The Bihar government has cautioned people against consuming unfamiliar fish that have entered the state with floodwaters from Nepal, warning that they may be contaminated and hazardous to health.

Bihar Fisheries Minister Nand Kishor Ram on Wednesday urged people to avoid eating these fish, which he said are "visibly distinct in their appearance" and are known to cause stomachache, vomiting and breathing difficulties. He also appealed to fishermen not to catch or sell such fish.

A comprehensive advisory was issued on Tuesday by the state's Department of Dairy, Fisheries and Animal Resources, advising people not to consume fish caught from floodwaters until environmental conditions return to normal and natural contaminants and pathogens subside. The advisory warned that fish washed out of ponds, rivers, lakes and reservoirs during floods can spread over large areas and may come into prolonged contact with open drains, dead animals and decaying matter, increasing the risk of contamination by bacteria, viruses and fungi.

According to the advisory, continuous exposure to pollutants can make the fish unsafe for consumption. It recommended seeking immediate medical help at the nearest health centre if symptoms such as vomiting, diarrhoea, abdominal pain, dizziness or breathing difficulty appear after eating such fish. It also advised reporting sightings of unusual fish to the local District Fisheries Officer or administration.

People in East and West Champaran districts, Gopalganj, Bagaha and Saran have reported catching "strange-looking" large fish in recent days, and some people are said to have fallen ill after consuming them. Reports suggest that unfamiliar fish species have been turning up in flood-affected areas as water from Nepal's Trishuli river flows into Bihar via the Gandak and Kosi rivers.

The advisory comes as floodwaters carry debris and other material downstream. Wreckage from collapsed bridges and damaged hydroelectric projects in Nepal, along with vehicles, household items and LPG cylinders from flooded villages, has been seen floating into Bihar's rivers. Human and animal remains washed downstream from Nepal are also adding to the risk of infection.

Health experts have warned that mixing of contaminated floodwater with drinking water sources could lead to the spread of diseases such as diarrhoea and cholera. Consumption of contaminated water and food could also increase the risk of typhoid, hepatitis A and E.

Nepal Police have issued a similar warning for residents there.

The department has appealed to the public to strictly avoid consuming unknown fish as a precautionary measure.