T.P. Singh

Changes in tissue lipid levels in the freshwater catfishClarias batrachus associated with the reproductive cycle

The levels of free fatty acid (FFA), monoglyceride (MG), diglyceride (DG), triglyceride (TG), phospholipid (PL), free cholesterol (CF) and esterified cholesterol (CE) were measured in the liver, plasma, ovary, abdominal fat and muscle during different phases of the annual reproductive cycle in femaleClarias batrachus. During the preparatory phase, hepatic lipogenic activity predominated over mobilization and consumption. In the prespawning season, an increased hepatic lipogenic activity was maintained, but lipids were transferred from the liver to the ovary. In the spawning phase, the diminished food intake, and enhanced caloric demand for spawning behaviour and activity limited hepatic lipogenic activity, and TG lypolysis was increased as was the production of more FFA. Maximum accumulation of vitellogenin, as reflected by maximum rise in ovarian PL titre was characteristic of this phase. Marked reductions in ovarian lipid occurred during the postspawning phase. In the resting phase, there was a recovery of lipogenic activity, but PL synthesis was still inhibited. In contrast to other investigated teleosts, there were extremely high level of FFA in liver, plasma, ovary and muscle throughout the annual reproductive cycle inC. batrachus. FFA appears to be the main lipid metabolite which had a very high turnover. As evidenced by the high TG content, abdominal fat seems to be the main fat depot, not the liver and muscle.

Effect of endosulfan (thiodan) on vitellogenesis and its modulation by different hormones in the vitellogenic catfish Clarias batrachus

This programme was planned in order to study the reproductive dysfunction caused by endosulfan in the fish Clarias batrachus with special reference to vitellogenesis. Vitellogenin was measured by radioimmunoassay. Endosulfan caused a drastic reduction in the plasma vitellogenin which was partially reversed by estradiol-17 beta (E2) in intact and ovariectomized fish. Hormones in combination were more effective than any single hormone in overcoming the impact of endosulfan. Triiodothyronine (T3), ovine luteinizing hormone releasing hormone (oLHRH) were effective in minimizing the effect of endosulfan whereas cortisol (F) and ovine somatotropic hormone (oStH) did not reduce the effect of endosulfan. Amongst the combined hormone treatments, E2 + oLHRH and E2 + T3 were the most potent in overcoming the effect of endosulfan on vitellogenesis.

Pesticides induced changes in circulating thyroid hormones in the freshwater catfish Clarias batrachus

1. Effects of endosulfan, malathion and carbaryl on circulating T4, T3 and T3/T4 ratio in the freshwater catfish, C. batrachus have been studied during reproductively active phases, i.e. vitellogenic and post-vitellogenic phases of its annual reproductive cycle. 2. Endosulfan provoked a significant increase in T4 and a decrease in T3 as well as the T3/T4 ratio. 3. Malathion decreased T3 and T3/T4 ratio without altering the level of T4 in circulation. 4. Carbaryl caused a decline in the level of T4 and an elevation in T3 and T3/T4 ratio.

Effect of endosulfan on thyroid physiology in the freshwater catfish, Clarias batrachus

Effects of endosulfan on thyroid physiology have been studied in the female freshwater catfish. Clarias batrachus during the pre-spawning and spawning phases of its annual reproductive cycle. Effects of endosulfan varied with the length (96 h and 16 days) of exposure, reproductive status of the fish and organ. The 96-h endosulfan exposure significantly increased the level of thyroxine (T4) in serum and pharyngeal thyroid follicles concurrent with induction of peroxidase activity. However, triiodothyronine (T3) level and T3/T4 ratio decreased in serum and pharyngeal thyroid gland. No change was noticed in any of these parameters in the anterior kidney but in the posterior kidney endosulfan reduced T3 and T3/T4 ratio without affecting T4 levels and peroxidase activity. Sixteen days of endosulfan treatment also had a similar impact, except that it did not influence the studied parameters in pharyngeal thyroid.

Carbaryl-induced thyroid dysfunction in the freshwater catfish Clarias batrachus

Freshwater female catfish, Clarias batrachus, were exposed to sublethal concentrations of carbaryl (12 mg/liter for 96 hr and 5 mg/liter for 16 days) during the prespawning and spawning phases of their annual reproductive cycle. The effects on the levels of thyroxine (T4) and triiodothyronine (T3), the T3/T4 ratio, and the extrathyroidal conversion of T4 to T3 were studied in serum, pharyngeal thyroid, and anterior and posterior kidney. Carbaryl exposure for 96 hr suppressed T4 but elevated T3 and the T3/T4 ratio in serum during both phases of experimentation. However, 16 days exposure caused a decline in T4 as well as in T3 and in the T3/T4 ratio. In the pharyngeal thyroid, carbaryl increased T4 as well as peroxidase activity and decreased T3 and the T3/T4 ratio. Its treatment for 96 hr did not elicit any change in the parameters studied in the anterior kidney, whereas in the posterior kidney it suppressed the levels of T4 and T3, peroxidase activity, and the T3/T4 ratio. However, carbaryl exposure for 16 days provoked increases in T4 and peroxidase activity but decreases in T3 and the T3/T4 ratio in anterior kidney. In posterior kidney, it did not change T4 and peroxidase activity, but decreased T3 and the T3/T4 ratio. It also stimulated extrathyroidal conversion of T4 to T3.

