Inland Fisheries

8.2.2.4 Stupefying Gears

Certain devices are made use of in stupefying the fish either mechanically, chemically or electrically to ease their capture. These methods are prohibited in responsible fisheries.

1. Mechanical stupefying is done by throwing stones at the fish, beating with clubs or mallets and by using explosives like dynamite (Dynamite Fishing). However, the use of explosives is environmentally harmful for the entire fish population and also the fishing grounds.
2. Fish poisoning - Chemicals like copper and lime are used to poison the fish. Plant poisons extracted from ichthyotoxic plants containing saponin are used to poison and stupefy the fish. Traditionally some tribals used to kill or narcotize fishes using latex or powdered parts of some plants. Some plant poisons are used in aquaculture programme to eradicate undesirable (weed) fishes from the nurseries or fish farms. Derri’s root powder (Roots of Derris trifoliata) containing an ingredient called ‘Rotenone’ is the most commonly used fish poison, acting like a contact poison which damages the respiratory system and ultimately causes death. The poison is effective in shallow waters up to 1.5 m depth on hot sunny days with water temperature above 25º C. Powdered seed kernel of Croton tiglium, powdered root of Millettia sp., seed powder of Barringtonia sp., unripe fruit powder of Randia sp., bark powder of Walsura picidia are indigenous plant poisons. Mahua oil cake and sugarcane jaggery are also piscicides. Some of the common ichthyotoxic plants are Safed Siris (Albizza procera), Nogdona (Artemisia vulgaris), Dar-hald (Barberis aristata), Banalu (Discorea sp.), Chaulmugra (Hydnocarpus hurzee), Akhrot (Juglans regia), Hazarmani (Phyllanthus urinaria), Kuchla (Strychonus nuxvomica), Sarphonka (Tephrosia purpuria), Ban Tambaku (Verbascum thapsus) and Timru (Zanthoxylum spp.)
3. Electrical fishing – Effect of pulsating electric field on fishes such as first reaction, electrotaxis (anode attraction), electro-narcosis and electrocution are utilized in electrical fishing equipment. Effect of electric field is also made use of in other fishing systems such as trawls and hook and line to enhance efficiency.