Circadian Phase Dependent Thermal Stimulation of Ovarian Recrudescence in Indian Catfish,Clarias batrachus

Female Clarias batrachus acclimated to long photoperiod (13L:11D), were subjected to 30º ± 1ºC thermopulses of either 6-hour or 12-hour duration at different phases of the LD cycle during the late resting phase (first week of January) of their annual reproductive cycle. Six-hour pulses were given either at 0600 or 1200 or 1800 or 0000. Twelve-hour thermopulses were given at 0600 or 1800. The long photoperiods were started at 0530 and that of ambient at 0630 coinciding with the average timing of sunrise that prevailed during the period of the study. The results indicate that exposure to long photoperiod or constant high temperature induced gonadal growth (GSI) and elevated testosterone and oestradiol levels in plasma. The high temperature was significantly more effective in its action. Further, combination of long photoperiod and high temperature produced the strongest gonadal stimulation as gauged from GSI and the levels of steroid hormones. Interestingly, 30ºC thermopulses of 12-h duration when given at 0600 to fish held under long photoperiod induced gonadal development of comparable magnitude as observed in response to constant high temperature under long photoperiod. Thermopulses (30ºC) of 6-h duration given at 0600 or 1200 also induced significant gonadal recrudescence but of much lesser magnitude. Thermopulses either of 6-h or 12-h duration at 1800 failed to elicit any change in the variables under study. The results of cosinor analysis performed on the responses to 6-h thermopulses also substantiate that there is a rhythm in the sensitivity of C. batrachus to thermopulses. Thus it appears that in this species temperature-induced gonadal recrudescence would occur only following coincidence of high temperature with the thermoinducible phase. The underlying mechanism of this phenomenon might be circadian in nature.     

Effect of Pinealectomy on Re-entrainment of Air-gulping Activity in Indian Walking Catfish, Clarias batrachus

The present study was aimed to examine the effect of pinealectomy on re-entrainment of air-gulping activity in Indian walking catfish Clarias batrachus under various LD phases. Live Clarias batrachus of mixed sex (40-50g body weight) were procured from the local market and kept in the stock aquaria under the laboratory conditions for proper acclimation. Following 7 days of acclimation, animals were randomly selected from the stock aquaria and divided into 2 groups. The pineal was surgically removed from one group (P_xG) and the other group was treated as intact control group (IG). Both groups were exposed under LD 12:12 cycle inside the chronocubicles. In every 7 days LD schedule was delayed by 4 hours by lengthening of the light-on time. Both intact and pinealectomized animals are exhibited 24h rhythm in air-gulping behaviour and its entrainability irrespective of phase shifts of LD cycle. However, the phase angle of peak with reference to light on hour gradually decreased from phase 1 to phase 4, irrespective of treatment (intact/pinealectomized). Further, it has been noticed that the occurrence of multifrequency rhythm (24h, 12h and 6h) is being decreased from phase 1 to phase 4. It could be concluded that daily light-dark cycle plays an important role in modulating the rhythmic characteristics of air-breathing activity in Clarias batrachus and that pinealectomy does not modulate the effects of LD cycles on such activity.     

Circadian and Ultradian Variations in the Plasma Level of Maturational Gonadotropin (GTH II) in the Indian Catfish,Clarias batrachus

Analysis of changes in the plasma levels of GTH II over a 24-h day/night cycle revealed statistically significant circadian or ultradian variation or both in its circulating level during the gonadally active months of the reproductive cycle. The 24-h average and amplitude of circadian or ultradian rhythm in GTH II increased with the advancement of ovarian development and maturation. In April, a single peak in GTH II level was noticed in the night at 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradian rhythm) was noticed with two characteristic peaks, one in the photophase and the other in the scotophase. In addition, in May a statistically significant circadian rhythm in plasma GTH II was validated with a peak located at 20.1 h. These rhythms seem to have physiological significance. The ultradian rhythm with two peaks during the reproductively active phase appears to provide a suitable physiological milieu for the temporally different yet synchronous population of oocytes for the secretion of steroids. Thus, the observed temporal organization in GTH II may have physiological consequences leading to accomplishment of reproductive process at appropriate time of the year.     

