As the number of fish reproduction studies has proliferated, so has the number of gonadal classification schemes and terms. This has made it difficult for both scientists and resource managers to communicate and for comparisons to be made among studies. We propose the adoption of a simple, universal terminology for the phases in the reproductive cycle, which can be applied to all male and female elasmobranch and teleost fishes. These phases were chosen because they define key milestones in the reproductive cycle; the phases include immature, developing, spawning capable, regressing, and regenerating. Although the temporal sequence of events during gamete development in each phase may vary among species, each phase has specific histological and physiological markers and is conceptually universal. The immature phase can occur only once. The developing phase signals entry into the gonadotropin‐dependent stage of oogenesis and spermatogenesis and ultimately results in gonadal growth. The spawning capable phase includes (1) those fish with gamete development that is sufficiently advanced to allow for spawning within the current reproductive cycle and (2) batch‐spawning females that show signs of previous spawns (i.e., postovulatory follicle complex) and that are also capable of additional spawns during the current cycle. Within the spawning capable phase, an actively spawning subphase is defined that corresponds to hydration and ovulation in females and spermiation in males. The regressing phase indicates completion of the reproductive cycle and, for many fish, completion of the spawning season. Fish in the regenerating phase are sexually mature but reproductively inactive. Species‐specific histological criteria or classes can be incorporated within each of the universal phases, allowing for more specific divisions (subphases) while preserving the overall reproductive terminology for comparative purposes. This terminology can easily be modified for fishes with alternate reproductive strategies, such as hermaphrodites (addition of a transition phase) and livebearers (addition of a gestation phase).

Although incorporating detailed reproductive data into all stock assessments is not a practical goal, the need to understand how reproductive biology affects population productivity is being increasingly recognized. More research focused on reproductive biology—coupled with a shift towards a resilience perspective in fisheries science—is resulting in challenges to many long‐held assumptions; the emergence of important new issues; and identification of the need to improve data and methods used in reproductive studies. Typically, data for reproductive studies are based on an assessment of gonadal development, which is most accurately evaluated with histology. This special section of Marine and Coastal Fisheries contains contributions from a workshop on the gonadal histology of fishes that was held in Cadiz, Spain, during June 2009. These papers cover a wide range of species and reproductive topics while introducing improved and new histological techniques. In this introduction, we address the following needs: (1) to employ standardization, thereby improving our ability to conduct comparative studies; (2) to better understand patterns of gonadal development and spawning events over time; and (3) to move beyond the spawning stock biomass paradigm. We identify the contributions of special section papers to these topics and conclude by suggesting needs for future research and integration of reproductive data into both conceptual and quantitative models to better understand how reproductive performance affects population dynamics.

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The blue crab, Callinectes sapidus, which uses the copper-dependent protein haemocyanin for oxygen transport, lacks the ubiquitous cytosolic copper-dependent enzyme copper/zinc superoxide dismutase (Cu,ZnSOD) as evidenced by undetectable levels of Cu,ZnSOD activity, protein and mRNA in the hepatopancreas (the site of haemocyanin synthesis) and gills. Instead, the crab has an unusual cytosolic manganese SOD (cytMnSOD), which is retained in the cytosol, because it lacks a mitochondrial transit peptide. A second familiar MnSOD is present in the mitochondria (mtMnSOD). This unique phenomenon occurs in all Crustacea that use haemocyanin for oxygen transport. Molecular phylogeny analysis suggests the MnSOD gene duplication is as old as the origin of the arthropod phylum. cytMnSOD activity in the hepatopancreas changes during the moulting cycle of the crab. Activity is high in intermoult crabs and non-detectable in postmoult papershell crabs. mtMnSOD is present in all stages of the moulting cycle. Despite the lack of cytCu,ZnSOD, crabs have an extracellular Cu,ZnSOD (ecCu,ZnSOD) that is produced by haemocytes, and is part of a large, approx. 160 kDa, covalently-linked protein complex. ecCu,ZnSOD is absent from the hepatopancreas of intermoult crabs, but appears in this tissue at premoult. However, no ecCu,ZnSOD mRNA can be detected, suggesting that the protein is recruited from the haemolymph. Screening of different taxa of the arthropod phylum for Cu,ZnSOD activity shows that those crustaceans that use haemoglobin for oxygen transport have retained cytCu,ZnSOD. It appears, therefore, that the replacement of cytCu,ZnSOD with cytMnSOD is part of an adaptive response to the dynamic, haemocyanin-linked, fluctuations in copper metabolism that occur during the moulting cycle of the crab.

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Exposure to oiled sediments can negatively impact the health of fish species. Here, we examine the effects of chronic exposure of juvenile southern flounder, Paralichthys lethostigma, to a sediment-oil mixture. Oil:sediment mixtures are persistent over time and can become bioavailable following sediment perturbation or resuspension. Juvenile flounder were exposed for 32 days under controlled laboratory conditions to five concentrations of naturally weathered Macondo MC252 oil mixed into uncontaminated, field-collected sediments. The percent composition of individual polycyclic aromatic hydrocarbons (PAHs) of the weathered oil did not change after mixing with the sediment. Spiked exposure sediments contained 0.04-395mg/kg tPAH50 (sum of 50 individual PAH concentration measurements). Mortality increased with both exposure duration and concentration of sediment-associated PAHs, and flounder exposed to concentrations above 8mg/kg tPAH50 showed significantly reduced growth over the course of the experiment. Evident histopathologic changes were observed in liver and gill tissues of fish exposed to more than 8mg/kg tPAH50. All fish at these concentrations showed hepatic intravascular congestion, macrovesicular hepatic vacoulation, telangiectasia of secondary lamellae, and lamellar epithelial proliferation in gill tissues. Dose-dependent upregulation of Cyp1a expression in liver tissues was observed. Taxonomic analysis of gill and intestinal commensal bacterial assemblages showed that exposure to oiled sediments led to distinct shifts in commensal bacterial population structures. These data show that chronic exposure to environmentally-relevant concentrations of oiled sediments produces adverse effects in flounder at multiple biological levels.

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Tilapia (Oreochromis spp.) were collected seasonally from four contaminated rivers in southwestern Taiwan for studies of morphological deformities that could be used as biomarkers of contamination. Morphological deformities found in tilapia were separated into 15 categories. Overall, the prevalence of deformities such as split fins, lower lip extension and gill deformities were significantly related to various water quality parameters, including low DO and high ammonium, lead and zinc concentrations. The persistence of tilapia in polluted waters and the development of a suite of morphological deformities suggest that tilapia can be used as sentinels of non-point source pollution in rivers.