Bangladesh is a riverine country and hilsa is the national fish of Bangladesh. In 2017, hilsa fish obtained a geographical indication of Bangladesh. According to Worldfish, 86 per cent of the world’s hilsa is produced in Bangladesh. It is very difficult to find a Bengali who does not like hilsa. Hilsa is truly unmatched in taste and quality.
Both the sea and the river are breeding grounds of hilsa. In the past, hilsa had almost disappeared and in such a context, the breeding and production of hilsa has increased significantly because of various government measures, including mother hilsa closing season.
But the quality of water in the Padma and the Meghna is gradually deteriorating as breeding grounds of hilsa. At the same time, the amount of food required for hilsa is decreasing. Researchers say that this may have a negative impact on the breeding and production of hilsa. Hilsa production in the river has already decreased, majorly because of river water pollution.
The Government Fisheries Research Institute River Centre in Chandpur has tested the water quality for a long time in places where hilsas are found. The researchers monitor the dissolved oxygen in water, pH, water and air temperature, hardness or alkalinity, ammonia content, etc every year. Experts say that pollution of the aquatic environment is harmful to any fish. However, hilsa is a very sensitive and it cannot endure small changes in the environment caused by pollution. Hilsa can change its course. An increase in ammonia in the water can alter the food requirements of hilsa.
The dissolved oxygen is one of the regulators of water quality in hilsa range. If the dissolved oxygen content is less than five milligrams per litre, it is considered less suitable for the aquatic environment. Research has shown that dissolved oxygen values have declined in the Padma over the past five years.
The average value of the dissolved oxygen in the Padma water was 8.70 per cent in 2018 and has decreased almost every year since then. The value in 2022 was 5.41. The average value of the dissolved oxygen in the Meghna in 2018 was 8.40 per cent and it decreased to 6.84 per cent in 2022.
Ammonia is a chemical compound composed of nitrogen and hydrogen and where the water quality is good, its presence should be zero. The average presence of ammonia in the Padma water was 0.4 percent in 2018 and it was the same the past year. But the average presence of ammonia in the Meghna water is 0.21 per cent and it was 0.27 per cent in the past year. On the other hand, 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 the Padma river was 8 and in the past year, it decreased to 5.47. The Meghna had a pH of 8.13 in 2018 and water temperature in the Padma increased from about 25 to 30 degrees between 2018 and 2022. At this time, however, the water temperature in the Meghna decreased from 27.40 to about 27.
Researchers say that the habitat of hilsa is destroyed because of river water pollution. About 36 per cent 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 as there is sand and mud in the water, it is going to their stomach. But then it is not digested. Moreover, the mother hilsa lays eggs at a young age and this is definitely a concern.
Because when this fish spawns, it is not mature for normal reasons. Hilsa researchers have advised that the government should extract up to seven lakh tonnes 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, in September–October or Bhadra–mid-Kartik and in January–February or mid-Paush–mid-Phalgun. However, the breeding rate is higher in the first season than in the second. A mother hilsa lays a maximum of 1–2.3 million eggs at a time a season and takes care of the eggs all the time in the nursing ground.
To save the newly hatched eggs, it sometimes moves around with its mouth full. The care of the mother hilsa continues until the babies hatch from the egg and learn 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 babies. When the mother hilsa leaves the cubs to forage for food, the father hilsa looks after them.
Hilsa grow from 12cm to 20cm in 6–10 weeks that are known as jatka or fries. A jatka fish takes 1 to 2 years to develop into a fully-fledged hilsa. It is 32cm to 60cm in size and 1 to 3kg in weight. Fries go to the sea with mother Hilsa and they turn into a fully-fledged hilsa and return to the river during the breeding season.
Despite all this care, only 10–20 per cent of fries get a chance to grow properly in the salt water of the sea. Because about 30 per cent of the eggs are eaten by other fish and animals. Ten per cent is lost early due to malnutrition. Later, about 20 per cent are caught as carp and 30 per cent as fries. It is said that if even 50 per cent of the eggs could grow properly, a half of the different rivers and the Bay of Bengal would be occupied by hilsas.
Researchers say that because of water pollution and genetics, the size of hilsa caught in the 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 shrivelled. Many of these fish lay eggs at a young age.
