Seasonal Reproductive Cycles In
Florida Largemouth Bass

Timothy S. Gross, William E. Johnson, Trenton Schoeb,
Nancy D. Denslow, Carla M.Wieser, Jon J.Wiebe, and Denise A. Gross

USGS - Florida Integrated Science Center, the University of Florida,
and Florida Fish and Wildlife Conservation Commission

Introduction

• Numerous studies have demonstrated seasonal patterns for reproductive function, success and behavior in a wide variety of fish species, however, few studies have characterized seasonal patterns for endocrine parameters in fish.
• These endocrine parameters/biomarkers (i.e. sex steroids and vitellogenin) are critical factors for the control and regulation of reproductive cycles in fish.
• The characterization of seasonal reproductive and endocrine cycles in fish may be useful for the evaluation of different populations and the elucidation of the mechanisms controlling reproduction.
• Our efforts have focused on these seasonal characterizations and the identification of environmental effects through the application of critical endocrine biomarkers.

Objectives

• Conduct a year-long, seasonal, survey of a largemouth bass populations under controlled conditions to develop, validate and characterize seasonal profiles for several critical biomarkers.
  (Experiment 1)
• To utilize these biomarkers as an assessment of effects and mechanisms for populations of largemouth bass potentially impacted by environmental exposures to contaminants.  (Experiment 2)

Experimental Design

Experiment 1:  A year-long, seasonal, survey of largemouth bass was conducted on a reference, hatchery, site to characterize reproductive seasonal cycles and appropriate biomarkers.

Experiment 2:   An additional year-long survey of several impacted and reference sites in North Central Florida were surveyed monthly to examine reproductive function and potential relationships to environmental contaminants.

Reproductive Biomarkers

• Gonadal-Somatic-Index (GSI):  gonads as a percent of body weight.
• Sex Steroids:
• Estradiol: primary sex steroid for female fish, critical to egg growth and development.
• 11-keto-testosterone:  primary male sex steroid for many fish species, critical to spermatogenesis.
• Testosterone:  sex steroid precursor for both estradiol and 11-keto-testosterone.
• Progesterone:  sex steroid responsible for final egg maturation in female fish.
• Vitellogenin:  egg yolk protein produced by the liver in response to estradiol.

Experiment 1:  Design

• Adult largemouth bass (n= 10 male and 10 female) were collected from a reference, hatchery, pond monthly for one year.
• Fish were sacrificed and the body weight and length recorded.
• Gonadal tissues were collected, weighed for the determination of gonadal-somatic-indices (GSI) and a histological evaluation of sex and reproductive stage.
• Plasma samples were collected from each fish and analyzed for the biomarkers:  estradiol, testosterone, 11-ketotestosterone, progesterone, and vitellogenin.

Experiment 2:  Design

• Adult largemouth bass were collected from lakes Apopka, Griffin and Woodruff as well as from two reclaimed muck-farm sites: Knight Farm and Long Farm.
• Plasma samples were collected from approximately 20 fish (10 males and 10 females) monthly from each lake/site for one full calendar year. 
• Plasma samples were analyzed for estrogen, testosterone, 11-ketotestosterone and vitellogenin.
• Fillet samples were collected for 5 bass from each site and analyzed for pesticide levels.

Site Descriptions

• Lake Apopka:  Florida's fourth largest body of freshwater (12,500ha) and one of the state's most polluted lakes. Contaminants and nutrients have entered the lake from (1) agriculture, especially citrus and muck farms, (2) the Winter Haven city sewage treatment facility and (3) a major 1980 pesticide spill (dicofol, DDT residues and sulfuric acid) from the former Tower Chemical Company (EPA SuperFund site). (Impacted, highly contaminated)
• Lake Woodruff:  National Wildlife Refuge (890ha). Historically little or no agricultural or urban contamination. (Reference, control)
• Lake Griffin:  (3,800ha) Contaminants and nutrients have also entered this lake from (1) agriculture, especially from muck farms and (2) from Leesburg city sewage treatment facility. (Impacted, mildly contaminated)
• Knight Farm:  This lake/pond is a former muck farm (150ha) which was flooded in 1991 and stocked with largemouth bass in 1992-1993.  Little or no reproduction of bass has been detected within this environment. (Impacted, highly contaminated)
• Long Farm:  This lake/pond is also a former muck farm (350ha) which was flooded in 1991 and stocked with bass in 1993.  No reproduction of bass has been detected.  (Impacted, highly contaminated)
   

Experiment 1: Seasonal Cycles for Female Largemouth Bass

Experiment 1: Seasonal Cycles for Male Largemouth Bass

Experiment 1: Seasonal Cycles for Female Largemouth Bass

Experiment 1: Seasonal Cycles for Male Largemouth Bass

Experiment 1:  Seasonal patterns for GSI in Largemouth Bass

Experiment 2: Plasma Estradiol in Female Bass

Experiment 2:  Plasma 11-keto-testosterone in Male Bass

Experiment 2:  Seasonal Profiles for Estradiol in Female Bass

Experiment 2:  Seasonal Profiles for 11-keto-testosterone in Male Bass

Conclusions

• Bass exhibited seasonal increases in GSI, plasma sex steroids and vitellogenin during the spring (spawning) season.
• These seasonal endocrine cycles were, in general, synchronous between sites and strongly correlated to gonadal stage.
• These studies are the first to fully characterize the seasonal endocrine cycles for Florida largemouth bass.
• These data will be critical to assessments of natural populations and for potential environmental contaminant effects in largemouth bass.