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projects > development of trojan y technology to control invasive fishes in the greater everglades > work plan

Project Work Plan

Department of Interior USGS GE PES
Fiscal Year 2012 Study Work Plan

Study Title: Development of Trojan Y technology to control invasive fishes in the Greater Everglades
Study Start Date: 1 October 2011
Study End Date: 30 September 2012, with possibility of future funding tied to progress
Duration: 12 months
Location (Subregions, Counties, Park or Refuge): The boundaries for this study are system-wide and include Everglades National Park, Big Cypress National Preserve, Biscayne National Park and various state and private lands.
Funding Source: GE PES
Other Complementary Funding Sources: USGS base funding of PI salary (Schofield)
Principal Investigator: Pamela J. Schofield, USGS, Southeastern Ecological Science Center
Study Personnel: Margaret Hunter, USGS, Southeastern Ecological Science Center
Supporting Organizations: USGS
Associated / Linked Studies: none

Overview & Objective(s):

Statement of Problem: Within Florida, dozens of foreign non-native fishes have established self-sustaining populations. There is concern that these introduced species could negatively affect native communities by predation, competition, or by serving as vectors for disease. The African jewelfish (Hemichromis letourneuxi) is known to be territorial, aggressive and predacious on native species. Its recent expansion across south Florida has caused concern, as it is effect on the native community is unclear. Neither is it clear to how stop or slow the spread of this invasive species. Methods to control/eradicate non-native fishes are critically needed, yet little work is being done on their development.

Specific Relevance to Major Unanswered Questions and Information Needs Identified: At present, the only management techniques available to control non-native fishes are physical removal (e.g., electroshocking), dewatering or ichthyocides. Unfortunately, all of these methods negatively impact native fauna as well as the targeted non-native fishes and require a great deal of effort (and therefore, funding). Herein, we propose development and testing of a genetic technique (Trojan Y) to control non-native fishes. Currently, the concept of using Trojan Y technology to control non-native species exists solely as a theoretical construct. Our project is the first to attempt application of this theory to the real world (in this case, the Greater Everglades). If we are successful in development of the technology, it could potentially be applied to a wide variety of species, including other fishes (e.g., brown hoplo Hoplosternum littorale), invasive applesnails (Pomacea spp.), the Australian red claw crayfish (Cherax spp.) and the green mussel (Perna viridis).


Species selection: We began this project by testing two candidate species: African jewelfish and Mayan cichlid (Cichlasoma urophthalmus). After developing techniques to breed both species in the laboratory, we decided to halt work on Mayan cichlid and focus on African jewelfish. Some reasons for this include:

F1 generation: In previous years we collected wild African jewelfish from south Florida, bred them in the lab (to produce the F1 generation) and feminized all the young. This resulted in a population of F1 females with a genetic makeup of either XX or XY (hereafter termed F1XX and F1XY).

F2 generation: We then bred ten F1 females to wild males, producing ten F2 broods. The broods from the F1XY females will contain the F2YY males, while the broods from the F1XX females are not useful to us. At this time, we cannot discriminate the F1XY females from the F1XX females, as they all look the same (phenotypically). We also cannot visually identify which of the F2 broods contain YY males (if any).

Planned Products:


  1. Breeding -- FY 2012
    1. Rear F2 broods to sexual maturity, determine male:female ratio for each brood.
    2. Continue refinement of laboratory breeding techniques; goals include:
      • increasing percent survival of each brood
      • decreasing generation time
    3. Breed several batches from wild-collected (i.e., non-treated) parents as a control; this will assist in determining male:female ratio of non-treated fish raised in our laboratory.
  2. Genetics -- FY 2012
    1. Develop sex-specific genetic markers (to differentiate F1XX females from F1XY females and to differentiate F2XY from F2YY males).
    2. Determine whether African jewelfish has an XY or ZW sex-determination system.

    These are big questions, and require attacking on several fronts simultaneously. To that end, we plan to:

    1. Continue our work with RAPD PCR techniques using random primers to locate sex-specific markers.
    2. Delve into more modern molecular technologies, such as sequencing.

    Once 4 and 5 are complete, we can:

    1. Test F1 fishes: keep F1XY females and discard all F1XX females
    2. Test F2 broods of F1XY females: keep YY males and discard XY males

    Then we go back to breeding . . . (this work will likely be completed in future years)

  3. Breeding
    1. Depending on the outcome of the wild-bred batches (3, above), we may need to do some work to look at temperature-dependence of male:female ratios.
    2. Breed F1XY females to F2YY males, then feminize the brood. Use genetic techniques developed in 4 (above) to differentiate F3YY females (keep) from F3XY females (discard).
  4. Future studies:
    1. Gynogenesis experiment -- can we create gynogens? This will allow us to confirm the XY or ZW sex-determination system as well as produce large numbers of YY males and YY females. However, it is very experimental and may require some time to complete. This step is NOT critical to the project, but would be helpful.
    2. Life history/Behaviour studies -- We would like to work closely to observe and quantify the life history and behaviour of YY females, comparing them to XX females. Some of the questions we would like to answer include:
      • What is the lifespan of YY females? Is it longer or shorter than XX females?
      • What is the fecundity and survival of broods from YY females?
      • What is the likelihood of males choosing to mate with YY females versus XX females?
      • What is the aggression level/social development of YY females? Can they pass as XX?
    3. Population-level studies -- We would like to conduct population-level studies here at our facility (either in ponds or mesocosm facility). I am working closely John Teem (Department of Agriculture and Consumer Serves, Tallahassee), who developed the theory of applying Trojan Y technology to the eradication of a population. I hope to continue partnering with him, especially in this phase when we conduct some small-scale population-level studies and compare our real-life results to his theoretical outcomes.