Effect of Pinealectomy on Re-entrainment of Air-gulping Activity in Indian Walking Catfish,Clarias batrachus

The present study was aimed to examine the effect of pinealectomy on re-entrainment of air-gulping activity in Indian walking catfish Clarias batrachus under various LD phases. Live Clarias batrachus of mixed sex (40-50g body weight) were procured from the local market and kept in the stock aquaria under the laboratory conditions for proper acclimation. Following 7 days of acclimation, animals were randomly selected from the stock aquaria and divided into 2 groups. The pineal was surgically removed from one group (P_xG) and the other group was treated as intact control group (IG). Both groups were exposed under LD 12:12 cycle inside the chronocubicles. In every 7 days LD schedule was delayed by 4 hours by lengthening of the light-on time. Both intact and pinealectomized animals are exhibited 24h rhythm in air-gulping behaviour and its entrainability irrespective of phase shifts of LD cycle. However, the phase angle of peak with reference to light on hour gradually decreased from phase 1 to phase 4, irrespective of treatment (intact/pinealectomized). Further, it has been noticed that the occurrence of multifrequency rhythm (24h, 12h and 6h) is being decreased from phase 1 to phase 4. It could be concluded that daily light-dark cycle plays an important role in modulating the rhythmic characteristics of air-breathing activity in Clarias batrachus and that pinealectomy does not modulate the effects of LD cycles on such activity.     

Circadian and Ultradian Variations in the Plasma Level of Maturational Gonadotropin (GTH II) in the Indian Catfish, Clarias batrachus

Analysis of changes in the plasma levels of GTH II over a 24-h day/night cycle revealed statistically significant circadian or ultradian variation or both in its circulating level during the gonadally active months of the reproductive cycle. The 24-h average and amplitude of circadian or ultradian rhythm in GTH II increased with the advancement of ovarian development and maturation. In April, a single peak in GTH II level was noticed in the night at 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradian rhythm) was noticed with two characteristic peaks, one in the photophase and the other in the scotophase. In addition, in May a statistically significant circadian rhythm in plasma GTH II was validated with a peak located at 20.1 h. These rhythms seem to have physiological significance. The ultradian rhythm with two peaks during the reproductively active phase appears to provide a suitable physiological milieu for the temporally different yet synchronous population of oocytes for the secretion of steroids. Thus, the observed temporal organization in GTH II may have physiological consequences leading to accomplishment of reproductive process at appropriate time of the year.     

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.     

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.     

Effect of Pineal Extirpation on Daily and Long-Term Variations in Thermal Tolerance in a Tropical Catfish,Clarias batrachus

Thermal tolerance in laboratory acclimated Clarias batrachus was assessed by determining the critical thermal maximum (CTM) every 4 hours for 2 days in intact and pinealectomized (Px) animals during January and in sham-pinealectomized (sham-Px) and Px animals during April. In the intact and sham-Px group a statistically significant (P <0.005) diurnal cycle of thermal tolerance was validated which was asynchronous with that of the daily fluctuations in ambient temperature (Ta). A nocturnal elevation of thermal tolerance was observed in all the groups. Pineal removal resulted in a highly significant (P <0.001) increase of CTM. Additionally, pinealectomy abolished the normal diurnal cycle in CTM or dampened its amplitude considerably. In another experiment the long-term effect of pinealectomy on thermal tolerance was determined in sham-Px and Px fishes. CTM was significantly (P <0.05) elevated during the first three weeks following pinealectomy, pointing to a short-term control from the pineal on thermal tolerance. This study provides the first demonstration of a direct pineal influence on thermal tolerance and its temporal organization.     

Effect of Starvation on the Characteristics of 24-h Rhythm in Surfacing Activity of an Indian Freshwater Catfish, Clarias batrachus

The present study was aimed to examine the effect of starvation on the surfacing activity of an Indian freshwater catfish, Clarias batrachus. Live Clarias batrachus of mixed sex were purchased from the local market and kept in stock aquaria under natural daylength. After proper acclimation, animals were randomly selected and divided into two groups. Animals were exposed under natural daylength and kept in specially designed glass aquaria for recording of the surfacing activity. Animals of one group were fed once a day at a fixed time (14:00 h) while the other group had no food at all for a total period of experiment (8 days). Results clearly indicate that the surfacing activity exhibits a significant 24-h rhythm in both fed and starved groups of animals. Further, the acrophases of the activity are located during the dark phase. A statistically significant effect of time on surfacing activity was validated with the help of ANOVA. The night hour mean of the activity was found significantly higher as compared to the day hour mean. Results of ANOVA also revealed a statistically significant effect due to starvation. The activity in the fed group is significantly increased as compared with starved group. Further, statistically significant rhythms with τ = 12 h and 6 h have also been noticed in both fed and starved groups. It may be concluded that starvation does not affect the multifrequency rhythms in air-breathing activity of Clarias batrachus under natural daylength.     

