The Breeding and Production of Hilsa May Stop Due to River Water Pollution

 

Bangladesh is a riverine country and Hilsa is the national fish of Bangladesh. In 2017, Hilsa fish was recognized as a Geographical Indication or GI product of Bangladesh. According to Worldfish, 86 percent of the world's hilsa is produced in Bangladesh. It is very difficult to find a Bengali in the country and abroad who does not like hilsa. Hilsa is truly unmatched in taste and quality. Both the sea and the river are the breeding grounds of hilsa. In the past years, hilsa had almost disappeared, and in such a context, the breeding and production of hilsa has increased significantly due to various measures taken by the government, including the ban on mother hilsa hunting.

But the quality of water in Padma and Meghna rivers is gradually deteriorating in the breeding grounds of hilsa. At the same time, the amount of food required for hilsa is decreasing. Hilsa researchers say that this may have a negative impact on the breeding and production of hilsa. Hilsa production in the river has already decreased. One of the reasons is river water pollution. Government Fisheries Research Institute River Center in Chandpur has been testing the water quality for a long time in places where hilsa are found. The researchers of this institution monitor dissolved oxygen in water (DO-dissolve oxygen), pH, water and air temperature, hardness (alkalinity), ammonia content etc. every year. Fisheries experts say that pollution in the aquatic environment is harmful to any fish. However, hilsa is a very sensitive fish and hilsa cannot take small changes in environment due to pollution. Hilsa can change its course. An increase in ammonia in the water can alter the food requirements of hilsa.

Dissolved oxygen or DO is one of the regulators of water quality in Hilsa range. If the DO content is less than five milligrams per liter, it is considered less suitable for the aquatic environment. Research has shown that DO values have declined in Padma over the past five years. The average value of DO in Padma water was 8.70 in 2018 and has been decreasing almost every year since then. DO value in 2022 was 5.41. The average value of DO in Meghna in 2018 was 8.40 percent and it decreased to 6.84 percent in 2022. Ammonia is a chemical compound composed of nitrogen and hydrogen, where the water quality is good, its presence should be zero. The average presence of ammonia in Padma water in 2018 was 0.4 percent and it was the same in last year. But the average presence of ammonia in Meghna water is 0.21 percent and it was 0.27 percent in the last year. On the otherhand, pH is a measure of acid and alkalinity. A pH of 7.5 to 8.5 but not below 7.0 is required for an aquatic environment. The average presence of pH in Padma river was 8 and last year it decreased to 5.47. Meghna had a pH of 8.13 in 2018 and water temperature in Padma increased from about 25 to 30 degrees between 2018 and 2022. At this time, however, the water temperature in Meghna decreased from 27.40 to about 27.

Researchers say that the habitat of hilsa is being destroyed due to river water pollution. This can be due to either environmental or water pollution. Because about 36 percent sand-mud was found in the stomach of hilsa. This means that there is sand and mud in the water. It is not their food. They filter water and eat but because there is sand and mud in the water, it is going to their stomach. But then it is not digested. Moreover, the mother hilsa is laying eggs at a young age and this is definitely a concern. Because when this fish spawns, it is not matured for normal reasons. Hilsa researchers have advised the government through the project to extract up to seven lakh tons of hilsa in the next two to three years. Doing more than this can affect the natural reserves that are available.

The mother hilsa generally lays eggs twice a year, September-October (Bhadra month to mid-Kartik) and January-February (Mid-Poush to mid-Phalgun). However, the breeding rate is higher in the first season than in the second season. A mother hilsa lays a maximum of 1 to 2.3 million i.e. 10 to 23 lakh eggs at a time per season and takes care of the eggs all the time in the nursing ground. To save the newly hatched eggs from the hands of the enemy, it sometimes moves around with its mouth full. The care of the mother hilsa continues until the baby hatches from the egg and learns to swim. When they become suitable for swimming, the children swim with the mother hilsa and move around at will. Father hilsa also plays a role in raising hilsa baby. When the mother hilsa leaves the cubs to forage for food, the father hilsa looks after them.

Hilsa chicks grow from 12 cm to 20 cm in 6-10 weeks. Then call them Jatka. A jatka fish takes 1 to 2 years to develop into a full-fledged hilsa. It is 32 cm to 60 cm in size and 1 to 3 kg in weight. Jatka goes to the sea with Mother Hilsa. There, it turns into a full-fledged hilsa and returns to the river during breeding season. Despite all this care, only 10-20 percent of Jatkas get a chance to grow properly in the salt water of the sea. Because about 30 percent of the eggs are eaten by other fish and animals. 10 percent is lost early due to malnutrition. Later, about 20 percent were caught as Carp and 30 percent as Jatka in fishermen's nets. It is said that if even 50 percent of the eggs could grow properly, half of the different rivers and the Bay of Bengal would be occupied by hilsa.

Researchers say, due to water pollution and genetics, the size of hilsa caught in the country's rivers is gradually getting smaller. The size of the ovaries of fish is also getting smaller. It reduces the amount of eggs. Hilsa, born from the eggs of small fish, is also shriveled. Many of these fish lay eggs at a young age. Hilsa born from that egg is also small in size. The information of the Hilsa Research Strengthening Project says that the annual maximum sustainable production of Hilsa in the country's rivers and seas is 7.705 lakh metric tons. There is a danger of damaging the natural stock of hilsa if more fish are harvested than this. This will have a negative impact on hilsa breeding in the future.

