Using canned salmon to study roundworms, scientists assessed changes in Alaska's marine ecosystem over four decades, revealing the impact of ecological health and environmental legislation. Alaskan waters are an important fishing ground for salmon. Scientists want to know how climate change is reshaping these food webs, which underpin the complex marine food webs that underpin this fishery. But finding samples from the past is not easy.
Label for a canned fish dealer in Seattle in 1921. New research uses canned fish from the past to shed light on the history of marine parasites. Image Credit: Freshwater and Marine Photo Library/University of Washington Library
Natalie Mastick, who is now a postdoctoral fellow at the Peabody Museum of Natural History at Yale University, said, "We have to really open our minds and creatively look at what can be used as an ecological data source. "
As a Ph.D. student at the University of Washington in Seattle, Mastic used an absolutely unorthodox source when researching Alaska's marine food web: old canned salmon. The cans contained four salmon fillets, all caught in the Gulf of Alaska and Bristol Bay, over a period of up to 42 years. Mastik and her colleagues dissected 178 canned fish fillets and counted the number of Anisakid nematodes, a common tiny marine parasite, in the fish.
These parasites have already been killed during canning and do not pose any danger to human consumers if consumed. However, counting roundworm populations is a measure of the state of marine ecosystems.
A highly degraded nematode found from canned salmon with a scale mark of 0.5 mm. Photo credit: Natalie Mastick/University of Washington
Chelsea Wood, associate professor of aquatic and fisheries sciences at the University of Washington, said: "Everybody thinks that having bugs in salmon is a sign that something is wrong. The life cycle of nematodes integrates many components of the food web. I think their presence is a sign that the fish on your plate are coming from a healthy ecosystem. "
In a paper published April 4 in the journal Ecology & Evolution, the team reported an increase in nematode presence in salmon and pink salmon from 1979 to 2021, while levels of couk salmon and sockeye salmon remained unchanged.
"The life cycle of nematodes is complex and requires multiple types of hosts," said Mastek, first author of the paper. Seeing their numbers increase over time, as we see in pink salmon and salmon, suggests that these parasites are able to find all the right hosts and reproduce. This may indicate that the ecosystem is stable or recovering, with enough suitable hosts. "
The Anisakids nematode originally lived freely in the ocean. When they are eaten by small marine invertebrates such as krill, they enter the food web. When the original host is eaten by other species, nematodes follow. For example, infected krill can be eaten by small fish, which in turn can be eaten by larger fish, such as salmon. This cycle repeats until the nematodes eventually enter the intestines of marine mammals, where they reproduce. The eggs are excreted back into the ocean to hatch and a new cycle begins.
De, a senior author of the paper, said: "Without a host – such as the marine mammal – Anisakids nematodes cannot complete their life cycle and the population declines. five
Photograph of the Anisakid nematode in red circle in canned salmon fillet. Photo credit: Natalie Mastick/University of Washington
Humans are overwhelmingly unable to be hosts for this nematode. Eating bugs from fully cooked fish poses little danger because the bugs have died. However, if the nematodes in raw fish or fish that are not fully cooked, also known as "sushi worms" or "sushi parasites" – are eaten alive in the stomach, they may cause symptoms similar to food poisoning or rare parasitic infections.
The Seattle-based Seafood Products Association donated the canned salmon to Wood and her team. The association no longer needs these cans, as they are set aside for quality control every year. Mastic and co-author Rachel Welicky, an assistant professor at Neumann University in Pennsylvania, experimented with different methods of dissecting canned fish fillets to look for nematodes. The worms are about a centimeter (0.4 inches) long and tend to be entrenched in the muscles of the fish. They found that by pulling the fillets apart with tweezers, the team was able to accurately count the number of worm carcasses with the help of a dissecting microscope.
There are several explanations for the rise in Anisakid nematode levels in pink salmon and salmon. In 1972, the U.S. Congress passed the Marine Mammal Protection Act, which allowed the populations of seals, sea lions, orcas, and other marine mammals to recover after years of decline.
"Anisakid nematodes can only reproduce in the gut of marine mammals, so this may indicate that numbers are on the rise during our study period – from 1979 to 2021 – as opportunities for reproduction have increased," Mastic said. Other possible explanations include warming temperatures or the positive effects of the Clean Water Act. "
The stable Anisakid nematode content in Cook salmon and sockeye salmon is more difficult to explain because there are dozens of species of the same species, each with its own range of invertebrate, fish, and mammalian hosts. While the canning process has preserved the shell of Anisakid intact, it has destroyed the softer parts of its anatomy that could have been used to identify individual species.
Mastic and Wood believe that this method can be used to study the parasite levels in other canned fish, such as sardines. They also hope that the project will help make new, casual connections that will lead to a better understanding of the ecosystem of the past.
"This study is because people heard about our research through the grapevine," Wood said. It is only by discovering untapped sources of historical data by networking and making connections that we can gain a deeper understanding of the ecosystems of the past. "
编译自/scitechdaily