Impact of fishing methods on conservation of ichthyofauna of river Relli in Darjeeling Himalaya of West Bengal.

Impact of fishing methods and gears used on fish faunal diversity in spring–fed torrential river Relli in Darjeeling hill area of West Bengal was investigated in the present study. The fish species available in the river provide nutrition and recreation (rarely income generating) for a large number of people residing along the river bank and nearby villages and towns. The fishing methods observed therein have been categorized as, i) Scientific fishing methods, that is, collection of required number and size of fish so that sufficient population of fish remains balanced in the nature. ii) Unscientific fishing methods, that is, indiscriminate killing of large number of fish which adversely affect the water quality of rivers. Ten types of fishing methods are practiced in this area, for example, diversion of river channel, cast netting, scoop netting, angling, fish spearing, rock striking or hammering, dynamiting, electric fishing, river poisoning and traps utilized. Over the years uncontrolled and often indiscriminate fishing in the unmanaged hill-stream has resulted in a sharp decline in fish resources. The study gives a clear picture on the anthropogenic pressure on the river Relli and provides baseline data which may be helpful for conservation and management of the fish species and also formulating new fishery policy.

Toxicity of neem pesticides on a fresh water loach, Lepidocephalichthys guntea (Hamilton Buchanan) of Darjeeling district in West Bengal.

Static renewal bioassay tests were conducted to evaluate the acute toxicity of two neem based biopesticides, applied widely on tea plantation namely, Nimbecidine and Neem Gold either separately as well as, in combination to the fingerlings (mean body length- 4.46 +/- 0.15 cm; mean body weight- 0.49 +/- 0.15g) of a fresh water loach, Lepidocephalichthys guntea (Hamilton Buchanan) acclimatized to laboratory conditions prior to experiment. The 96 hours LC50 values for Nimbecidine and Neem Gold and the combination of the two were 0.0135 mgl(-1), 0.0525mgl(-1) and 0.0396 mgl(-1), respectively. The regular water quality analysis showed, that with increasing doses of biopesticides, dissolved oxygen level was lower and other parameters like pH, free carbon dioxide, total alkalinity total hardness, chloride ions of water increased. The fish under toxicity stress suffered several abnormalities such as erratic and rapid movement, body imbalance and surface floating responding proportionately to the increase in concentrations of the toxicant biopesticides. The 96 hours LC50 values proved Nimbecidine more toxic than Neem Gold and the combination of the two biopesticides.

Influence of the organophosphorus insecticide phosphamidon on lentic water.

The inland freshwater resources are being increasingly subjected to heavy stress as a result of indiscriminate dumping of industrial wastes, domestic sewage and agricultural run-off causing deterioration of the water quality and adverse impact on aquatic biota. Pesticides drained to the aquatic environment are primarily of agricultural origin. Phosphamidon (widely used organophosphate pesticide in paddy field) significantly reduced dissolved oxygen (DO) at 1.8 mg/l exposure and reduced alkalinity at 0.9 and 1.8 mg/l. Hardness also reduced gradually but not significantly. Free carbondioxide was increased significantly at 1.8 mg/l of the insecticide compared to control. The insecticide had no influence on pH and temperature. There was maximum reduction of phytoplankton and zooplankton population at 1.8 mg/l of phosphamidon. Though gradual reduction of plankton community was also noticed at different lower concentrations of pesticides but in case of phytoplankton an abrupt reduction (about 50% of the control) was observed. The normal behaviour and feeding rate of air breathing teleost, Channa punctatus was also hampered. Therefore, phosphamidon even at low concentrations may create disorders in the aquatic ecosystem.

Hydrobiological study of lake Mirik in Darjeeling Himalayas.

Some hydrobiological features of lake Mirik, situated in the Darjeeling Himalayas were studied during May to October, 2000. Water temperature showed abrupt fluctuations. The pH was generally acidic. Dissolved oxygen increased steadily with increasing rainfall and recorded highest in late August (12.6 mgl(-1)). The gross primary productivity had a highest value of 87.50 mg C m(-3) hr(-1). Chlorophyceae and Cyanophyceae were identified among phytoplanktons. Zooplanktons were represented by Cladocerans and Copepods. The study revealed higher concentration of nutrients at certain pockets of the lake, which points to increasing human influences in the system, and, the water cannot serve as a scarcity alternative for drinking purpose.