Opercular Activity and Temporal Organization of Surfacing Behaviour in Indian Catfishes,Clarias batrachus and Heteropneustes fossilis

Opercular and surfacing activity were observed in the Indian catfish Clarias batrachus and Heteropneustes fossilis. In the series A experiments, the opercular activity was monitored under two experimental conditions, viz., (1) surfacing allowed and (2) surfacing prevented. A statistically significant elevation of the rate of opercular activity was observed when air breathing was prevented in both species. In addition, a significant prevention effect and a time of day dependence of that were noticed in both species. In the series B experiments, temporal patterns of surfacing and air-gulping activities were examined under an artificial LD 12:12 schedule at 2-h intervals over a period of 48 h. The inter air-gulping interval in minutes between two consecutive bouts was also recorded four times each day in both species. A significant 24-h rhythm was found for the rate of surfacing activity and length of the inter air-gulping interval in both species. However, the overall activity appears to be much higher in Heteropneustes fossilis as compared to Clarias batrachus.     

Inter-specific hybridization between freshwater catfish Mystus cavasius (Ham & Buch) and M. seenghala (Sykes) by artificial fertilization

By employing the technique of induced ovulation for artificial fertilization, inter-specific hybrids between the threatened catfish species (Mystus cavasius x M. seenghala) were produced. Fertilization, hatching and survival were significantly different between control and hybrids. The hatching time of the hybrid was significantly lower than that of the control. The average performance viz., hatching time and viability of larvae of the control fish, was significantly better than that of the hybrids. In the hybrid cross, hatchlings were mostly deformed and abnormal and after yolk absorption ultimately succumbed.     

Opercular Activity and Temporal Organization of Surfacing Behaviour in Indian Catfishes, Clarias batrachus and Heteropneustes fossilis

Opercular and surfacing activity were observed in the Indian catfish Clarias batrachus and Heteropneustes fossilis . In the series A experiments, the opercular activity was monitored under two experimental conditions, viz., (1) surfacing allowed and (2) surfacing prevented. A statistically significant elevation of the rate of opercular activity was observed when air breathing was prevented in both species. In addition, a significant prevention effect and a time of day dependence of that were noticed in both species. In the series B experiments, temporal patterns of surfacing and air-gulping activities were examined under an artificial LD 12:12 schedule at 2-h intervals over a period of 48 h. The inter air-gulping interval in minutes between two consecutive bouts was also recorded four times each day in both species. A significant 24-h rhythm was found for the rate of surfacing activity and length of the inter air-gulping interval in both species. However, the overall activity appears to be much higher in Heteropneustes fossilis as compared to Clarias batrachus .     

Annual Cycle of Thermal Tolerance in Sham-Pinealectomized and Pinealectomized Air-Breathing Catfish Clarias batrachus

Annual variations in thermal tolerance and the influence of the pineal there on were investigated in the ectotherm, Clarias batrachus, exposed to natural photothermal conditions in the laboratory. Thermal tolerance was assayed by measuring the critical thermal maximum (CTM) in sham-pinealectomized and pinealectomized animals every month for 1 year. A pronounced annual rhythm of thermal tolerance was validated, with the maximum recorded during the spawning phase and the minimum during the resting phase of the annual reproductive cycle of the catfish. This may have an adaptive significance since, during the spawning period, the fish ventures to nearby inundated areas, even going over a land route. An elevation in CTM will thus allow the “walking” catfish to better exploit the environment. Pinealectomy did not have any significant effect on the annual rhythm in thermal tolerance.     