Hilsa starts to leave the sea and come to the river during monsoon mainly for two reasons. One reason is food gathering, the second is breeding. The quality of river water plays a major controlling role in this arrival of hilsa. If the water quality is good, this movement of hilsa is unhindered, it is also more trapped in the fish net. Bangladesh is already in a vulnerable position due to climate change. Researchers say that if the temperature of the river water rises, it brings harm to the fish. Water pollution is relatively high in the upper reaches of Hilsa range in Padma and Meghna but lower down. Because industrial waste and polluted water along the banks of Buriganga and Shitalakshya rivers fall into the Bay of Bengal at low tide through Padma and Meghna. Meghna water pollution is relatively more than Padma. Buriganga, Shitalakshya and Turag are directly connected with Meghna. There are many factories on the banks of these rivers. Compared to that, the number of factories in the bank of Padma is less.

Any fish depends on the aquatic environment for food. Almost 42 percent of Hilsa's diet is algae and next is 36 percent sand or debris. Other foods include diatoms, rotifers, protozoa. The hilsa fish has a total of 27 species of plant particles and 12 species of animal particles in its diet. According to a study by the Fisheries Research Institute River Center in Chandpur, as compared to 2006, the food supply of hilsa has decreased by 6 percent as of last year. The breeding rate of hilsa in the river is decreasing. In the financial year 2016-17, the production rate of Hilsa in Padma and Meghna increased by more than 56 percent compared to the previous year. The next year this growth rate was about two percent and two and a half percent in 2018-19. But in the last year 2019-20, it decreased to 0.93 percent. According to a study by the Fisheries Research Institute, pollution is high in the upstream of the two rivers – Padma and Meghna, while production has also decreased in the upstream of the two rivers. In 2017-18, about 1,117 metric tons of hilsa was produced on the upper side of Padma. It decreased to 604 metric tons in 2020. In Meghna, hilsa production was 1,077 metric tons in 2017-18. After two years it increased slightly to 1,111 metric tons.

Hilsa production is increasing in the country, it is a comforting news because the hilsa researchers believe that the hilsa production is increasing due to efficient implementation of ban on fishing during breeding season. In 2018-19, hilsa production in the country was 5.33 lakh tons. In 2020-21, its amount was 5.65 lakh tons. But fisheries researchers think that water pollution can have a negative impact on this increase in hilsa production. River water pollution in the future may have a negative impact on the breeding rate of hilsa, the size of hilsa and its overall production. Various types of waste including industry are destroying the aquatic environment of hilsa. This waste needs proper management.

Hilsa researchers say that the course of hilsa depends on the rain. If the rainfall increases, the import of hilsa also increases with the increase of water in the river. The Protection and Conservation of Fish Rules 1985 has been amended and 6 Hilsa sanctuaries have been announced by the Ministry of Fisheries and Livestock. Besides, there are currently five breeding areas in the country. Recently, the new 5th breeding area of hilsa has been identified in the southern part of the country in Baleshwar river and estuary area with an area of about 7500 sq km. Earlier, four more breeding areas have been identified in the estuary area of Mayani-Meersrai, West Syed Awliya Point-Tajumuddin, Gandamara-Banshkhali and Lata Chapali Kalapara area. From Mirsrai of Chittagong to Lalmohan Upazila of Bhola is the largest breeding area of hilsa. Especially Manpura, Dhalchar, Balicharar, Moulvirchar - these are the biggest spawning points of hilsa. Chittagong, Bhola, Lakshmipur, Noakhali, Chandpur, Patuakhali, Barguna together in an area of about 7,000 sq km Hilsa fish lays the most eggs. Hilsa eggs are also laid in other rivers of the coast outside of it. In the six river areas that have been declared as hilsa sanctuaries, the production of hilsa has increased consistently. Hilsa sanctuaries are mainly located on the Meghna river and its basin and the confluence of Padma and Meghna. Among them, 100 km area of lower basin of Meghna river in Chandpur, 90 km area of Shahbazpur branch of Meghna river in Bhola, about 100 km area of Tentulia river are among these. Besides, 20 km area of Padma river, Hijla in Barisal, about 82 km area of Meghna river in Mehendiganj.

Every year March and April, during these two months fishing is prohibited in the said sanctuary. Fishing, selling, marketing, storage and transportation are strictly prohibited during this time. Unlike other fish, the hilsa does not require grass, hay, straw, husks or feed. There is no medical cost for hilsa, no need to import from abroad, nor is hilsa cultivated in ponds. Hilsa is our national fish. Hilsa only needs proper breeding, food assurance from natural sources and proper growing environment. Hilsa is a renewable natural resource and has immense importance in the country's economy. Moreover, hilsa is more sensitive than other aquatic animals and hilsa cannot accept small changes in environment caused by pollution. Therefore Hilsa may change its trajectory and this is definitely a concern for Bangladesh and for that, the concerned authorities should ensure that the river is free from pollution, only then the breeding and production of hilsa will increase.

 
Md. Zillur Rahaman is a
banker and a columnist.