The conference began on a poignant note with the posthumous election of Ian Whittington, who sadly passed away in October 2014, as a fellow of the ASP. Ian Whittington was a very prolific scientist whose main research focus was on the biology and ecology of fish parasites, in particular a group of ectoparasitic flatworms call the monogeneans. The monogeneans are a ubiquitous and diverse group of parasites, and some of them are major pests for aquaculture. He was also a great mentor and his research group took a holistic approach to studying parasites which considered multiple aspects of their biology including their structure, behaviour and ecology throughout the entirety of their life cycles. He is greatly missed by many.
|Photo of monogenean-covered kingfish by Kate Hutson|
The process involves briefly dunking an afflicted fish in a freshwater bath, then this system - which consist basically of a flatbed scanner, microscope, and special software - is able to scan through the resulting soup of fish scales, mucus, and parasites to not only detect and count the number of monogenean parasites present, but also identify what stage of development they might be at, based on various characteristics of their body. The system can process 260 parasite specimens in 90 seconds, allowing aquaculture managers to quickly ascertain the level of infestation and act accordingly.
As a follow up to Andrew Shin's talk, Kate Hutson, a researcher and senior lecturer from James Cook University, provided an overview about a monogenean parasite call Neobenedenia, a genus that is developing into a major aquaculture pest. There are six recognised species of Neobenedenia - one particularly precocious species is found all over the world, infecting many different types of fish - this is the species which causes major problems for aquaculture. This is a very adaptable parasite which is able to change its form depending on the host they end up on, thus genetically identical individuals can end up looking quite different depending on their host species. Studies using fluorescent dye to keep track of the parasites found that while they initially settle randomly on the body of their host, as they grow, they move to specific body parts. In particular they congregate around the fish's fins where they will find potential mates (this invokes a mental image of parasite orgies happening on fish fins). And it doesn't take Neobenedenia long to get to that stage - they can reach sexual maturity and start pumping out eggs at 10 days old, and if no one else is around, as hermaphrodites, they can simply self-fertilise for at least 3 consecutive generation without suffering any ill effects.This makes them a formidable obstacle for any aquaculture system. But there are potential treatments under development on the horizon, ranging seaweed extracts that inhibit embryonic development, and cleaner shrimps which can eat up these pesky parasites and their eggs.
|Photo of Austrolittorina antipodum by|
From these two snails alone, she discovered four new species of flukes, two of which are exclusively found in the banded periwinkle. She also examined the Australian periwinkle A. unifasciata (which confusingly is also called the banded periwinkle), in which she found four species of flukes, one of them happened to be Gorgocephalus sp., a species of parasite which is known from its adult form living in the gut of fish, but rest of life cycle and its other life stages were unknown prior to her discovery. These flukes do very nasty things to their snail hosts - causing them to lose their appetite and their gonads to shrivel away. They also compromise their ability to stay attached onto rocks and other surfaces, which is a big deal for snails living on the rocky shores. In mark-recapture studies, Katie found that infected snails were recaptured less often than their non-parasitised conspecifics, presumably because they were more likely to get swept off the rocks.
|Fluke cysts in the foot of a clam|
Through a series of studies which included assessing the parasite load of clams from commercially harvested sites to those from unharvested area, as well as placing caged juvenile clams from different sites, Sorrel found that clams at site subjected to commercial harvesting had over one-third higher infection load than clams from unharvested sites. It possible that commercial harvesting decrease the density of clams, less individual around to soak up and "dilute" the pool of parasites in the environment. She also performed experimental infection of clams at various doses of C. australis and found that after 3 months of being exposed to C. australis, infected clams have reduced shell growth, body condition, and foot length. Considering the ecological role that these parasites can play through their bivalve hosts, these changes can have potentially cascading effects on the rest of the ecosystem.
|Photo by NTNU |
Museum of Natural history and Archeaology
Throughout its life, the giant squid ends up acquiring a community of different tapeworm larvae, all of them go to different sharks, and ending up in the wrong host is a basically a death sentence for these tapeworm. So inevitable, success for one species can spell disaster for another. Haseeb found that there are at least four species of tapeworm which uses the giant squid as their ticket to the gut of their shark host - two of them infect skates, one infect porbeagle sharks, and one infect sleeper sharks. All these host species inhabit very different environments.
Giant squids start out life in more shallow waters, then moving to the open ocean as they grow into paralarvae. In such habitats, they are potential prey to skates (in the shallows) and porbeagle sharks (out in the open ocean), and presents tapeworms of such hosts an opportunity to complete their life cycle. But as the squid ages and moves into the deeper waters, the window of opportunity for those skate and porbeagle shark tapeworms closes. So as the giant squid matures, it literally sinks their chances of ever reaching their final host - while at the same time offers a glimmer of hope for another group of tapeworms - those that need to reach the deep dwelling sleeper sharks to complete their life cycle. The deep sea might be the final destination for the squid's life, but it is also the case for the tapeworms that parasitises sleeper sharks.
As a side note, I asked Haseeb if he also found any other parasites from the giant squid, in addition to tapeworm larvae. He replied that there were also some anisakid nematodes (which use marine mammals as a final host) and the larval stage of a fluke which infects sperm whales. But the role that giant squid plays in the life cycle of those parasites will have to be another story, another time...
Speaking of shark parasites, Part 2 of my Special Report on #NZASP15 will include more on shark parasites, the ups and down of parasite life cycles, networking in reptiles (and their parasites), and a re-examination of Toxoplasma gondii and its reputation for behavioural manipulation. Stay tuned!