Seasonal effects of pinealectomy on testicular recrudescence and secretory activity of seminal vesicles in the catfish Heteropneustes fossilis (Bloch)

The effects of pinealectomy on testicular activity and secretory activity of seminal vesicles were examined in the catfish Heteropneustes fossilis under various combinations of photoperiod and temperature during different periods of the annual reproductive cycle. Pinealectomy had no effect on gonadal activity during the preparatory, prespawning and spawning periods of the reproductive cycle. However, during the postspawning period, under long (LD 14:10) or short (LD 9:15) photoperiod at 25° C or at gradually increasing ambient temperature, pinealectomy accelerated testicular recrudescence and secretory activity of the seminal vesicles. Nevertheless. during this period the presence of the pineal facilitated the recrudescence of testes and seminal vesicles in catfish exposed to continuous light (LL), continuous darkness (DD) and 12 hL:l2 hD (LD) at 25° C. These findings suggest that the role of the pineal in catfish reproduction is variable and depends upon the photoperiod and temperature regimes to which the fish are exposed, as well as on the time of the year and the state of the reproductive cycle. The results also suggest that the effects of pinealectomy in catfish are mediated through an influence on the hypothalamo-hypophyseal gonadal axis.     

Annual Cycle of Thermal Tolerance in Sham-Pinealectomized and Pinealectomized Air-Breathing Catfish Clarias batrachus

Annual variations in thermal tolerance and the influence of the pineal there on were investigated in the ectotherm, Clarias batrachus , exposed to natural photothermal conditions in the laboratory. Thermal tolerance was assayed by measuring the critical thermal maximum (CTM) in sham-pinealectomized and pinealectomized animals every month for 1 year. A pronounced annual rhythm of thermal tolerance was validated, with the maximum recorded during the spawning phase and the minimum during the resting phase of the annual reproductive cycle of the catfish. This may have an adaptive significance since, during the spawning period, the fish ventures to nearby inundated areas, even going over a land route. An elevation in CTM will thus allow the “walking” catfish to better exploit the environment. Pinealectomy did not have any significant effect on the annual rhythm in thermal tolerance.     

Comparative analyses of the pigment-aggregating and -dispersing actions of MCH on fish chromatophores

In melanophores of the peppered catfish and the Nile tilapia, melanin-concentrating hormone (MCH) at low doses (<1 μM) induced pigment aggregation, and the aggregated state was maintained in the presence of MCH. However, at higher MCH concentrations (such as 1 and 10 μM), pigment aggregation was immediately followed by some re-dispersion, even in the continued presence of MCH, which led to an apparent decrease in aggregation. This pigment-dispersing activity at higher concentrations of MCH required extracellular Ca²⁺ ions. By contrast, medaka melanophores responded to MCH only by pigment aggregation, even at the highest concentration employed (10 μM). Since it is known that medaka melanophores possess specific receptors for α-melanophore-stimulating hormone (α-MSH), the possibility that interaction between MSH receptors and MCH at high doses in the presence of Ca²⁺ might cause pigment dispersion is ruled out. Cyclic MCH analogs, MCH (1–14) and MCH (5–17), failed to induce pigment dispersion, whereas they induced aggregation of melanin granules. These results suggest that another type of MCH receptor that mediates pigment dispersion is present in catfish and tilapia melanophores, and that intact MCH may be the only molecule that can bind to these receptors. Determinations of cAMP content in melanophores, which were isolated from the skin of three fish species and treated with 10 nM or 10 μM MCH, indicate that MCH receptors mediating aggregation may be coupled with Gi protein, whereas MCH receptors that mediate dispersion may be linked to Gs. The response of erythrophores, xanthophores and leucophores to MCH at various concentrations was also examined, and the results suggest that the distribution patterns of the two types of MCH receptors may differ among fish species and among types of chromatophore in the same fish.     

