Non-destructive sampling breakthrough explained
A discovery that should lead to the potential for fish farmers to conduct non-lethal on-site testing for a number of diseases is likely to transform how fish health is monitored at farm sites.
During his PhD at the University of Glasgow, Dr Mark Braceland stumbled across something that could potentially transform the way aquaculturists monitor the health of their stocks.
Called the SPR (Selective Precipitation Reaction), Braceland’s work – in collaboration with BioMar and Marine Harvest Scotland - serendipitously discovered that a buffer commonly used in colorimetric assays based on substrate activity was causing protein aggregation and thus assay interference. Though interference did not correlate with total protein concentrations rather the changes in plasma abundance of certain proteins during disease.
Fish Farming Expert had a chance to talk to Dr Braceland about his discovery and the potential applications for fish health.
“I was trying to use an established colormetric assay for ceruloplasmin to understand the acute phase response in Atlantic salmon infected with salmon alphavirus; but, what I found is that in diseased fish the optical density was changing, but it wasn’t attributed to the test. What was happening is that the buffer itself was precipitating the proteins in the plasma,” he said.
Braceland, now a research scientist at the Centre for Aquaculture Technologies Canada (CATC) in Souris, PEI, has an interest in disease pathogenesis and biomarker discovery in aquaculture.
Braceland said that two of the biggest issues for producers right now in terms of health monitoring is that 1.) they are only looking for presence of pathogens, and 2.) sampling is destructive.
“We look for the pathogens that elicit disease – that’s the only reliable tool that we have right now,” he said. “But with the SPR, now we have a tool that can serve as an early warning for pathology that is starting to occur, during the transition from infection to clinical disease.”
Braceland noted that often the presence of a pathogen is not indicative of disease occurring.
“Pathogens are not synonymous with disease. Often they appear ubiquitous, with the transition from infection to clinical disease poorly understood,” explained Braceland. “The perfect example is piscine reovirus (PRV) – in Scotland there is often presence without clinical HSMI – so in that case, just screening for the pathogen does not give the farmer adequate information on when best to implement disease management strategies, for example functional feeds.”
“When that infection becomes a problem is hard to detect using the tools that we currently have,” he said.
Braceland said that the second biggest problem is that - in most cases – disease monitoring involves euthanasia, so producers are sampling only a handful of fish from their stocks.
“We are never getting a representative population of the stocks,” said Braceland. “The health surveillance programs need to be more proactive in their approach. With the SPR, producers can sample a large number of fish that can be returned to their cage.”
Braceland also said that, by monitoring a larger sample size, the farmers will have a much more accurate understanding of when clinical diseases are starting to occur.
A broad range of opportunities
The first application of the method is likely to be as a test for the pathology caused by PD but Braceland said that the SPR may have potential applications.
“Its biggest potential is in other diseases in fish that cause severe inflammation and/or necrosis of tissues,” he said.
And, for Canadian producers, this might be very useful.
“For example, diseases that cause necrosis, lesions, or tissue breakdown, would theoretically be detected using the SPR,” he said, noting that the test needs to be validated first before knowing for sure.
“The reason that this test works is that its detecting pathology – pathology (during PD) is necrotic, there are a lot of lesions and general breakdown of tissues which causes a leaking of intracellular proteins that gets into the humoral system,” Braceland explained.
“And what appears to be happening, is that [intracellular proteins] have a differential stability in the buffer used for SPR - these proteins aggregate and more a turbid solution which you can see by eye.”
He said that this aggregation can be quantified, and the level of turbidity is highly correlated with pathologies occurring in different tissues.
“More severe pathology elicits a higher turbidity,” he said.
