Implementing a Statewide Protocol for Monitoring Freshwater Fish Health

  • Sampling locations where fish health conditions were recorded across Florida. Triangles represent the center point of a waterbody were fish health conditions were assessed.

  • Example of a largemouth bass with a lesion on its gill operculum.

The health of Florida’s freshwater ecosystems and sportfishes has been catapulted into the spotlight by concerned citizens. Stakeholders commonly associate aquatic plant management and herbicide use on the degradation of Florida’s water quality and an apparent increase in fish disease. Freshwater fisheries biologists lacked data to evaluate these concerns. Therefore, FWC’s Freshwater Fisheries Research and Management divisions added fish health assessments into the established freshwater fish long-term monitoring program (LTM). Fish are checked for abnormalities in the field using standardized methods during electro-fishing sampling. Abnormalities were recorded into five categories while in the field. The “FLOPS” model was developed to aid in the standardization of fish coding across the state: F = fin rot/erosion, L = lesion (including, but not limited to sores, ulcers, tumors), O = other (abnormalities created by anglers, natural predators, or spawning stress, etc.), P = parasitic infections and S = skeletal malformation. The main objectives of data collections were to document and communicate the prevalence of observable abnormalities on freshwater fish.

Biologists examined 15,428 largemouth bass across 45 lakes in the Spring 2020, all of which were collected using electrofishing. Electrofishing is a common sampling technique used in fisheries research, where biologists use an electric field to temporarily stun fish. After the fish are stunned, researchers collect them with nets, work them up, after which the fish are safely released. Sampling generally occurs twice a year, January through May and October through December. Depending on the region, samples correspond to water temperatures and fish spawning. Each waterbody is generally sampled over the course of two months in spring and one month in fall within the previously state range of months. 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.

Abnormalities were noted in Spring 2020 and Spring 2021 at 64 and 68 lakes across the state of Florida, respectively. On average across both years, 6% of largemouth bass exhibited abnormalities, of which lesions (2.5%) were most prevalent during both years. In 2020, 18,519 bass were examined and 1,088 (5.9%) coded with some abnormality, while in 2021, 18,918 were examined and 1,072 (5.7%) were coded. Parasites (code P) were recorded most often in 2020 while lesions (code L) were the most recorded abnormality in 2021.

The percent of abnormalities was then compared to 39 variables from categories including herbicide use, water quality metrics, watershed land use, and fish community composition. A few specific variables were: the percent of urban land use by watershed, total pounds of applied active ingredient herbicide (i.e. glyphosate, diquat, 2,4-D) per surface acre, and total lake productivity or trophic state. FWC biologists found no evidence to support a link between any variables and the prevalence of abnormalities in bass.

This initial study demonstrated no relationships between the percentage of largemouth bass with abnormalities and a variety of physical, chemical and biological lake characteristics. Continued data collection will support future analyses of trends in the prevalence of abnormalities in largemouth bass and other freshwater species of sport fish. Future management efforts will focus on providing current, relevant information to citizen stakeholders on different abnormalities and their effects on the status of Florida’s freshwater.

This project was funded in part by the Federal Sportfish Restoration fund. FWRI’s Freshwater Fisheries Research team led this project, the Fish Health team, and the Division of Freshwater Fisheries Management.