IV Workshop on Gonadal Histology of Fishes

Scientific steering commitee

- Fran Saborido-Rey, Institute of Marine Research (CSIC), Spain
- Nancy Brown-Peterson, University of Southern Mississippi, USA
- Jonna Tomkiewicz, DTU Aqua, Denmark
- Susan Lowerre-Barbieri, Florida Fish and Wildlife Research Institute, USA
- Hilario Murua, AZTI Tecnalia, Spain
- David Wyanski, South Carolina Marine Resources Research Institute, USA
- María A. Bruzón, Fishing and Aquatic Research Center, Spain

Sessions outline

Although actual gametogenesis is similar among all fishes, species exhibit a wide spectrum of reproductive strategies related to gametogenesis, including oocyte recruitment, timing of vitellogenesis, oocyte development and maturation, spermatozoa production and spawning pattern. Understanding the variations in gametogenesis may facilitate the comprehension of the reproductive strategy of the species. Of particular interest are the different histological features used to classify the reproductive strategy of teleosts, the methodology needed to assess gamete development (e.g. protocols for staining various cell components and structures), and the comparative analyses of those strategies in cold, temperate and warm water species.

Identification of fish in the immature and regenerating phases is often challenging without the use of histology, particularly as individuals approach the size/age at maturity.  Yet, there is little research focused on histological indicators to distinguish these phases.  Additionally, identification of skip spawning fishes relative to the immature and regenerating phases has received little attention. There are a number of histological features that can be used to differentiate these phases, but they differ among species and sometimes require specific histological techniques to be revealed.  Proper identification of these phases will impact the estimation of size and age at maturity outside the spawning season, resulting in important implications to stock assessment and management.

Most fish species show reproductive seasonality which is reflected by the timing of the onset of gonadal development, the duration of the spawning period, spawning frequency, etc. Seasonality may be connected with important behaviours, such as migration, or the development of sexual dimorphism. Assessment of seasonal patterns is necessary to identify the optimal time for sampling and seasonal fishing closures, or for the definition of marine protected areas. Fishing, through the alteration of stock structure, may also alter reproductive seasonality which can impact recruitment success.

The estimation of spawning frequency is of great interest in fish reproductive studies. Since postovulatory follicles (POFs) are the most common ovarian features used to estimate spawning frequency, it is necessary to age the deterioration and resorption processes of the POF with a series of distinct histological stages, such that each stage indicates the time elapsed since spawning. Proper identification and validation of the specific ageing key based on histomorphological classification of POFs is a pre-requisite for this type of study.

As the relationship between reproductive dynamics in fishes and sustainable fisheries is becoming increasingly clear, so too is the need for clear and concise terminology to improve communication and understanding among researchers.  This topic has been addressed at three previous workshops on the Gonadal Histology of Fishes and a conceptual model developed to identify and name the critical milestones or phases that occur within the reproductive cycle.  The phases are defined by the processes they represent, such as the beginning and ending of the spawning season.  Histological indicators for these phases are then identified for fishes representing a wide range of reproductive strategies and habitats, including teleosts and elasmobranchs. This session will focus on refinement of the newly developed reproductive phases terminology, particularly as it applies to freshwater, viviparous and hermaphroditic species. It will also address terminology used with the reproductive topics covered in the other theme sessions, such as that associated with reproductive strategies, skip spawning, and reproductive behaviour.