Tainted water: Toxic waste, hormones, antibiotics pollute Bangladesh fisheries

The use of antibiotics in fish culture and hormones in artificial fish breeding bring into question the safety of Bangladesh’s food supply, as exposure to high levels of these substances can harm human and environmental health.

Research shows that 88 per cent of fish farmers do not have proper knowledge of antibiotics use, and 81 per cent are unaware of effective chemical dosages in fish farming. Image: WorldFish, CC BY-SA 3.0, via Flickr.

Bangladesh has recently achieved remarkable success in freshwater fish production due to its fast-growing aquaculture, securing third place in global freshwater fish farming.

The country produced more than 1.25 million metric tons of freshwater fish in 2020 while it was only 440,000 metric tons in 1980, according to the United Nations Food and Agriculture Organization’s 2022 report on global fisheries and aquaculture.

To increase fish production to meet the protein demand of its growing population, Bangladesh has been using antibiotics and pesticides in fish culture and applying hormones in artificial fish breeding, which makes its food safety questionable.

Bacterial, viral, fungal and parasitic diseases often hit aquaculture production in Bangladesh and that is why fish farmers regularly use aqua-chemicals like antibiotics and pesticides to cut disease burden in fish farming.

The aqua-chemicals are mainly applied to prevent and treat bacterial, fungal and parasitic diseases. Those are also used to improve water quality and increase the productivity of fish culture ponds or act as growth promoters.

Despite contributing to the growth and development of the aquaculture sector, the use of these chemicals has been criticised for the potential adverse impacts on the environment and human health as well.

2021 survey, conducted via face-to-face interviews with fish farmers in Rajshahi district of Bangladesh, found that farmers used nine active antibiotic ingredients in finfish rearing. However, most of the fish farmers (88 per cent) needed proper knowledge of aqua-chemicals and antibiotics, and 81 per cent were unaware of the effective dosages of chemicals in fish farming.

Many fish farmers in the study areas reported the indiscriminate use of chemicals. About 72 per cent of fish farmers were ignorant about the aqua-chemicals’ residual effects on the environment and human health.

As a result, this preliminary study suggested strictly monitoring the use of antibiotics, pesticides and other aqua-chemicals in aquaculture.

Antibiotics have harmful impacts. Fish farmers in our country indiscriminately use antibiotics in aquaculture. Once any farm is found using antibiotics and chemicals in aquaculture, we immediately stop its fish production.

Benoy Kumar Barman, senior scientist, WorldFish

The residues come from the aqua-chemicals transmitted through the food chain to the human body, which may have significant health implications, including neurological, respiratory, gastrointestinal and reproductive complications.

Also, the excessive use and misuse of antibacterial substances, and their presence as residues in foodborne organisms, would contribute to the selection of antimicrobial-resistant bacteria. The research said there was a potential ecological risk due to the residues of antibiotics too.

However, co-investigator of the research Anwar Hossain said they did not find a level of antibiotics concentration in culture fish that was risky to human health, suggesting conducting a further study on it.

The study revealed that the rapid increase in chemical use would pose a significant threat to aquatic species and human health since more than 80 per cent of people in Bangladesh consume fish as animal protein.

“Of course, antibiotics have harmful impacts. Fish farmers in our country indiscriminately use antibiotics in aquaculture,” Benoy Kumar Barman, senior scientist at WorldFish, told Mongabay.

Mohammad Habibur Rahman, chief scientific officer (fisheries inspection and quality control) at Department of Fisheries, said antibiotics have health hazards and that is why the department always asks farmers not to use antibiotics and chemicals in fish farming.

“Once any farm is found using antibiotics and chemicals in aquaculture, we immediately stop its fish production,” he said.

Hormone use in fish farming

Fish culture is gaining popularity among people in Bangladesh with increased demand. Since people are now doing the aquaculture business, the demand for fish seed is rising. Nowadays, 1,056 fish hatcheries produce about 98 per cent fish fry in the country. In 2020-2021, the total fry production in Bangladesh was 668,801 kilograms (1.47 million pounds).

These hatcheries have been applying induced breeding practices to increase fish seed production.

Induced breeding is a process where the fish, which do not breed in stagnant water bodies, will do so under the influence of stimulants or hormones injected into their bodies. This process of injecting stimulants, hormones or pituitary extracts into the brood fishes causing fish to spawn in a controlled condition out of the natural environment is called induced breeding or artificial reproduction.

A study published in the International Journal of Oceanography & Aquaculture in August 2022 revealed that hatchery owners use three types of inducing agents — pituitary gland, human chorionic gonadotropin and gonadotropin-releasing hormone analogues in the spawning of Indian major carps, Thai pangus (Pangasius sutchi) and other brood fishes.

Hormones in aquaculture are used for artificial reproduction and sex reversal. The hormone used in fish farming for sex reversal aims at the production of monosex populations to boost growth rate or weight gain.

The use of hormonal products in fish farming can have harmful consequences, such as potential risks to human and environmental health related to hormone-dependent parameters, according to a 2018 study.

In humans, the research showed, exposure to hormones can cause endocrine disorders, such as early puberty in children, advances in bone age, negative repercussions on growth, modification of sexual characteristics and cancer development.

“Yet, there is no study on the consequences of aquatic ecology if brood fishes die after injecting excessive hormones during artificial breeding,” Barman said.

Habibur Rahman said the department has already asked all hatcheries in the country not to use hormones in fish seed production as it harms humans and the environment.

Industrial effluents in open water

Bangladesh has witnessed rapid industrial growth in recent years, with 6,000 large and medium industries and 24,000 small ones. Those industries often release untreated waste and chemicals into open waters, including rivers, wetlands and canals. These wastes contain toxic chemicals and heavy metals like lead, mercury, cadmium, zinc, copper, chromium, iron and manganese.

Around 200 rivers in Bangladesh receive a large amount of untreated industrial waste and effluent daily. Still, these chemical wastes harm fish diversity and human health.

Barman said the untreated toxic sewage and chemical wastes are going to fish through its accumulation, which is putting human health at risk.

The contamination of water bodies allows these pollutants to accumulate in common fish and shellfish species, which are used as local food, recent research has shown.

These toxic heavy metals released in the aquatic environment may enter the food chain through biomagnification and may cause various health problems in humans and animals.

“Chemical pollutants, heavy metal being non-biodegradable, can be concentrated along the food chain, producing their toxic effect at points after far removed from the source of pollution,” according to the report.

The study stated that exposure to heavy metals has been linked to several human diseases like development retardation or malformation, kidney damage, cancer, abortion, effects on intelligence and behaviour and even death in some cases of exposure to very high concentrations.

This story was published with permission from Mongabay.com.

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