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FWC Initiates Studies to Investigate Fish Health

Florida Fish and Wildlife Conservation Commission (FWC) staff, many of whom are avid anglers themselves, often use concerns expressed by stakeholders to spark new research and monitoring projects. Research studies on largemouth bass bed fishing, fish handling, and live-well conditions are just a few examples of anglers and biologists cooperating to reach a shared conservation goal.

Throughout 2019, Florida anglers reported fish with ulcers and tumor-like skin lesions to FWC using social media and the FWC Fish Kill Hotline. In response to these reports, biologists in the Freshwater Fisheries Research (FFR) and Fish and Wildlife Health groups (both part of FWC’s Fish and Wildlife Research Institute) developed and deployed a state-wide freshwater fish health monitoring program and a more comprehensive fish health survey for Lake Okeechobee.

Diseases and parasites are natural and occur throughout Florida lakes, the United States, and the world, even in the healthiest fish populations. Presence alone of diseases and parasites is not a sole indicator of ecosystem health.  In order to come to some conclusions of the overall health of a system many factors must be considered. Time of year, weather patterns, water management, cyanobacteria blooms, and many other factors can stress fish and lead to a range of fish disease conditions.  Consecutive years of standardized sampling will be required to establish trends in fish health.

Preliminary Report of State-Wide Field-Based Freshwater Fish Health Monitoring

45 lakes sampled during the Spring 2020

  • 15,428 largemouth bass collected by electrofishing
  • 5% of largemouth bass exhibited abnormalities state-wide
  • No correlation between percentage of fish with abnormalities and herbicide use

Fish health monitoring was incorporated into FFR’s Long Term Monitoring program’s 2020 spring largemouth bass electrofishing sample. Biologists externally examined each fish sampled for tumors, inflammation, sores, and other abnormalities and used the standardized fish health codes below to categorize fish with abnormalities.

CODE Fish Health Code (FHC) Description
B Animal with red or bloody areas
D Fish Dead prior to collection (mortality)
E Animal with scale loss or erosion (erosion = epidermis or dermis involved, muscle tissue not involved)
F Animal with fin erosion (fin rot = inflammation of fins, frayed fins)
M Mixed / unsorted sample
N Normal fish with no apparent abnormalities culled for baseline data
O Other (animal with conditions not specifically listed – describe condition in comments) (06/99) or animal with multiple abnormalities
P Animal with parasitic infestation
S Animal with skeletal malformation (vertebral, opercular, or fin deformities)
T Animal with raised area (tumor, cyst)
U Animal with depressed area (ulcer or lesion with inflammation, redness, swelling—muscle tissue involved)

Biologists examined 15,428 largemouth bass across 45 lakes in the Spring 2020.  On average, 5% of largemouth bass examined state-wide exhibited abnormalities (range 0 – 97% across lakes), of which parasitic infections were the predominant fish health condition.  There was no correlation between the percentage of fish with abnormalities and the amount of herbicide application.  For example, Lake Trafford receives minimal herbicide applications but largemouth bass exhibited the highest rate of abnormalities (97%) while fish in lakes such as Kissimmee, Toho, and Okeechobee that receive higher than average herbicide treatments, exhibited relatively low rates of abnormalities.  This is the first time that a large-scale state-wide effort has been made to assess fish health conditions across Florida’s lakes, but this is now part of the standardized process for sampling and will continue annually to provide trends in prevalence.

chart showing the number of bass sampled from lakes across the state and the percentage that had abnormalities

Preliminary Report of Lake Okeechobee Laboratory-Based Pathological Diagnostics

Biologists examined 718 fish in January 2020 collected by electrofishing

  • 19 fish that exhibited health abnormalities were pathologically diagnosed by fish health experts
  • Results included parasitic infections, bacterial infections, benign tumors, and cysts

Biologists collected 718 fish in January 2020 at Lake Okeechobee during our spring electrofishing survey.  All fish were examined externally and 19 fish that exhibited abnormalities were pathologically diagnosed by fish health experts from the Fish and Wildlife Health laboratory in St. Petersburg.  Fish health experts used standard necropsy procedures to examine fish including external and internal macroscopic and microscopic examination of the skin, gills, liver, spleen and kidney. They also fixed tissues for histology, a process similar to a biopsy, that microscopically evaluates cellular change.  Results of this health survey showed a range of diagnoses including parasitic infections, bacterial infections, benign tumors (papilloma and fibroma), and cysts.

Future Research

Going forward, biologists will continue to monitor fish health state-wide through field-based observations and conduct pathological diagnostics on fish collected with significant abnormalities.  Monitoring long-term trends in the prevalence of fish health abnormalities is critical to determine when there may be a concern.  We encourage anglers to report their account of dead or diseased fish to through the FWC Reporter App (preferred method), the FWC Fishkill Hotline: 800-636-0511, or submit a report online.

The FWC FFR section is working closely with the Aquatic Plant Management Technical Assistance Group to design and execute additional studies aimed at evaluating any potential effects of aquatic herbicides on fish health.  We are currently exploring independent laboratories that can analyze fish tissues and organs for the presence of aquatic herbicides.  FWC has already funded research through the University of Florida to analyze sediments in Lake Istokpoga for the presence of herbicides and found no legacy herbicides present demonstrating that herbicides degrade quickly after application.  Testing for the presence of herbicides in fish is the next step in this line of research. Additionally, we intend to conduct within-lake experiments where adult and juvenile largemouth bass are placed in cages and exposed to herbicide treatments to evaluate acute mortality and any impacts to fish health.  While there are many factors that contribute to fish health, we understand the concerns expressed by stakeholders about aquatic herbicides and are taking steps to address those concerns.