Changes in the Pituitary-interrenal Axis after Gonadectomy in the Catfish,Clarias batrachus (Linn.)

The effects of gonadectomy on the cytological structure of the hypophysis and interrenal tissue of Clarias batrachus have been investigated. Forty days after gonadectomy remarkable hypertrophy of certain cyanophils, identified later as gonadotrops, has been observed followed by hyperplasia. The somatotrops also seem to undergo similar changes, and as a result the proximal pars distalis (PPD) increases enormously and encroaches upon the pars intermedia (PI). The gonadotrops undergo a gradual degranulation and become devoid of stainable cytoplasm by 90 days. No signet ring cells have been noticed at any stage. The cyanophils in the ventral region of the PPD, identified as thyrotrops, also show degranulation, but to a comparatively limited degree. The ACTH cells undergo gradual hypertrophy and degranulation. A progressive increase is noticed in the nuclear diameter. The interrenal cells are activated as indicated by the enhanced nuclear indices. It is suggested that a fall in gonadal steroids may result in ACTH release which in turn activates the interrenal cells.     

On the Food of the Air-breathing Catfish,Clarias batrachus (LINN.) Occurring in Wild Waters

The paper describes the food of Clarias batrachus (LINN.) occuring in derelict and swampy waters of the Bihar region of the Indian subcontinent. The study revealed that the early post-larval stage is exclusively planktophagous while in the late post-larval stage it starts including larger organisms in its diet. Juvenile stage is predominantly insectivorous. Though adults have a wide range of food preference, the insect material forms by far the most important source of their food. The fish did not appear to possess enough sense to sort out edible from non-edible forms. March and September are the peak periods of relatively intensive feeding. The intensity of feeding in relation to the size of the fish showed that the average weight of food/g weight of the fish decreases with increasing weight of the fish.     

Genetic Structure of Different Populations of Walking Catfish (Clarias batrachus L.) in Bangladesh

Information on genetic variation is essential for conservation and stock improvement programs. Seven dinucleotide microsatellite loci were analyzed to reveal genetic variability in three wild populations (Kella beel, Hakaluki haor, and Shobornokhali beel) and one hatchery population of the freshwater walking catfish, Clarias batrachus, in Bangladesh. Upon PCR amplification, the alleles were separated on polyacrylamide gel using a sequencing gel electrophoresis system and visualized by the silver-staining method. The loci were polymorphic (P95) in all the populations. Differences were observed in number and frequency of alleles as well as heterozygosity in the studied populations. Current gene diversity (He) was higher than expected under mutation-drift equilibrium, significantly in the Hakaluki haor and Shobornokhali beel populations, indicating a recent genetic bottleneck. Population differentiation (FST) values were significant (P<0.05) in all the population pairs. A relatively high level of gene flow and a low level of FST values were found between wild population pairs compared to hatchery-wild pairs. The unweighted pair group method with averages dendrogram based on genetic distance resulted in two major clusters: the hatchery population was alone in one cluster whereas the three wild populations made another cluster. The results reflect some degree of genetic variability in C. batrachus populations indicating potentialities for improving this species through a selective breeding program. The results revealed a recent bottleneck in some wild populations of C. batrachus. Protection of habitat may help increase the population size and lower the risk of vulnerability of the species in the future.     

Circadian variations in circulating plasma sex steroids in female catfish, Clarias batrachus (Linn.).

Estradiol (E2) and 17 alpha-hydroxyprogesterone (17 alpha-OHP) levels exhibited significant circadian rhythms in the prespawning phase of the reproductive cycle. Pattern of rhythm was unimodal. Whereas, in the spawning phase E2 levels did not show significant fluctuations in their daily cycle whereas 17 alpha-OHP levels showed significant rhythm (P less than 0.001). Amplitude of rhythm of E2 was greater in prespawning phase while 17 alpha-OHP showed greater amplitude in spawning phase.     

Retinal Pigment Epithelium–Calycal Processes Association in the Catfish Clarias batrachus(Linnaeus, 1758)

Abstract In the duplex retina of the catfish Clarias batrachus(Linnaeus, 1758), the apical processes of the pigment epithelial cells have been found by transmission electron microscopy to be in intimate contact with the calycal processes around the basal portion of the photoreceptor outer segments. It is hypothesized that the retinal pigment epithelium effectively transports synthesized products and metabolites to the photoreceptor inner segments via the anatomical zone of the apical–calycal processes interface in this species.     

