Autumn is the best time of the year to enjoy Chinese hairy crabs, and they are a common aquatic food product found on the local market. So, let us look into the growth and farming of Chinese hairy crabs scientifically in relation to rumours and concerns over recent years about the safety of eating these crabs, so that everyone can have a better understanding of safe consumption of Chinese hairy crabs.
Physiological structure
The Chinese hairy crab (Eriocheir sinensis), also known as Shanghai hairy crab, has conspicuous hairs on its claws, hence its name. These crabs are priced by their size and weight, so the larger the size, the more costly they are. They are known for their delectable meat, and the autumn harvest season is the best time of the year to savour their “crab mustard” and “crab fat”. “Crab mustard” refers to the ovaries and egg cells of female hairy crabs, which appear as a granular orange-reddish mass upon steaming. The “crab fat” consists of the seminal vesicles and reproductive organs of male hairy crabs, which becomes white, translucent and viscous upon steaming. There is a popular saying of “females in September and males in October” when it comes to savouring Chinese hairy crab. It means it is best to eat the female crabs in the 9th month of the lunar calendar, and male crabs in the 10th month, owing to the difference in sexual maturity and reproductive period between males and females. But both males and females have a yellowish-orange paste-like mass, which is their hepatopancreas, in addition to their reproductive organs commonly known as “crab mustard” or “crab fat”. As the hepatopancreas are connected to the reproductive organs, they are often mistaken as part of the “crab mustard” or “crab fat”.
Behaviour and habitats
The aquaculture conditions have a great influence on the quality of Chinese hairy crabs. The farmed hairy crabs would be of fine quality only if they live in an environment with favourable conditions. This is why the hairy crabs produced in certain regions are particularly famous and are very popular, since they were bred in suitable conditions and have plump and delectable meat. The hairy crabs inhabit the mud banks of rivers and lakes, in burrows in intertidal zones, under gravel and aquatic vegetation, and are omnivorous. Though plants and plankton are their main food sources, they also feed on the dead bodies of other animals, and even egg masses found in the abdomen of members of the same species. Once they enter a non-native habitat, their foraging behaviour is likely to cause ecological harm to the new area, so they are often considered as an invasive species.
Nowadays, Chinese hairy crabs are mostly farmed, since the cultivation environment, including quality of water, feed, mud in river bottoms or clays, can be well-controlled in aquaculture farms to greatly improve their quality and safety for consumption. Conservation of the ecological environment, water quality and the land, as well as pollution control, is vital to the production of aquatic food products intended for human consumption. In China, all fishing and aquaculture activities must comply with the “Fisheries Law of the People's Republic of China”, “Regulations on the Administration of Quality and Safety of Aquatic Products” and other relevant regulations to ensure the quality and safety of aquatic food products. With respect to the hairy crabs exported to Macao, the authorities overseeing food safety and quality in Mainland China have imposed a series of stringent regulations in regard to the surrounding ecological conditions of hairy crab aquaculture, remediation of pollution, the entire growth cycle of hairy crabs, disease prevention and control, the transportation of the exported hairy crabs, etc. They also carry out quality verification and testing of the hairy crabs for export to make sure the ones exported to Macao comply with the safety requirements.
Nutritional value
Chinese hairy crabs are low in fat and rich in protein and minerals, particularly calcium, phosphorus, potassium, iron, zinc and selenium. Despite being highly nutritious, their levels of cholesterol cannot be ignored. Every 100 grams of “crab fat” contains about 200 to 466 milligrams of cholesterol, and every 100 grams of crab meat contains about 135 milligrams of cholesterol. As recommended by the World Health Organization, a healthy adult should not consume more than 300 milligrams of cholesterol a day. For individuals with hyperlipidaemia, they should limit their cholesterol intake to no more than 200 milligrams a day. So, it is best to limit eating hairy crabs to one crab at a time, otherwise vascular health may be affected.
Inspection and quarantine measures taken by Macao on Chinese hairy crabs
The majority of Chinese hairy crabs sold in Macao is imported from Mainland China, and all of them must come from aquaculture farms approved for export by competent regulatory authorities of Mainland China. Source monitoring is conducted throughout the entire aquaculture process in the farms, with respect to water quality, sediment, crab larvae and crab feed, to ensure that the quality of hairy crab meets the specific requirements for export to Macao. Since 2017, the Municipal Affairs Bureau (IAM) has performed pre-inspection on Chinese hairy crabs coming from aqua-farms which directly supply these crabs to Macao, and has taken joint action with competent authorities of Mainland China to inspect these aquaculture farms, and streamline the inspection procedures to ensure the stable supply of Chinese hairy crabs to Macao.
Moreover, IAM has taken a series of actions to ensure the quality and safety of Chinese hairy crabs supplied to Macao. It maintains close contact with food safety regulatory authorities of Mainland China to understand the production and supply of the hairy crabs and communicate with food business sectors to collect the latest data on supply of Chinese hairy crabs in an organised manner. It also pays visits to food safety regulatory authorities of Mainland China for further information exchange on the supervisory system used in monitoring the production process of Chinese hairy crabs, and looks into the safety indices derived from testing for dioxins and nitrofurans in the crabs. By means of regional cooperation, it visits aquaculture farms which directly supply these crabs for Macao on a random basis to learn about the actual management, supervisory system and sales arrangement of Chinese hairy crabs so as to reduce the safety risks associated with the Chinese hairy crabs exported to Macao.
In addition, all fresh and live aquatic food products imported into Macao must be declared and subject to mandatory inspection in accordance with existing laws and regulations. Their importers are required to present the respective health certificates issued by the official authorities of their country of origin and provide supporting information on their health inspection for consideration and approval, which are important for ensuring the safety of consumers in eating Chinese hairy crabs.
What makes Chinese hairy crabs susceptible to contamination with dioxins?
In recent years, the samples of Chinese hairy crabs in neighbouring regions were found to have excessive levels of dioxins and have caused public concerns. Dioxins are environmental pollutants produced in forest fires, wildfires, combustion, incineration and various industrial activities. They can be found in the air, soil, rivers and lakes, and exist in the environment for a long time and are not readily biodegradable. Once they enter the food chain, they tend to accumulate in the bodies of plants and animals.
These pollutants tend to deposit in the sediment at the bottom of lakes, where water movement is slow. Since Chinese hairy crabs live in the benthic zone of lakes, they are susceptible to dioxin exposure owing to their habitats.
Maintaining a balanced diet and avoid eating limited types of food helps to reduce dioxin intake from dietary sources. It is also necessary to attach importance to environmental protection, control and reduce pollution as such actions are benefiting human health in the long run.
002/DIR/DSA/2021
