossilis</Emphasis>

In an earlier study onHeteropneustes fossilis, evidence of secretory activity in the pinealocytes had been demonstrated at the electron microscopic (EM) level and it was found to exist in two phases: a secretory phase (light cells) and a storage phase (dark cells). In the present investigation,H. fossilis was subjected to artificial photoperiods of continuous illumination and continuous darkness for a period of ten days and the effect on the secretory pinealocytes was studied at the EM level. Marked results were observed within the short period of ten days emphasizing the role of environmental photoperiod on the secretory activity of the pinealocytes. During continuous illuminated phase, both light and dark cells were observed: the light cells showed intense secretory activity and dark cells a storage one. During the dark phase both types of cells were present but in different metabolic states and neither of the cells demonstrated synthetic nor storage activity. Light cells were metabolically active but not secretory active and dark cells showed a necrotic condition. Phagocytotic activity of the dark cells was also seen. Intense neural activity was also observed during exposure to both the artificial photoperiods. The results highlight the role of light on the secretory activities of the pinealocytes of the catfish pineal organ.     

The study of sensory bases of the feeding behavior of the African catfish Clarias gariepinus (Clariidae,Siluriformes)

An experimental study of the role of vision and some other sensory systems in the feeding behavior of the African catfish Clarias gariepinus (SL 20–24 cm, weight 80–95 g) was performed. It was shown that catfish similarly efficiently detect pellets of artificial food in the light and in the dark; in the dark, they display a greater preference for liver pieces than for pellets of artificial food of the same size. Blue pellets were most attractive for fish; red pellets, less attractive; and green pellets were the least attractive. Color selectivity is exhibited by catfish in the light at various combinations of pellets of different colors delivered simultaneously, but is lost in total darkness. The data obtained indicate the polysensory basis of the feeding behavior of catfish. In the light, a well-developed visual reception provides not only for a successful search for food, but also for a selective choice of food items by color. The olfactory and taste properties of food are important regulators of feeding under various light conditions. Thus, C. gariepinus, like other euryphagous fish, lacks a profound sensory specialization in the feeding behavior. When environmental conditions change, the role of the leading sensory system may pass from one sense organ to another.     

Phytochrome-mediated Carotenoids Biosynthesis in Ripening Tomatoes

Red light induced and far red light inhibited carotenoid biosynthesis in ripening tomatoes (Lycopersicon esculentum Mill.) when compared to controls kept in the dark. Red illumination following far red illumination reversed the inhibitory action of far red light on carotenoid biosynthesis, suggesting a phytochrome-mediated process. Quantitation of individual carotenoids favored the hypothesis of two separate carotenoid biosynthetic pathways in tomatoes.     

Day-night variations in plasma melatonin and arginine vasotocin concentrations in chronically cannulated flounder (Platichthys flesus).

Chronically catheterised, free swimming flounder (Platichthys flesus) have been used in experiments examining the day-night variations in circulating levels of melatonin (Mel) and arginine vasotocin (AVT). Under normal photoperiod (16 h light/8 h dark) serial blood samples taken from individual fish demonstrated a Mel rhythm with daytime levels at 09.00 and 15.00 h (238+/-14 and 179+/-12 fmol x ml(-1), respectively) lower than those at 23.00 h (1920+/-128 fmol x ml(-1)). Maintenance of fish in 24-h light abolished the light/dark Mel rhythm and circulating levels were comparable to those measured during the day in fish under normal photoperiod illumination. In fish maintained under 24 h dark, although a daily rhythm was still apparent, at the time when it would be normally dark, plasma Mel concentration was reduced and at times when it would be normally light, levels were higher than in fish maintained under normal light/dark illumination. Plasma AVT concentrations were higher in fish during the day (4.4+/-0.8 fmol x ml(-1)) than those at night (1.5+/-0.4 fmol x ml(-1)), the opposite to that seen with Mel. During acute study infusion of AVT resulted in reduced levels of plasma Mel, although this did not achieve statistical significance. Infusion of Mel did not alter circulating AVT concentration.     

Electrical discharges in Chinese salamander <Emphasis Type="Italic">Andrias davidianus</Emphasis>

In 2-year-old Chinese giant salamanders Andrias davidianus, occasional electric discharges with a characteristic pattern similar to the electric discharges of weakly electric catfish, Polypterus and Protopterus, were recorded for the first time. The discharges markedly differ in shape from the myograms accompanying abrupt movements of the salamander or exceeded them in amplitude by more than an order of magnitude. The discharges were recorded both in the autonomous experiment in the absence of experimenters and at a weak tactile stimulation.     

Locomotor activity rhythm in two wrasses,Halichoeres tenuispinnis andPteragogus flagellifera,under various light conditions

The locomotor activity rhythms were examined by using an actograph with infra-red photo-electric switches for two species of wrasses, (Halichoeres tenuispinnis andPteragogus flagellifera) under various light conditions. InH. tenuispinnis, the locomotor activity of almost all fish under light-dark cycle regimen (LD12:12; 06:00–18:00 light, 18:00–06:00 dark) commenced somewhat earlier than the beginning of light period and continued till somewhat earlier than the beginning of the dark period. This species clearly showed free-running activity rhythms under both constant illumination (LL) and constant darkness (DD). Therefore,H. tenuispinnis appeared to have a circadian rhythm. The length of the circadian period ranged from 23 hr. 30 min. to 23 hr. 44 min. under LL, and was from 23 hr. 39 min. to 24 hr. 18 min. under DD. On the other hand, the locomotor activity ofP. flagellifera occurred mostly in the light period under LD 12:12. The activity of this species continued through LL, but was greatly suppressed in DD, so that none of the fish had any activity rhythm in both constant conditions. It was known from field observations thatH. tenuispinnis burrowed and lay in sandy bottoms, whileP. flagellifera hid and rested in bases of seagrasses and shallow crevices of rocks during the night. In the present two wrasses, it seemed that the above-mentioned difference of noctural behavior was closely related to the intensity of the endogenous factor in the activity rhythm.     

