Water Quality and Fish Health

Since 1983, the FWC has actively investigated the occurrence of mercury in Florida's freshwater and marine environments.

The data collected by the FWC over the last 25 years contributed to the recent publication, “Basic Guidelines for Eating Freshwater Fish”. This section of the DOH Health Advisory Brochure gives general advice on the safest species to eat and applies to all state waters. Women of childbearing age and young children are encouraged to eat up to one meal a week of bluegill sunfish, redear sunfish, or brown bullhead catfish. The general population can eat up to two meals per week of these same species, with the addition of redbreast sunfish. Three of these sunfish species are the most popular panfish throughout the state and brown bullhead is one of the most commonly harvested catfish species. As an agency that promotes recreational fishing, the FWC is happy to report that these species are very safe for consumption no matter where they are caught.

Many sources of natural and manmade mercury exist in the environment. Natural sources include volcanoes, mercury deposits in rock and oceans through a process similar to evaporation called volatilization. Human-produced mercury comes from waste incineration, coal-fired power plants, mining and smelting, and industrial processes including chlorine-alkali processing, cement production and pulp and paper production. In the 1950s, scientists recognized that manmade mercury pollution was contaminating food sources. Early studies indicated that fish and wildlife gathered significant amounts of mercury from their environment and certain aquatic bacteria converted mercury into a more toxic form called methyl mercury. When the bacteria that produce methyl mercury are eaten by the next organism in the food chain, they pass on the mercury, and as it moves up the food chain it increases in concentration. This process is called bioaccumulation. Top level predators contain the highest concentration of mercury because they consume high numbers of contaminated prey.

Such is the case in Florida’s freshwater ecosystems, where the highest concentrations of mercury occur in top-level predatory fish like Florida bass, bowfin, chain pickerel and gar. Because Florida bass are a popular food fish among anglers in Florida and they can bioaccumulate high concentrations of mercury, they have been the major focus of monitoring for mercury contamination in fresh water lakes and rivers. Fish species with typically high levels of mercury in marine ecosystems are also upper-level predators (i.e. tuna, mackerel, shark, snook, etc.).

In 1983, the Florida Fish and Wildlife Conservation Commission (FWC), the Florida Department of Environmental Protection (DEP) and the Florida Department of Health (DOH) started actively investigating the occurrence of mercury in Florida's freshwater and marine environments. This multi-agency effort has focused on surveying important marine and freshwater bodies and fish species throughout the state.

• FWC biologists collect target species.
• DEP scientists analyze fish tissue for mercury.
• DOH officials conduct risk assessments and issue fish consumption advisories.

Advisories for mercury in Florida waters have been issued since 1989. Florida's freshwater and marine fish are generally considered safe to eat; however, it is a good idea to review the current fish consumption advisories for specific advice on fish species or individual bodies of water. The advisories are not intended to discourage anglers from eating fish but should be used to choose fish lower in mercury while limiting consumption of some species of fish from certain waters.

Data collection for these health advisories begins each year by compiling a list of 50 to 60 lakes and rivers. Other FWC personnel or the public may also suggest new water bodies to be added and the sampling list may change throughout the year, as some areas are unsuitable for sampling due to lack of fish or access. Researchers at FWC created a seven-year rotating re-sampling schedule for previously sampled lakes and rivers. The schedule is designed to keep the data and associated consumption levels as current as possible. Seven years is also a rough estimate of the average lifespan of most fish; so it is assumed that the sampling will target fish from the next generation.

Biologists attempt to collect at least eight harvestable individuals of each targeted fish species in each water body. Fish are collected by electrofishing then put on ice and transported to the laboratory. Then, researchers determine total length, weight and gender and a sample of muscle tissue is taken. The tissue samples are then labeled, frozen and shipped to the DEP Chemistry Laboratory in Tallahassee for analysis. Once mercury results are returned to FWC, this data can be submitted to the Department of Health for creating consumption guides. When creating a consumption guide, the average mercury level for a species in a single water body is taken into account.

For more information from the Department of Health and other organizations monitoring Florida’s water quality and contaminants, check out the link below.

Fish Consumption Advisories

Implementing a Statewide Protocol for Monitoring Freshwater Fish Health

The Florida Fish and Wildlife Conservation Commission (FWC) values the health of Florida’s freshwater ecosystems and sportfishes and agency staff recently addressed concerns about fish health in response to stakeholder concerns. These stakeholders commonly attribute aquatic plant management and herbicide use to the degradation of Florida’s water quality and the apparent increase in fish disease. Until recently, freshwater fisheries biologists lacked data to evaluate these concerns and determine the appropriate course of action. In response, the FWC’s Freshwater Fisheries Research and Management divisions implemented standardized protocols to record fish health abnormalities into the established freshwater fish long-term monitoring program.

Abnormalities were recorded into five categories while in the field. The “FLOPS” model was developed to standardize fish coding across the state:

F = fin rot/erosion
L = lesion (including, but not limited to, sores, ulcers, tumors)
O = other (wounds created by anglers, natural predators, or spawning stress)
P = parasitic infections
S = skeletal malformation

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 Florida 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 Florida 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 Florida 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.