two women with fish

Sex in the Sea and Gonadal Histology 

by Laura Crabtree

Our reproductive dynamics group at FWRI is combining histological assessments of fish gonadal development with emerging issues in reproductive biology to better understand the complex systems involved in fish reproductive success and productivity.

men and women on boat with fish
The fisheries research group taking gonad biopsies from red drum, which were then released, several miles offshore of Tampa Bay.

Sue Lowerre-Barbieri leads our team of biologists with goals aimed at answering questions about the reproductive strategies of key fish species and how they are affected by fishing pressure. An important issue for us and other fisheries biologists has been the standardization of terminology and histological classification schemes so that we can make consistent and accurate comparisons among studies. Our collaboration in the scientific community, including other state and federal biologists along with academic experts at other institutions, have helped us advance this effort.

We currently study spotted seatrout, red drum, and seven reef fish species: red grouper, gag, scamp, red porgy, red snapper, vermilion snapper, and gray triggerfish.  Most of our reef fish gonad samples come from the West Florida Shelf Reef Fish Survey that Fisheries Independent Monitoring (FIM) has been conducting since 2008. They’ve collected over 6,000 samples from 86 species that have allowed us to develop baseline knowledge of where and when these species spawn and to create species-specific reproductive studies to estimate fecundity and reproductive behavior.

Our long term goals include the following:

Figure 1. Oocyte developmental stages on the left side with key histological indicators on the right side.
  • Mapping the spawning sites of target species by assessing where actively spawning females were collected
  • Assessing reproductive timing of these species by evaluating the season and time at which females of different reproductive phases are collected
  • Developing gonadal histology photographic reference guides for key species that include the histological indicators for determining reproductive state (Figure 1)
  • Publishing a fish reproductive histology atlas that can be used as a reference guide for biologists throughout the scientific community

drawing of fishOne of our most recent and exciting projects is a three-year Marine Fisheries Initiative (MARFIN) funded study assessing male abundance and factors affecting reproductive potential of gag, Mycteroperca microlepis, in the eastern Gulf of Mexico.

two girls on boat holding fish
Hayden and Jordie, two of our newest members, holding a gag during a data collecting trip in the Gulf of Mexico in 2016.

Our objectives are to determine their sex ratio; time of sex change; sex-specific differences in spatial ecology; and to evaluate the accuracy of sex determination methods (i.e. external pigmentation). The fish are caught by hook and line up to 180 miles offshore of Panama City. We also use a GoPro camera array to visually assess the relative abundance of fish and characterize habitat.

Overall, our results will provide additional data needed for stock assessments and result in improved management. We are collaborating on this project with FIM, Fish Health, Dr. Chris Koenig, and the National Marine Fisheries Service and will share the data with state and federal scientists.

Many of the species we study are hermaphroditic fish. There is reason to believe hermaphroditic fish are capable of changing sex quickly in response to instability in local populations so understanding this strategy and how fishing impacts it at the individual level as well as the population level are an important parameter in fishery management. Our reproductive dynamics group is developing expertise in understanding the complexities of sexual patterns such as social structures and the vulnerabilities they may have to fishing pressure.