Invasive parasite affecting San Marcos, Comal rivers

Parasite robs fish of ability to swim, according to researchers

The Comal River in New Braunfels.
The Comal River in New Braunfels.

SAN MARCOS, Texas – A parasite problem in the San Marcos and Comal rivers is coming to a head and is now threatening local endangered species.

The parasite, discovered in 2013, affects the fins and jaw joints of fish, effectively robbing them of their ability to swim, according to parasitologist David Huffman.

"Larvae that do not seek out the fins often end up encysting in the jaw, which stiffens the joint and prevents the mouth from closing. This interferes with feeding, and forces the fish to swim continuously to breathe," Texas State University graduate student Allison Scott said.

The Haplorchis pumilio can rupture gall bladders, hearts and other vital organs of infected fish and in some cases where the parasite doesn't kill the fish, it can cause blisters on the tail.

"Uninfected fountain darters I set out in cages in areas of Landa Lake where fountain darters occur acquired infections so fast that one of them died in a few days, and all of them would have been dead after a month of exposure to the lake water," Scott said.

The good news is humans are unlikely to contract the parasite because we cook our fish.

"On the other hand, if there are cats or dogs that are visiting fish cleaning stations, then it could become a veterinary problem," Huffman said.

Huffman said he'd already warned a local vet to be on the lookout for the parasite.

Read more on the parasite here.

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