ABSTRACT
Aim: The present study was conducted to determine the tolerance to reduced oxygen level (hypoxia) and the behavioural and biochemical responses of mrigal, Cirrhinus mrigala to environmental hypoxia. Methodology: Cirrhinus mrigala were subjected to LC50 test for 96 hr and the mortality were recorded. In a second experiment, the fishes were subjected to a stressful, but safe limit of hypoxia (0.5±0.04 mg l-1) and the behavioral responses and serum metabolites (glucose, lactate, total lipids, free amino acids and ammonia) were evaluated for 96 hrs. Results: A median lethal concentration (LC50, 96 hr) value of 0.25 mg l-1dissolved oxygen) was estimated for mrigal. The upper safe limit was 0.49 mg l-1 DO and the lower lethal limit was 0.19 mg l-1 DO. Gill ventilation frequency increased under severe hypoxic conditions and decreased with exposure time. The serum level of glucose, lactate and total lipids increased significantly (P<0.05) within 24 hr of exposure to hypoxic conditions. Free amino acids and ammonia contents were not altered by a four day exposure to hypoxia. Interpretation: The present study explains the basic metabolic and behavioural mechanism behind the hypoxia tolerance of Indian Major Carp, mrigal assisted by alterations in gill ventilation and metabolic responses.
ABSTRACT
Experiments were conducted to evaluate the toxic effects of monocrotophos in ciliate models Paramecium caudatum and Oxytricha fallax. In acute toxicity studies higher concentrations of monocrotophos caused marked increase in mobility of cells exhibiting rocking movements within two mins of exposure but were decreased after 30 mins. LC50 value by mortality curve for 3 hr acute toxicity test of Oxytricha fallax and Paramecium caudatum was found 307.744±33.27mg l-1 and 332.284±57.52 mg l-1 respectively. Oxytricha fallax was found sensitive than Paramecium caudatum to monocrotophos. In acute exposure cells showed deformities such as swelling, oval shaped deformity and in higher concentrations shortening of longitudinal axis with blackening of cytoplasm occurred. The length of paramecia was reduced prominently. Similarly, enlargement of contractile vacuole and stress egestion of food vacuoles was also observed. The morphological studies showed the changes in shape, size, colour and width of Paramecia and Oxytricha. Frequencies of macronuclear aberrations were significant showing deformities such as rod shaped, elongation, fragmentation, diffusion and total absence of nucleus and were concentration dependent. The data provided in the present study, on interaction of pesticides with nuclear structure can be of immense value because most of these pesticides have been reported to have carcinogenic, mutagenic and teratogenic properties.