Circadian Phase Dependent Pharmacokinetics of Disopyramide in Mice

The focus of the reported work is investigation of disopyramide chronopharmacokinetics in the mouse. Different groups of male NMRI mice maintained under controlled environmental conditions (LD: 0600-1800) received a single intraperitoneal injection of disopyramide (30mg per kg of body weight) at one of four different fixed time points of a 24-h period, i.e. 1000, 1600, 2200 or 0400. Blood samples were taken 0.5,1,2,3,4 and 6 hr after drug administration and total and free plasma levels of disopyramide were measured by an immunoenzymatic method.

Our data showed statistically significant circadian rhythms in the following pharmacokinetic parameters: highest volume of distribution = 3.91 ± 0.211kg^-1 at 2200 (circadian amplitude, half the peak-to-trough difference relative to the 24-hr mean multiplied by 100, is 34%); highest area under concentration curves = 16.06 ± 1.03μgml^-1hr^-1 at 0400 (circadian amplitude = 43%) and highest clearance = 3.04 ± 0.191hr“kg”¹ at 2200 (circadian amplitude = 21%). Protein binding of the drug was shown to ^he circadian time dependent. Alpha and beta phase elimination half-lives were not found to be significantly circadian phase-dependent. Thus circadian changes in disopyramide clearance may represent circadian changes in the drug's volume of distribution.     

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 .     

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.     

EST-based identification of immune-relevant genes from spleen of Indian catfish, Clarias batrachus (Linnaeus, 1758)

A normalized cDNA library from spleen of Indian catfish, Clarias batrachus, was constructed with a redundancy factor of 2.29. A total of 2045 clones from the library were single-pass sequenced, which generated 1937 high quality ESTs with an average read length of approximately 700 bp. Based on sequence similarities, 65 ESTs were found to be associated with immune functions, which were mainly associated with response to stress, response to chemical stimulus, cellular response to stimulus, response to external stimulus, immune response and regulation of response to stimulus. The immune-relevant gene for CD141, thrombomodulin, has been identified in Teleosts for the first time. Six EST-SSRs and three SNPs were found associated with eight immune-relevant genes. These markers associated with important immune genes would be useful for the identification of trait associated alleles for marker-assisted selection. The identification of the putative immune-related genes provides a meaningful framework to understand the Indian catfish immune system and defense mechanisms.     

Circadian Variation in Circulating Levels of Melatonin, Testosterone and Estradiol-17β in a Tropical Freshwater Catfish, Clarias batrachus, during Different Phases of the Annual Reproductive Cycle

In the present investigation, daily variations in plasma levels of melatonin, testosterone and estradiol-17β were analysed in the tropical freshwater catfish, Clarias batrachus during early and late-preparatory, pre-spawning, late-spawning and post-spawning phases of its annual reproductive cycle. Plasma melatonin levels exhibited a significant circadian rhythm during all the reproductive phases but peaks were invariably at night. The amplitude of melatonin was high during the early-preparatory phase and low in the pre-spawning phase. Testosterone also displayed significant rhythm during all the studied phases except post spawning phase. Estradiol-17β revealed diurnal rhythm only during preparatory and pre-spawning phases. The peak in the levels of plasma testosterone and estradiol-17β were recorded during the photophase. During the late-preparatory phase, the rhythm of testosterone coincided with the rhythm of estradiol-17β.     

Physiological responses to acute experimental hypoxia in the air-breathing Indian catfish, Clarias batrachus (Linnaeus, 1758)

With an aim to study the mechanism of adaptation to acute hypoxic periods by hypoxia-tolerant catfish, Clarias batrachus, the mass-specific metabolic rate (VO₂) along with its hematological parameters, metabolic response and antioxidant enzyme activities were studied. During progressive hypoxia, C. batrachus was found to be an oxyconformer and showed a steady decline in its aquatic oxygen consumption rate. When C. batrachus was exposed for different periods at experimental hypoxia level (0.98?±?0.1 mg/L, DO), hemoglobin and hematocrit concentrations were increased, along with decrease in mean cellular hemoglobin concentration, which reflected a physiological adaptation to enhance oxygen transport capacity. Significant increase in serum glucose and lactate concentration as well as lactate dehydrogenase activity was observed. Antioxidant enzymes were found to operate independently of one another, while total glutathione concentration was unaffected in any of the tissues across treatments. These observations suggested that hypoxia resulted in the development of oxidative stress and C. batrachus was able to respond through increase in the oxygen carrying capacity, metabolic depression and efficient antioxidant defense system to survive periods of acute hypoxia.