Endosulfan-mediated Biochemical Changes in the Freshwater Fish Clarias batrachus

Objective Endosulfan is an extremely toxic organochlorine pesticide to aquatic organisms which might be hampering fish health through impairment of metabolism sometimes leading to death. So an experimental protocol was designed to look at endosulfan effects on a number of selected biochemical endpoints as well as to develop a mechanistic understanding of biochemical effects of endosulfan in freshwater fish. Methods The adult freshwater catfish Clarias batrachus were collected and acclimatized to laboratory condition for two weeks prior to experimentation. The toxicity bioassay test of commercial grade endosulfan (35% EC) was conducted for 21 days to determine its initial lethal concentration. The fish were exposed to sublethal concentration of endosulfan (0.06 mg/L) for 21 days. Pesticide - withdrawal experiments were also performed to study recovery. Protein synthesis inhibitors were injected to know the possible mechanism of recovery. The specimens of C. batrachus were sacrificed and brain, liver and caudal white skeletal muscle were removed. Tissues were homogenized and fractions were obtained by differential centrifugation. The activities of citrate synthase (CS), glucose 6-phosphate dehydrogenase (G6-PDH) and lactate dehydrogease (LDH) were assayed spectrophotometrically. Similarly, DNA, RNA and protein content were measured as per standard procedure. Results The exposure of sublethal concentration of endosulfan decreased the activity of citrate synthase (CS) and glucose 6-phosphate dehydrogenase (G6-PDH) in the brain, liver and skeletal muscle of the freshwater catfish, C. batrachus. The brain lactate dehydrogenase (LDH) activity was also reduced in response to endosulfan toxicity. The maximum reduction in activities of these enzyme was 34%-43%. Withdrawal of endosulfan restored the enzyme activity to control level in all the three tissues. The recovery in enzyme activity appears to be due to dissociation of endosulfan or its metabolite(s) from the enzyme molecules and/or fresh synthesis of enzymes. The treatment of actinomycin D or cycloheximide partially inhibited the withdrawal-dependent increase in enzyme activity. This substantiates de novo synthesis of enzyme during recovery period. Since the reduction in enzyme activity was more pronounced in response to actinomycin D, endosulfan might be inhibiting the transcription process. But endosulfan did not produce any significant effect on DNA content and RNA/DNA. However, the RNA and protein contents of brain, liver and skeletal muscle decreased significantly in tissues. The maximum decrease in RNA and protein was approximately 30%-37%. Withdrawal of endosulfan from the medium for 21 days restored the RNA, and protein contents nearly to their control levels. The treatment of actinomycin D or cycloheximide partially inhibited the withdrawal- dependent increase in these macromolecular contents. This effect was more pronounced in case of actinomycin D which again supports the possibility of endosulfan-induced inhibition at transcription level. Conclusion The present study suggests endosulfan-induced impairment of metabolism in fish, which appeared to be due to inhibition of transcription at some unknown points.

Enzymatic and Ultrastructural Studies in a Freshwater Catfish: Impact of Methyl Parathion

Exposure to a sublethal concentration of methyl parathion (MEP) reduced the activity of cytoplasmic malate dehydrogenase. mitochondrial malate dehydrogenase, and lactate dehydrogenase by 30 to 49% in the liver and the skeletal muscle of the freshwater catfish, Clarias batraclms, after 7 days. The activities then began to recover and reached the control levels on the 28th day of MEP exposure. A complete recovery occurred on the 7th day when MEP was withdrawn from the medium after an exposure for 1 week. The withdrawal-dependent recovery in the activities was inhibited partially or completely by actinomycin Dandcycloheximide, suggesting de nova synthesis of the enzymes during the recovery period. A conjoint treatment of MEP and triiodolhyronine (T_3) restored the activities to control levels, indicating T_3 protection against the pesticide toxicity. SDS-PAGE of the cytoplasmic fraction of the liver showed some noticeable changes in the protein pattern after an exposure to MEP. Ultrastructural studies on MEP-treated liver cells showed disappearance of the glycogen granules and appearance of numerous smooth endoplasmic reticulum, lysosomal dense bodies, and swollen mitochondria. These changes in the liver are an indication of hepatic toxicity leading toward necrosis.(c) 1990 Academic Press.Inc.

A Review on Molecular Physiology of Malate and Lactate Dehydrogenases in Fishes

The malate(EC 1.1.1.37)and lactate(EC 1.1.1.27)dehydrogenases are themetabolic enzymes directly or indirectly involved in energy production,gluconeogenesis and lipogenesis.Malate dehydrogenase(MDH)exists in twoisoenzymic forms,cytoplasmic(cMDH)and mitochondrial(mMDH),composed of Aand/or B subunits(dimeric molecule:MW 40,000-120,000).Lactate dehydrogenase(LDH)has tetrameric(MW 35,000-110,000)structure made up of either A and/or B,orC(C,E,F)subunits.They catalyze an ordered bisubstrate(substrate and coenzyme)

Study of Bio-fertilizer Produced from Agro-waste (Sesame Straw) and Cow Dung Using Eisenia fetida and Perionyx sansibaricus in Arid Environment

In this study,an analysis of organic fertilizer of an agro-waste(Sesame straw)plus cow dung was carried out using an epigeic earthworm species Eisenia fetida and Perionyx sansibaricus.Sesame straw is abundantly produced after each harvesting of the crop in Kharif season in arid region of tropical India.The compost produced in presence and absence of earthworm exhibit significant(P<0.001)and non-significant(P>0.05)changes in physicochemical properties respectively.In control bedding,the values of water holding capacity enhanced significantly(P<0.05)by 1.28 fold,while organic carbon and C/N ratio decreased significantly(P<0.05)by 19.93%and 31.25%respectively after 60 days of composting.Working of E.fetida in the bedding material showed significant(P<0.001)difference in the level of pH,electrical conductivity,water holding capacity,organic carbon,total nitrogen,C/N ratio,available phosphorous and available potassium.After 60 days of working of P.sansibaricus,these physicochemical properties of the bedding substrate also changed significantly(P<0.001).Analysis of vermibed showed a gradual increase in electrical conductivity,water holding capacity,total nitrogen,available phosphorus and available potassium by 1.51,1.86,1.95,1.78 and 1.75 fold respectively.While the values of pH,organic carbon and C/N ratio declined by 9.30%,41.80%and 71.48%respectively within 60 days of decomposition.Thus,E.fetida and P.sansibaricus can be applied for production of organic fertilizer of sesame chaff plus cow dung to fulfill the requirement of bio-fertilizers for organic farming and agro-waste management in arid environment.