The effect of malathion and γ-BHC on the lipid metabolism in relation to reproduction in the tropical teleost, Clarias batrachus

In the present study, female Clarias batrachus were exposed to two sublethal concentrations of gamma-BHC (2 and 8 microg litre(-1)) and malathion (1 and 4 microl litre(-1)) for 4 weeks during different phases of their reproductive cycle. Impact of these pesticides on free fatty acids, monoglycerides, diglycerides, triglycerides, phospholipids, free and esterified cholesterol in the liver, plasma, ovary and muscle was assessed. During the pre-vitellogenic and regressed phases, they suppressed the levels of fatty acids and glycerides in the liver, but had no effect on their levels in the plasma, ovary and muscle. However, in the vitellogenic phase, fatty acids in the liver and plasma were increased, but were decreased in the ovary and muscle. Glycerides were also decreased in the studied tissues. In the post-vitellogenic phase, these pesticides increased the levels of fatty acids and glycerides in the liver and ovary, but decreased their levels in the plasma. Both pesticides decreased hepatic phospholipids in the pre-vitellogenic phase, while in the vitellogenic phase only gamma-BHC reduced its levels in the liver. These pesticides also restricted their mobilisation to the ovary. Cholesterol biosynthesis seemed unaffected, but the hydrolysis of esterified cholesterol to free cholesterol was adversely affected during the period of estrogen biosynthesis.

Impact of pesticides on lipid metabolism in the freshwater catfish, Clarias batrachus, during the vitellogenic phase of its annual reproductive cycle

Specimens of either sex of the freshwater catfish Clarias batrachus were exposed to safe and sublethal concentrations of an organochlorine, gamma-BHC (2 and 8 ppm), and an organophosphorus compound, malathion (1 and 4 ppm), for 4 weeks during the vitellogenic phase of their annual reproductive cycle. The effects on total lipid and its various fractions, viz., free fatty-acids, monoglycerides, diglycerides, triglycerides, phospholipids, free cholesterol, and esterified cholesterol, were studied in the liver, plasma, gonads, and muscle. Except for elevated liver lipid in the male in response to malathion, no significant change in total lipid could be observed following pesticide exposure. However, various lipid fractions responded differently to two concentrations of the pesticides. Both pesticides affected the metabolism of nonpolar and less polar lipids alike. Malathion inhibited only mobilization of hepatic phospholipid to gonads but not its hepatic biosynthesis, whereas gamma-BHC reduced its synthesis in the liver as well. These pesticides seemed to restrict the conversion of esterified cholesterol into free cholesterol without affecting the biosynthesis of cholesterol as such. In both sexes, esterification of free fatty acids to acyl glycerides and their mobilization from liver to gonads seemed to be restricted as a result of pesticides action.

Thyroid physiology impairment by malathion in the freshwater catfish Clarias batrachus

Effects of malathion on serum and glandular thyroxine (T4), triiodothyronine (T3), the T3/T4 ratio, peroxidase activity, and extrathyroidal conversion of T4 to T3 have been studied in the freshwater catfish Clarias batrachus during the prespawning and spawning phases of its annual reproductive cycle. Malathion inhibited T4 secretion in the kidney, but accelerated T4 synthesis in the pharyngeal thyroid. This pesticide also inhibited the extrathyroidal conversion of T4 to T3 in serum during both the studied phases.

Pesticide-induced changes in peripheral thyroid hormone levels during different reproductive phases in Heteropneustes fossilis

Effects of gamma-BHC (an organochlorine) and malathion (an organophosphorus) exposure on plasma triiodothyronine (T3) and thyroxine (T4) levels have been studied in the freshwater catfish, Heteropneustes fossilis, during its annual reproductive cycle. After 4 weeks exposure of gamma-BHC (8 and 16 ppm) and malathion (10 and 20 ppm), the effects on plasma T3, T4, and T3/T4 ratio varied during different reproductive phases. Malathion seems to have a stimulatory effect, while gamma-BHC seems to have an inhibitory effect on extrathyroidal conversion of T4 to T3. Changes in levels of various thyroid hormones during different reproductive phases occurred most probably due either to inhibited (in response to gamma-BHC) or to stimulated (in response to malathion) extrathyroidal T4 monodeiodination and their altered excretion or consumption rate.

Seasonal effects on the diel changes in circulating thyroid hormones in the freshwater catfish Clarias batrachus

Abstract The profiles of thyroxine (T4) and triiodothyronine (T3) in serum were monitored at 4 h intervals over a 24 h cycle in nine months of the year in females of the freshwater catfish. Clarias batrachus by means of radioimmunoassay. The results exhibited significant seasonal changes of the daily cycles in the titres of T4 and T3. Interestingly, unlike earlier reports, T4 and T3 showed two peaks in the serum; one in the photophase and the other in the scotophase of the 24 h cycle in all of the studied months. There were significant variations in their peak timings and magnitudes over the year.