The relative impacts of native and introduced predatory fish on a temporary wetland tadpole assemblage

Understanding the relative impacts of predators on prey may improve the ability to predict the effects of predator composition changes on prey assemblages. We experimentally examined the relative impact of native and introduced predatory fish on a temporary wetland amphibian assemblage to determine whether these predators exert distinct (unique or non-substitutable) or equivalent (similar) impacts on prey. Predatory fish included the eastern mosquitofish (Gambusia holbrooki), golden topminnow (Fundulus chrysotus), flagfish ( Jordanella floridae), and the introduced walking catfish ( Clarias batrachus). The tadpole assemblage included four common species known to co-occur in temporary wetlands in south-central Florida, USA: the oak toad (Bufo quercicus), pinewoods treefrog (Hyla femoralis), squirrel treefrog (Hyla squirella), and eastern narrowmouth toad (Gastrophryne carolinensis). Tadpoles were exposed to different predators in wading pools under conditions similar to those found in surrounding temporary wetlands (particularly in terms of substrate type, the degree of habitat complexity, and temperature). Native predators were similar with respect to predation rate and prey selectivity, suggesting similar energy requirements and foraging behavior. Conversely, native fish predators, especially G. holbrooki, were distinct from the introduced C. batrachus. In contrast to expectations, C. batrachus were less voracious predators than native fish, particularly G. holbrooki. Moreover, survival of G. carolinensis and H. femoralis were higher in the presence of C. batrachus than G. holbrooki. We suggest that C. batrachus was a less efficient predator than native fish because the foraging behavior of this species resulted in low predator-prey encounter rates, and thus predation rate. In combination with a related field study, our results suggest that native predatory fish play a stronger role than C. batrachus in influencing the spatial distribution and abundance of temporary wetland amphibians in the landscape.     

A comparative survey of the type of sympathetic neuro-melanophore transmission in catfishes

The types of innervation to integumental melanophores were surveyed comparatively within the order Siluriformes. In fish or many families, pigment aggregation within melanophores was found to be under the control of adrenergic sympathetic postganglionic fibers as in other fish. In silurid catfish, on the other hand, the cells were found to be regulated cholinergically, though the fibers concerned were sympathetic postganglionic. Muscarinic cholinoceptors mediate the melanin-aggregating response. In some catfish belonging to Bagridae, Pimelodidae and Callichthyidae, the melanophores strangely possessed cholinoceptors, notwithstanding the fact that they were under adrenergic nervous control. These results were discussed in conjunction with the phylogeny of Siluriformes.     

Effects of the Pineal and Melatonin, With or Without Inhibitors of Thyroid Hormone/Testosterone, on Total Protein Contents of Serum, Liver and Muscle Tissues of Clarias batrachus during Different Phases of its Annual Gonadal Cycle

Studies were planned to elucidate if the pineal plays any part in the regulation of protein contents in the serum and tissues of an Indian freshwater catfish, Clarias batrachus . In addition, an attempt has been made to investigate the modulatory roles of the status of thyroid and testis by using two potent inhibitors, i.e. iopanoic acid (thyroid inhibitor) and cyproterone acetate (androgen inhibitor). The results suggest that in general, the effects of the pineal and melatonin on protein content of serum and muscle and liver tissues are mediated with the involvement of the gonads. In addition, the thyroid status modulated the effects of pinealectomy on liver and muscle protein.     

Perturbations in the catfish immune responses by arsenic: organ and cell specific effects

The present study was an attempt to elucidate the effect of non-lethal arsenic (As) exposure (1/10 LC50) on different immunologically important organs and cells of a catfish. Clarias batrachus L. were exposed to arsenic trioxide for different time intervals, which resulted in significant, time-dependent changes in total head kidney and splenic leucocyte count (p<0.05) and reduction in the organosomatic indices (p<0.05) of these two important immunocompetent organs. Routine histological studies revealed arsenic induced changes in the cellular composition of head kidney and spleen. Arsenic also induced time-dependent and tissue-specific alterations in T and B cell functioning in catfish. When checked for its effects on macrophages, it was noted that arsenic interfered with bacterial phagocytosis. Furthermore, arsenic affected the general immune status of C. batrachus and rendered the fish immunocompromised and susceptible to pathogens.     

