During the Tuesday, Jan. 7 public meeting with the Pennsylvania Fish and Boat Commission on Tuesday, Jan. 7, the prevalence of blotchy bass syndrome within smallmouth bass in the Susquehanna and Juniata rivers was brought up.

Blotchy bass syndrome is hyper-pigmented melanistic skin lesions, which was first documented in the 1980s in the Hudson River in New York, and was first seen in Pennsylvania in 1986.

While it has been observed since 1986 in the Commonwealth, committee member Geoff Smith who gave the presentation regarding the syndrome noted that it was not something that came up locally until the 2010s.

“It really came to prominence locally in 2012 and it kind of set off the media attention with young-of-year smallmouth bass mortality,” Smith said. “We added it to our study of fish heal analyses we did in the field and keeping track of it to better understand what was going on.”

At that time, contaminants to various issues was blamed for the cause, but a wide range of environmental and fish health analyses was already in place.

According to pathology, aggregation of melanocytes in the upper two layers of the skin was to blame. It was non-cancerous and didn’t appear harmful, but it was unknown as to why.

“When we requested funding, it didn’t allow us to look specifically at this, so we linked it into other studies and used existing funding,” Smith said.

Water quality and temperature were issues that were brought up to a cause, and an experiment was conducted alongside Lock Haven University to take wild fish and move to a hatchery setting. It removed the water quality element. It helped to see whether that would make the blotches go away or not.

“We had fish that lost color and some that gained color. It was our first suggestion that the condition itself was transmissible. It was a disease, which was something we did not expect,” Smith said.

USGS started looking at affected and unaffected tissues, affected tissues had viral particles. Further analysis saw they were from a class known as adomaviruses, something that was relatively new in North America according to Smith during his presentation.

There was a slightly different virus in largemouth bass.

“We focused primarily on the Susquehanna and Juniata rivers and our catch data from 2012-22, roughly 10 years of survey data was included in the analysis,” Smith said. “We looked at the presence and absence of melanistic activity.”

Physical and environmental variables were assigned to each fish in the survey. Bayesian hierarchical logistical regression models were implemented as well. That included random effects on site and year and fixed effects such as temperature and the total length interaction.

In total, 16,220 fish in the analysis, roughly 1,500 fish per year. There were 130 surveys at 20 sites and the overall prevalence was just under 3% (2.9%), or 471 fish of the 16,220 fish. Susquehanna did have a higher prevalence, however, with 5.0% seen compared to Juniata’s just 1.2%.

Sites for the Susquehanna River where fish were looked at and tested included Shady Nook, Port Trevorton, Liverpool, Clemson Island, Rockville, West Fairview, Dock Street, Turnpike, Goldsboro and Conowingo.

“We evaluated the condition by year, years are highly variable,” Smith said. “(There was) no clear trend, it was all over the place. In some years it’s higher or lower, and that variability also changes.”

Factors found associated were water temperature and fish length with a higher rate among colder water temperatures and larger, or longer, fish. With colder water temperatures, they are unsure if its physiological or behavioral.

For instance, is there a replication rate of the virus at lower temperatures? Smith noted that’s something they were unsure of at the current time.

“Fish in the winter will congregate into small areas, can they transmit it more easier than at other times of the year. We’re unsure of the mechanism, but these can all be related to it,” Smith said.

Most of the fish in the study were mature fish and started their spawning preparations for the coming spring.

The blotchy bass syndrome, however, was easily observed and the study can be used as a model for other conditions Smith noted. With those variables identified, they can focus on the mechanism.

“We can track it without being invasive to the fish and use it as a model to see how other viruses and pathogens transmit throughout a system,” Smith said. “We can focus more on the mechanism what’s causing it since we know what to narrow down and what conditions to look at.”

Smith noted that two papers were published on the topic, including one just a few weeks ago. The larger scientific community is being brought into this, not just within Pennsylvania, Smith noted.

Smith said that they were going to keep an eye on blotchy bass syndrome, but did note that the fish population was doing well overall.

“We continue to track reports that we get, it’s been going on long enough that people are becoming desensitized to it, so we don’t hear as much,” Smith said.

Regarding the Susquehanna River, there was a higher prevalence Smith noted in the North Branch.

“West (Branch) is relatively low, but we don’t see it as frequently there. North Branch is one of higher prevalence location, we’ve only seen at that more recently,” Smith said. “But we do our seeings there with higher prevalence in certain places. Juniata is lower for whatever reason, not sure why, but we see relatively low prevalence there.”