Technology has temperature.
Text | Gong Xiaoli Wang Anyi
Last year, in the midst of public opinion, domestic rainbow trout ultimately failed to "climb" with salmon, an important reason is that rainbow trout is a freshwater fish, if eaten raw there is a risk of infection with parasites. However, many people do not know that the authentic salmon that grow in the depths of the ocean are also suffering from the existence of a terrible parasite. In the past 40 years, human beings have exhausted all kinds of high-tech means, and they have not yet found a way to completely defeat the parasite.
In the waters of the North Atlantic, hundreds of salmon are swimming back and forth in huge cages, and as they pass by a giant cylindrical machine, they occasionally trigger beams of green light.
This is certainly not a salmon disco, but a high-tech pest control tool that applies artificial intelligence and cutting-edge optics – the cylindrical machine is actually a robot equipped with two stereo cameras and a processor for running image recognition software, and once the machine focuses on and identifies the parasite on the surface of the salmon, it uses a medical diode laser (this laser beam is often used for ophthalmic surgery and hair removal) to quickly kill the parasite with a laser pulse of 100 microseconds.
This gelatinous, egg white-like viscous parasite is called sea lice. Over the past 40 years, sea lice have ravaged regions such as Norway, the United States, Canada, Chile and Scotland, causing at least a billion dollars a year in the global salmon farming industry.
This is a small marine parasite that looks a bit like Xiao Qiang when you look closely, and its reproductive ability is not inferior to Xiao Qiang — female sea lice can lay thousands of eggs in their lifetime, and after hatching, they go with the flow and gradually develop into infectious copepod larvae, as long as they can find salmon as a host within 20 days, they can continue to develop and reproduce.
Sea lice are particularly fond of Atlantic salmon, which parasitize on the surface of the salmon, suck on their mucus and epidermal tissue, and develop into mature sea lice in a matter of weeks.
Sea lice parasitism can induce stress responses in salmon fish, resulting in reduced salmon activity and easy prey on predators. In addition, wounds left by sea lice are susceptible to infection and dehydrate salmon because of the higher salinity of the sea, which will cause salmon to die under osmotic stress.
Since the rise of Nordic salmon farming in the early 1970s, sea lice have considered salmon as their primary host. The high density of salmon creates the perfect place for sea lice to breed and grow – the denser the salmon in the cage, the more active the sea lice.
In the late 1970s, farmers discovered that dichlorvos could kill sea lice without significantly affecting salmon, and the amount of chemical residues in the fish meat was lower than the test standard, so they began to use dichlorvos preparations to control sea lice. By 1989, however, the effect of this method was much less effective than before. A joint survey by the Scottish Salmon Farming Association (SSGA), the Institute of Aquaculture (IOA) and the University of Stirling confirmed that "some individuals of sea lice have decreased sensitivity to organophosphates", that is, sea lice have developed resistance.
In addition, due to the negative impact on the environment, the use of chlorhex is also severely restricted by the environmental protection department.
About 10 years ago, marine harvest, the world's largest salmon fisheries company, began using fish feed containing methylamino avermectin benzoate, a chemical that can pass through the inner wall of a fish's intestines and enter its tissues, while sea lice die immediately after absorbing the chemical. But the company's CHIEF EXECUTIVE, ALF Helge Aarskog, found that soon the sea lice developed resistance again.
Last year, a variety of salmon on the German market were detected through drug residue testing, and 4 out of 6 samples were heavily contaminated with ethoxyquinoline. Ethoxyquinoline is released as an antioxidant in aquaculture waters, which has toxic side effects on humans. Ethoxyquinoline has been banned, but the transition period continues until 2020. Therefore, until 2020, ethoxyquinoline residues will continue to be a major problem for salmon farming in Norway.
In addition, the commonly used lice remover drugs in salmon are: benzoylurea, insecticide, fluorourea, methylpyridinphos, pyrethroids, cypermethrin, cypermethrin...
Roundfin fish
People have also tried pollution-free means, such as biological deworming. There are several species of bulbophyllum and round-finned fish that, like cleaners, can eat sea lice from salmon. The problem is that fishing for rump fish also has unpredictable effects on marine ecosystems – bulbophyll fish eat sea urchins, and fewer bulging fish, more sea urchins. The addition of sea urchins can harm the seaweed forests on the seabed, and many other fish, including cod, need seaweed forests as shelters.
Eventually, aarskog began experimenting with laser robots to kill sea lice, but Norwegian farm owners were still not satisfied with this high-tech weapon, because robots could not remove sea lice under the gills and fins of salmon like cleaning fish...
A cage called an "egg"
Aarskog is also experimenting with other options, investing tens of millions of dollars in developing a spherical cage made of solid polymer walls. These cages, known as "eggs", are currently just prototypes, capable of holding 200,000 salmon and not receiving any parasites. However, the technology is expensive and complex, and is still in the testing phase in the laboratory.
Today, with a lot of money invested in "sea lice control" research, Researchers in Norway are about to complete the sequencing of the sea lice's genome by looking for weaknesses in sea lice and trying to study vaccines. Recently, the Scottish aquatic company Landcatch announced that it will sell genetically selected salmon eggs, which are said to come from salmon that is most resistant to sea lice infections. However, the researchers also admit that it is too early to get rid of this parasite completely ...
At present, drugs are still the most effective method of controlling sea lice in salmon farming, which returns to the problems of drug resistance and environmental pollution mentioned above. Now, do you still think that maricultured salmon is a pollution-free, natural and suitable food for raw food?