Effects of the Pineal and Melatonin,With or Without Inhibitors of Thyroid Hormone/Testosterone,on Total Protein Contents of Serum,Liver and Muscle Tissues of Clarias batrachus during Different Phases of its Annual Gonadal Cycle

Studies were planned to elucidate if the pineal plays any part in the regulation of protein contents in the serum and tissues of an Indian freshwater catfish, Clarias batrachus. In addition, an attempt has been made to investigate the modulatory roles of the status of thyroid and testis by using two potent inhibitors, i.e. iopanoic acid (thyroid inhibitor) and cyproterone acetate (androgen inhibitor). The results suggest that in general, the effects of the pineal and melatonin on protein content of serum and muscle and liver tissues are mediated with the involvement of the gonads. In addition, the thyroid status modulated the effects of pinealectomy on liver and muscle protein.     

Pharmacological Profiles of the Subtypes of Muscarinic Cholinoceptors That Mediate Aggregation of Pigment in the Melanophores of Two Species of Catfish

Using selective antagonists, including pirenzepine, adiphenine, AF-DX116, gallamine, and 4-DAMP we attempted to characterize the muscarinic cholinoceptors on the melanophores of the translucent glass catfish Kryptopterus bicirrhis and the mailed catfish Corydoras paleatus. The M₃ receptor-selective antagonist, 4-DAMP, potently inhibited the acetylcholine-induced aggregation of pigment in both species. It appeared, therefore, that the receptors that mediated the cholinergically evoked aggregation of melanosomes in these species were of the M₃ muscarinic subtype.     

Effect of alkalinity (pH 10) on ureogenesis in the air-breathing walking catfish,Clarias batrachus

Exposure of fish to alkaline conditions inhibits the rate of ammonia excretion, leading to ammonia accumulation and toxicity. The purpose of this study was to determine the role of ureogenesis via the urea cycle, to avoid the accumulation of ammonia to a toxic level during chronic exposure to alkaline conditions, for the air-breathing walking catfish, Clarias batrachus, where a full complement of urea cycle enzyme activity has been documented. The walking catfish can survive in water with a pH up to 10. At a pH of 10 the ammonia excretion rate by the walking catfish decreased by approximately 75% within 6 h. Although there was a gradual improvement of ammonia excretion rate by the alkaline-exposed fish, the rate remained 50% lower, even after 7 days. This decrease of ammonia excretion was accompanied by a significant accumulation of ammonia in plasma and body tissues (except in the brain). Urea-N excretion for alkaline-exposed fish increased 2.5-fold within the first day, which was maintained until day 3 and was then followed by a slight decrease to maintain a 2-fold increase in the urea-N excretion rate, even after 7 days. There was also a higher accumulation of urea in plasma and other body tissues (liver, kidney, muscle and brain). The activity of glutamine synthetase and three enzymes operating in the urea cycle (carbamyl phosphate synthetase, argininosuccinate synthetase, argininosuccinate lyase) increased significantly in hepatic and extra-hepatic tissue, such as the kidney and muscle in C. batrachus, during exposure to alkaline water. A significant increase in plasma lactate concentration noticed during alkaline exposure possibly helped in the maintenance of the acid-base balance. It is apparent that the stimulation of ureogenesis via the induced urea cycle is one of the major physiological strategies adopted by the walking catfish (C. batrachus) during chronic exposure to alkaline water, to avoid the in vivo accumulation of ammonia to a toxic level in body tissues and for the maintenance of pH homeostasis.     

Photoresponse ontogeny and its relation to development of pineal organ and eye in larval bagrid catfish Mystus nemurus (Valenciennes)

The artificially reared bagrid catfish Mystus nemurus was observed for the histological development of the pineal organ and retina and photoresponse in a test tank at hatching to 14?d after hatching. The pineal organ was functional at hatching, and the lens-like tissue was partly ossified forming a pineal window at 6?d. The retina became morphologically functional when the outer segments of single cones were formed, and the eyes were innervated with the optic tectum at 18?h and rods were formed at 36?h. Long and thin single cones were not observed. The larvae exhibited undirected kinetic movement at hatching to 12?h and directed tactic swimming away from a torch after 18?h in response to a torch light. The photoresponse of the larvae was negative at hatching to 30?h and at 6?d to the end of the observation at 14?d, but neutral during a period at 36?h to 5?d. It was evident that the kinetic movement was mediated by light perception with the pineal organ, which was not capable of detecting directed signal information, and that the larvae were capable of directed tactic movement only when vision was involved. The vigorous negative phototaxis at 6–14?d was attributed to the improvement of photosensitivity of the retina and the pineal organ.     