Hilsa born from that egg is also small in size. The Hilsa Research Strengthening Project says that the annual maximum sustainable production of hilsa in Bangladesh rivers and seas is 7.705 lakh tonnes. There is a danger of damage to the natural stock of hilsa if more fish are harvested. This will have a negative impact on hilsa breeding in future.
Hilsa starts to leave the sea and come to the river during the monsoon mainly for two reasons. One reason is food gathering and the second is breeding. The quality of river water plays a major role in this arrival of hilsas. If the water quality is good, this movement of hilsas is unhindered. It is also more trapped in the fish net.
Bangladesh is already in a vulnerable position because of climate change. Researchers say that if the temperature of river water rises, it causes harm to the fish. Water pollution is relatively high in the upper reaches of the hilsa range in the Padma and the Meghna but lower down reaches. Because industrial waste and polluted water along the banks of the Buriganga and the Sitalakkhya rivers fall into the Bay of Bengal at low tide through the Padma the and Meghna, the Meghna water pollution is relatively more than the Padma. The Buriganga, the Sitalakhhya and the Turag are directly connected to the Meghna. There are many factories on the banks of these rivers. Compared with that, the number of factories in the bank of the Padma is less.
Any fish depends on the aquatic environment for food. Almost 42 per cent of the hilsa diet is algae and the next is 36 per cent sand or debris. Other foods include diatoms, rotifers and 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 with 2006, the food supply of hilsa decreased by 6 per cent in the past year. The breeding rate of hilsa in the river is decreasing. In the 2016–17 financial year, the production rate of hilsa in the Padma and the Meghna increased by more than 56 per cent compared with the previous year’s figures.
The next year, this growth rate was about 2 per cent and 2.5 per cent in 2018–19. But in 2019–20, it decreased to 0.93 percent. According to a study by the Fisheries Research Institute, pollution is high upstream the two rivers — the Padma and the Meghna – while production also decreased upstream the rivers. In 2017–18, about 1,117 tonnes of hilsa were produced on the upper side of the Padma. It decreased to 604 tonnes in 2020. In the Meghna, hilsa production was 1,077 tonnes in 2017–18. After two years, it increased slightly to 1,111 tonnes.
The hilsa production is increasing is a comforting piece of news because hilsa researchers believe that the hilsa production is increasing because of efficient implementation of the ban on fishing during the breeding season. In 2018–19, hilsa production was 5.33 lakh tonnes. In 2020–21, it was 5.65 lakh tonnes.
But fisheries researchers think that water pollution can have a negative impact on this increase in hilsa production. River water pollution in 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 industrial wastes, 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 an increase in water in the river. The Protection and Conservation of Fish Rules 1985 has been amended and six hilsa sanctuaries have been announced by the fisheries and livestock ministry.
Besides, there are five breeding areas. Recently, the new fifth breeding area of hilsa has been located in the Baleshwar river and estuary area in the south. Earlier, four more breeding areas were identified in the estuary area of Mayani-Mirsarai, Pashchim Syed Awliya Point-Tazumuddin, Gandamara-Banshkhali and Lata Chapali Kalapara area. From Mirsrai of Chattogram to Lalmohan in Bhola is the largest breeding area of hilsa.
Especially Monpura, Dhalchar, Balicharar, Moulvirchar are the biggest spawning points of hilsa. Chattogram, Bhola, Lakshmipur, Noakhali, Chandpur, Patuakhali and Barguna together are where hilsas lay most of the eggs. Hilsa eggs are also found in other rivers of the coast outside of it. In the six river areas that have been declared 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 the Padma and the Meghna. Among them, 100km area of the lower basin of the Meghna river in Chandpur, 90km area of the Shahbazpur branch of the Meghna river in Bhola and about 100km area of the Tentulia river are among them.
Every year in March and April, fishing is prohibited in the sanctuaries. Fishing, selling, marketing, storage and transport are strictly prohibited during this time. Unlike other fish, hilsas do not require grass, hay, straw, husks or feed. There is no medical cost for hilsa. Hilsa only needs proper breeding, food assurance from natural sources and proper growth environment.
Hilsa is a renewable natural resource and has immense importance in the economy. That hilsas may change their trajectory because of river water pollution is definitely a concern and the authorities should ensure that the river is free from pollution