Category Archives: Fish and Wildlife Health

Fish and Wildlife Health Staff Investigate Ulcerative Skin Lesions in Lionfish

By Catalina Brown

In mid-August 2017, the FWC Division of Marine Fisheries Management’s lionfish group contacted the Fish and Wildlife Health Staff to confirm they collected lionfish (invasive Indo-Pacific lionfish Pterois volitans/miles complex) with significant ulcerative skin lesions approximately 30 miles off Pinellas County.

Ulcerated lionfish were also documented offshore Pensacola by local divers on Aug. 5. Following these initial reports, lionfish presenting with ulcers have also been reported in waters of the, East Florida Shelf, the Florida Keys, and the Bahamas as well as throughout the Caribbean Sea, including offshore of the Cayman Islands, Bonaire and Belize. FWC’s Fish and Wildlife Health group are collaborating with UF and Okaloosa County to obtain specimens and conduct necropsies to determine the etiology of the disease. In conjunction with UF, FWC have evaluated the specimens for parasitic infection as well as bacterial, fungal and viral infection.

This ongoing research is critical because the pathogen could be non‐specific and impact other marine sport fish species. Histological analysis has demonstrated tissues that appear to be healing. A causative agent has not been identified, but FWC continue to receive periodic reports of ulcerated fish and try to get specimens for analysis as they become available.

Gonad Staging

Photo Caption: Female in early developing oocyte with cortical alveoli. It is indicative of the transition from immature to mature in the
reproductive cycle.

By Catalina Brown

The FWH group’s research project, Monitoring Offshore Reef Fish Populations, includes a comprehensive gonad staging section. Gonad staging is incorporated along with a series of other organosomatic indices which will then be applied to increase knowledge of the overall health status of specific fish species. Organosomatic indices in fish can be modified by environmental stressors, nutrition, reproduction and age. Our objective is to assess reproductive maturation, distinguish groups between males, females and transitional hermaphrodites and eventually compare health indices between fish in the same phase of reproductive maturation to identify implications of life history.

We assigned two distinct phases for males: developing/regenerating and spawning capable. Females are multifaceted, and undergo several phases of maturation. Therefore, females are categorized as immature or mature, and mature females can be further divided into three distinct sub-phases: developing, spawning capable or regressing. These phases are based on morphological changes that occur through development. Health indices of fish that are of the same sex and reproductive phase will be compared to determine if individuals at each stage are allotting a comparable proportion of energy towards reproduction.

The relationship between Organosomatic indices and gonad developmental phases will eventually provide a clear correlation between life history and overall fish health.

A Tale of Two Teams: Coordinated Harmful Algal Bloom and Fish Kill Event Response

by Matt Garrett and Adam Richardson

dead fish on beach

In 2015-2016, a bloom of the red tide alga Karenia brevis and associated fish kills occurred in Northwest and Southwest Florida. Coastal blooms in both areas were first observed in September 2015. Although the Northwest bloom ended in January, the Southwest bloom endured until April 2016. Throughout this period, the bloom location and intensity, and associated local impacts including fish kills and reports of respiratory irritation, varied spatially from Pinellas to Monroe County. The extensive monitoring and response efforts required to track a bloom and its impacts of this spatial and temporal extent involved help from various groups within FWRI and other partners across the state, including an extensive volunteer monitoring network. Two events in particular involved careful coordination of FWRI’s Harmful Algal Bloom (HAB) and Fish and Wildlife Health (FWH) groups.

The first event occurred in late February, when extensive fish kills of marine species along the coastline of the Western Everglades were reported, several involving red drum, mullet, mangrove snapper, and snook. This raised concerns that a more extensive bloom of K. brevis, which had been previously observed at “medium” concentrations ranging from 105,500 – 473,000 cells per liter offshore of Pavilion Key (Monroe County), was causing the fish kills. Given the remote location of the reported fish kills, and the need for a rapid response to inform both management and stakeholders, scientists from the FWH and HAB groups designed a response plan utilizing two vessels to simultaneously sample both nearshore and offshore waters in the area impacted by fish kills. Staff obtained water quality data, water samples for phytoplankton, toxin, and eDNA analyses, deceased or moribund fish, seagrass samples, and sediments. Without the cooperation and rapid mobilization of the two groups, and the help of the Everglades National Park, timely samples from such a large area would not have been collected and analyzed. Although the bloom likely had a more northern origin, it is not clear what caused the fish kill. It is possible that a larger-scale bloom advected out of the system and was not detected at the time of sampling. It is also possible that either fish and/or cells may have been entrained or mixed within less saline waters, which can be detrimental to both marine fish and marine phytoplankton. For K. brevis, an influx of fresh water could contribute to cell lysis and subsequent release of intracellular toxins into surrounding water.

A second event occurred in early April, when FWC’s Fish Kill Hotline received numerous reports of a fish kill concentrated in Pinellas County, from the southern end of Madeira Beach to Indian Rocks Beach. Once again, FWH and HAB staff investigated. FWH staff conducted a beach survey, and experienced respiratory irritation in certain areas. Beachgoers were also impacted and FWH staff were approached several times with questions; they used this as an opportunity to obtain further information about the fish kill. Low densities of a variety of dead fish in early to late stages of decomposition, including hardhead catfish, spadefish, burrfish, toadfish, and grunts, were spread along the shore. Water samples from the shoreline confirmed “high” concentrations of K. brevis, ranging from 1.1 to 1.6 million cells per liter. HAB staff sampled coastal and offshore waters and in the fish kill area and further south, “medium” concentrations of K. brevis occurred in coastal waters. Cells were not observed further offshore. An autonomous glider was subsequently deployed offshore of Pinellas County through FWC and Mote Marine Laboratory’s Cooperative Red Tide program. The glider measures physical and biological parameters at different depths and its sampling track was programmed to facilitate continued surface and subsurface bloom tracking. Again, the collaborative efforts between FWH and HAB staff led to more comprehensive and spatially extensive sampling, and timely dissemination of information to stakeholders, and provided relevant contextual data to inform further response efforts at the time of the events, as well as our understanding of how these specific events occurred to improve monitoring and event response efforts.


by Catalina Brown 

Histology is a branch of anatomy used to study tissue structure and function in animals and plants.  Scientists use light and electron microscopes to analyze small sections of preserved tissue. Small pieces of tissue are fixed and embedded with paraffin or plastic, and thin sections are stained to identify parasites, bacteria and fungi or to find tissue abnormalities. Scientists also examine tissues to understand and describe pathological or other biological processes such as gonad development. Many FWRI groups, including Fish and Wildlife Health, Fish Biology and Shellfish Biology, use histology as an integral part of their research.  For example, histology has been used to determine the reproductive status of populations for decades. In 1991, the FWRI histology lab modified the periodic acid Schiff (PAS) metanil yellow (MY) stain to highlight different tissue components to determine reproductive stage of an animal.  This stain, which differentially colors cell components and accentuates contrast in tissue sections, provides sharp characterization of tissue morphology and is now used worldwide.  Histology is a critical tool used by scientists to study animal and plant disease and to evaluate the overall health of marine species that are important to Florida.

slides of cells
Trichodinella sp. parasite in the gill of a Red Drum – Sciaenops ocellatus. Figure A shows the parasite as seen under a wet mount used to examine fresh tissue with light microscopy. In figure B, the same parasite can be seen in gill tissue that has been processed for histology and stained with the PAS/MY stain. Photo credit: FWH staff.