Induction of morphogenically competent callus and suspension cell cultures from leaf explants and mature seeds ofDigitaria sanguinalis

Summary Digitaria sanguinalis (crabgrass) has recently been introduced as a high quality forage crop. We report here a tissue culture system showing a high level of regeneration developed to aid in a breeding program. Two morphologically distinct types of callus, compact opaque and friable translucent, were induced from leaf blade explants and mature seeds when cultured on MS medium containing 0.9 μM 2,4-dichlorophenoxyacetic acid. Proline (25 mM) inhibited induction of callus but was required for continued maintenance. Plants were readily regenerated from the compact opaque callus. Selectively subcultured friable translucent callus continued to produce colony sectors of the morphogenically competent compact opaque callus when transferred to regeneration medium. Suspension cell cultures derived from callus or directly from leaf blade explants also produced regenerable callus.     

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.     

Alpha1 and alpha2 adrenoceptor mediated melanosome aggregatory responses in vitro in Oreochromis mossambica (Peters) melanophores

Effects of specific and non-specific adrenoceptor agonists and antagonists were examined on the isolated scale melanophores of O. mossambica in physiological Ringer solution. The responses were recorded as melanophore size index. It was observed that adrenaline, nor-adrenaline, phenylpropanolamine, clonidine and phenylepherine induced melanosome aggregation in a dose-dependent manner. Denervation of the fish melanophores increased the sensitivity of the melanophores to adrenaline but not to nor-adrenaline. Phentolamine (3.55 x 10(-5) M), prazosin (2.38 x 10(-5) M) and yohimbine (2.821 x 10(-5) M) significantly inhibited the aggregatory responses of the fish melanophores to adrenaline, nor-adrenaline, clonidine and phenylepherine. The blocking effect of yohimbine was significantly higher than that of prazosin. It is concluded that the effect of adrenaline is directly mediated through the receptors and alpha2 adrenoceptors are predominantly involved in the aggregatory responses of this fish melanophores, while alpha1 adrenoceptors presence has been indicated.     

Evaluation of biofilm of Aeromonas hydrophila for oral vaccination of Clarias batrachus--a carnivore model

Biofilm of Aeromonas hydrophila was evaluated for oral vaccination of walking catfish (Clarias batrachus L.). Fish were fed with fish paste incorporating biofilm (BF) or free cells (FC) of A. hydrophila for 20 days and monitored for serum antibody production up to 60 days post-vaccination. Serum agglutinating antibody titre and relative percent survival (RPS) following challenge were found to be significantly higher in catfish fed with BF vaccine compared to that with FC.     

Scaling of some metabolic enzymes in liver of a freshwater teleost: an adaptive mechanism

The activities of mitochondrial malate dehydrogenase (mMDH) and the total mitochondrial proteins increase as a function of body mass in the freshwater catfish, Clarias batrachus. It clearly indicates an increase in energy production in larger-sized individuals for various purposes including prey-predator interactions. The higher activity of lactate dehydrogenase (LDH) in larger fish may indicate more production of lactate for gluconeogenesis in the liver to meet emergency requirements of increased energy demand. However, the activity of cytoplasmic malate dehydrogenase (cMDH) decreases with the increasing body mass of the fish which reflects reduction in NADPH production and, in turn, reduced lipogenesis in liver of larger individuals. Thus, the present observations suggest an adaptive mechanism dealing with the higher energy budget, and reduced synthetic activities (lipogenesis) in the liver of larger-sized freshwater catfish. This type of biochemical scaling might be also supporting other metabolic pathways in order to adjust some physiological functions for survival in the aquatic environment.