There are no records of legal introduction of broodstock, says shrimp expert.
How erly mortality syndrome (EMS) came to Mexico is somewhat of a mystery, Donald Lightner, shrimp pathologist from the University of Arizona told IntraFish newspaper Fish Farming International in an exclusive interview, although he thinks it may have had something to do with post-larvae (PL) sources.
“There are no records of legal introduction of broodstock -- I know the guy that writes the permits -- so it had to have been some other way,” he said.
Several hatcheries were producing PLs for stocking at the time and [the spread of EMS] seemed to follow some of the dominant hatcheries," Lightner said. "First in Nayarit, then Sinaloa and then finally Sonora. And it didn’t hit every farm so maybe it made a difference where they got their PLs."
Lightner hopes his rapid diagnostic technique will help prevent the disease spreading elsewhere in Central and South America, and that a planned ‘dry out’ instigated by the Mexican shrimp farmers’ cooperatives at the end of this year will be done properly, so as to stop the pathogen spreading.
“It’s just whether or not they do it correctly,” he said. “If they keep some sentinels or something out there then it’s not going to work.”
Meanwhile, triggers for the condition are still up for debate. While there had been some evidence that pH levels in ponds were a trigger, Lightner is still unsure and is awaiting an answer from the US National Fisheries Institute on funding to test the theory himself.
"It seems to be worse when temps are higher," Lightner told FFI, but this is somewhat thrown by the conditions in Mexico -- which were cold enoughto trigger whitespot in many of the shrimp. "That kind of strongly suggests EMS isn't as influenced by temperature as much as we might have once thought," said Lightner.