Photoperiod cues and the modulatory action of octopamine and 5-hydroxytryptamine on locomotor and pheromone response in male gypsy moths,Lymantria dispar

Experiments were conducted to determine whether the biogenic amines octopamine (OA) and 5-hydroxytryptamine (5-HT) exert modulatory effects on pheromone responsiveness and random locomotor activity in male gypsy moths. When injected into males, OA significantly enhanced sensitivity to pheromone, while 5-HT enhanced general locomotor activity, results that were very similar to those previously shown for the cabbage looper. Maximal effect of the amines, however, was observed when injection occurred just prior to the onset of scotophase, rather than photophase, as we had originally hypothesized for this diurnally active insect. Male gypsy moths also displayed a prominent scotophase response, with sensitivity to pheromone greater in the scotphase compared with photophase, but with the level of random locomotor activity lower in scotophase than in photophase. The upwind flight behavior of males to a pheromone source in a wind tunnel, as well as the time spent at the source, were also significantly different in the two light regimes. Furthermore, when exposed to a 1 h scotophase (instead of the normal 8), or to continuous dark conditions, while males exhibited response to pheromone and locomotor activity during the same scotophase and photophase periods as observed in a 16:8 light : dark cycle, the levels of response, as well as qualitative aspects of the upwind flight behaviors in both periods were a function of the light intensity. Our combined results suggest that male gypsy moths display a bimodal rhythm of locomotor and pheromone response over the diel cycle, with light intensity and scotophase onset providing critical cues for the expression of behaviors, as well as the modulatory action of the amines. © 1992 Wiley-Liss, Inc.     

Conspecific and heterospecific alarm substance induces behavioral responses in piau fish Leporinus piau

In ostariophysan fish, the detection of alarm substance released from the skin of a conspecific or a sympatric heterospecific may elicit alarm reactions or antipredator behavioral responses. In this study, experiments were performed to characterize and quantify the behavioral response threshold of Leporinus piau, both individually and in schools, to growing dilutions of conspecific (CAS) and heterospecific skin extract (HAS). The predominant behavioral response to CAS stock stimulation was biphasic for fish held individually, with a brief initial period of rapid swimming followed by a longer period of immobility or reduced swimming activity. As the dilution of skin extract was increased, the occurrence and magnitude of the biphasic alarm response tended to decrease, replaced by a slowing of locomotion. Slowing was the most common antipredator behavior, observed in 62.5% of animals submitted to HAS stimulation. School cohesion, measured as proximity of fish to the center of the school, and swimming activity near the water surface significantly increased after exposure to CAS when compared with the control group exposed to distilled water. Histological analysis of the epidermis revealed the presence of Ostariophysi-like club cells. The presence of these cells and the behavioral responses to conspecific and heterospecific skin extract stimulation suggest the existence of a pheromone alarm system in L. piau similar to that in Ostariophysi, lending further support for the neural processing of chemosensory information in tropical freshwater fish.     

Photoregulation of Nicotinamide Adenine Dinucleotide Kinase Activity in Cell-free Extracts

This article gives evidence that NAD kinase activity is controlled by the action of phytochrome. The NADP level rapidly increased in the cotyledons of seedlings of Pharbitis nil strain Violet (a short day plant), when the inductive dark for flowering was interrupted with a 5-minute illumination of red light. Illumination with far red light immediately after illumination with red light counteracted partly the effect of the latter.     

Why do electric fishes swim backwards? An hypothesis based on gymnotiform foraging behavior interpreted through sensory constraints

Synopsis Fishes producing high-frequency wavelike electrical discharges maintain a relatively rigid body axis and swim forwards and backwards with equal ease. Using stop-action videotape filming we have observed the gymnotiform Apteronotus albifrons feeding on zooplankton and oligochaete annelids. Here it is reported that reverse swimming is characteristic of two foraging behaviors: searching for prey and assessing it. In assessing a potential prey item, fish typically scan it from tail to head by swimming backwards, then ingest it after a short forward lunge. A scan in the opposite direction-from head to tail by forward swimming-would have the prey located near the tail and out of position for the final lunge. Food choice experiments indicate that these electrosensing fish feed equally well, and take larger rather than smaller zooplankton, under light and dark conditions. Furthermore, electric fish take normal (light) colored and darkened prey (Daphnia) in a 50: 50 ratio under both dark and light conditions. These results are consistent with the interpretation that electrosensory cues are being used to detect zooplankton and other prey. Together, our observations support Lissmann's (1958, 1974) and Lissmann & Machin's (1958) assertion that backwards swimming is a component of a locomotory pattern guided by the constraints produced by an active electrical sense.