Enfermedades de peces

c) inmunidad

Many organisms that can potentially cause disease (known as pathogens) in fish are common throughout the marine/aquatic environment. Disease occurs when a pathogen (bacteria, virus or parasite) infects and multiplies within a host resulting in negative health consequences for and sometimes death to the host. For a pathogen to cause disease 1) the pathogen must be present in the environment and must infect the host 2) the host must be susceptible to infection and disease (as with all animals, healthy individuals are less susceptible to disease) and 3) the environment must be conducive to the presence and growth of the pathogen in the host organism. Thus, even if a pathogen is present, individual fish may become infected, but not develop disease.

As well, a pathogen may be the primary cause of disease or may be secondary to (the result of) an underlying condition. For example, gill damage as a result of plankton blooms may leave a fish susceptible to secondary bacterial infection.

For farmed salmon, health is managed at a population level rather than on an individual basis as disease in one individual does not necessarily result in disease in the population. As such, one or a few fish may test positive for a disease, but mortalities in the population will remain low if the disease is not prevalent throughout the population.

In addition to disease, farmed fish mortalities can result from environmental causes (for example, toxicity or gill damage from plankton blooms), from mechanical damage (for example, rubbing against net pen structures and equipment during storms) and can occur when individual fish adapt poorly to the marine environment (called 'poor performers').

Mussels contra sea lice larva:

Ian Bricknell, professor at UMaine’s School of Marine Sciences, said Wednesday that researchers have collected blue mussels from the Maine shore and found larval sea lice in their stomachs and intestines. This discovery, he said, could prove beneficial to not only the state’s farmed salmon and lobster industries, but to other commercial fisheries as well.

“It’s a very exciting piece of work,” Bricknell said of the research. “It’s a huge benefit.”

Bricknell said researchers plan to test the effectiveness of using mussels to combat sea lice by placing a fully loaded mussel aquaculture raft at an undetermined salmon aquaculture site in Washington County sometime this summer. The mussels will be attached to ropes that hang down 15 feet into the water, which he said is the maximum depth at which sea lice are commonly found.

Bricknell said that, if the mussels prove effective, a ring of mussel rafts could be placed around a group of salmon pens, effectively shielding the fish from sea lice. To round out the site’s productivity, he said, seaweed could be cultivated in a larger area surrounding the mussel rafts. Seaweed growth is enhanced by nitrogen and phosphates that are found in salmon effluent, he said. Seaweed has applications in the pharmaceutical and biofuel industries, he said, or like the mussels and salmon, could be cultivated for human consumption