2,4,6-Trichlorophenol (2,4,6-TCP) is a common waste among the resulting chlorophenols generated in the production of common products classified as an extremely toxic, mutagenic, carcinogenic and highly persistent xenobiotic in the environment. To evaluate the impact of 2,4,6-TCP in aquatic systems, the catfish species Clarias batrachus has been selected to test its toxicity due to its high market value and consumption in India. Here is presented the impact of this compound on different physiological parameters of fish: haematological parameters (haemoglobin, total erythrocyte count, total leucocyte count and mean corpuscular haemoglobin), biochemical parameters (total serum protein and total serum glucose), growth and reproductive parameters (condition factor, hepatosomatic index, maturity index, specific growth rate, growth hormone, 17β-estradiol and testosterone), exposed to two concentrations of 2,4,6-TCP (0.5 mg/L and 1 mg/L — 1/10th and 1/20th of the LC₅₀) for a period of 15, 30 and 45 days. The results showed that C. batrachus even when exposed to the lower concentration (0.5 mg/L) for the shortest time (15 days) negatively impacted the organism in all the assessed parameters. This was highlighted by the Integrated Biomarker Response index (IBR), showing worse scores for the treatments (up to 20 × worse than the control). This work highlights the importance of continued research on the impact of 2,4,6-TCP, on an important commercial, supported by the high environmental persistence of this compound that can reach the same range of tested concentrations.

The present field study evaluates the health status of the catfish Clarias batrachus reared in coal mine effluent (CME)-fed pond water at Rajrappa mining complex using biochemical, haematological and histopathological parameters. Simultaneously, risk assessment along with recovery response of the CME intoxicated fish following their treatment with CME-free freshwater was also studied. The CME-fed pond water fish revealed significant decrease in biomolecules concentrations and considerable increase in activities of several enzymes along with metallothionein level as compared to control. The impaired regulation of metabolic function was also revealed by blood parameters showing significant decrease in haemoglobin content (8.78 ± 0.344 g/100 mL) and red blood cells count (1.77 ± 0.12 × 10⁶ mm³) while substantial elevation in white blood cells (187.13 ± 9.78 × 10³ mm³). The histopathological study also confirmed the changes including hypertrophy of club cells of skin, swelling of secondary lamella of gills, extensive fibrosis in liver and glomerular shrinkage with increased Bowman’s space in kidney. Potential health risk assessments based on estimated daily intake and target hazard quotient indicated health risks associated with the consumption of such fishes. The CME-contaminated fish when transferred to CME-free freshwater exhibited decreased metal content accompanied by eventual recovery response as evident by retrieval in biochemical and haematological parameters. Withdrawal study also revealed restoration in the activity of different marker enzymes in fish tissues including blood as well as recovery in their cellular architecture. The results of the present study validate the depuration process as an effective practice for detoxification of fish contaminated with effluent.

In the present study, an attempt has been made to analyze the toxicity of fluoride and arsenic on morphology and behaviour of fish Clarias batrachus. Based on 96 hour LC50 values at the 95% confidence limits of sodium fluoride (NaF) and arsenic trioxide (As2O3) obtained from the preliminary tests, various sub-lethal concentrations of NaF and As2O3 were selected for combined toxicity testing. During the experiment, fish were regularly observed for any changes in their external morphology and behaviour. Behavioural changes were observed in terms of air gulping, opercular movement, swimming activity, body position, general activity and food sensitivity. Control fish remained normal throughout the experiment period (96 hour) but erratic, exodus and speedy movements were found in all treated groups. The number of air gulps (per 15 min, 24-96 hour) significantly increased (P<0.001) in the exposed Group I (20 mg.L-1 As2O3) as compared to control. A significant increase (P<0.01) in the number of opercular movements (per min for 24-96 hour) was recorded in treatment groups as compared to control. Apparent changes such as excessive mucous secretion, increased body discolouration, loosening of skin and complete loss of skin (head region and fins) were also observed. Skin loss was more intense in fish subjected to Group I.

Heavy metal poisoning means an excess of the required concentration that is found naturally on earth. In the present experiment, it has been observed that the natural water source surrounded by mountains is also polluted with arsenic because these heavy metals like arsenic are naturally contained in rocks that accumulate in the water source with soil erosion and rain. In this experiment arsenic was found in the water of Chhilpura pond, in which the haematology and biochemistry of catfish (Clarias batrachus) were studied, it was found that the RBC, haemoglobin, PCV, MCV, MCH, platelets, glucose and protein contents of catfish were found to be relatively low as compared to the control, whereas the WBC was observed to be higher to control and differential leucocyte count fluctuations were observed. It can be inferred from this experiment that heavy metals such as arsenic alter the haematology and biochemistry of catfish (Clarias batrachus).