Essential fatty acids are necessary for growth, survival, and development of larval fishes, but there is limited information on the essential fatty acid requirements of larval southern flounder (Paralichthys lethostigma). The objectives of this study were to elucidate connections between dietary supply of docosahexaenoic acid (DHA) and arachidonic acid (ARA) and deposited fatty acids in the head or body, and then link diet and stored fatty acids in the head or body with larval quality traits. From 4-15 days posthatch (dph), southern flounder larvae were fed rotifers enriched with four different combinations of DHA-rich Algamac 3050 and ARA-rich Algamac ARA. Fatty acid concentrations in the head and body were measured at 15 dph, and relationships between fatty acids in head or body and in the diet were determined. Larval quality traits, including specific growth rate (SGR), survival, and eight behavioral performance variables were measured. Results showed that concentrations of DHA and ARA in the head and in the body were correlated with concentrations of DHA and ARA in the diet. Growth rate did not vary among the four diets, but survival was positively correlated with the amount of lipid in the diet. Responsiveness to a visual stimulus was positively correlated with the concentration of DHA in the diet, the ratio DHA:EPA in the head, and total energy content of the diet. Turning rate during routine swimming was correlated with body DHA. This study demonstrates the influence of DHA content, total lipid content, and energy levels in the diet of southern flounder and provides a foundation for future studies examining causal factors of recruitment variability or larviculture production success. / text

The overall goal of this research was to verify the involvement of membrane progestin receptor alpha (mPRα) in mediating progestin-stimulated sperm hypermotility in the Atlantic croaker and southern flounder. Sperm motility in Atlantic croaker and southern flounder were tested with both the endogenous progestin, 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) or the selective mPRα agonist, 10-ethenyl-19-norprogesterone (Org OD 02-0). In croaker, the Pi3k/Akt/Pde and ErbB2/Mapk intracellular signaling pathways were examined. The role of mPRα in mediating sperm hypermotility and fertility in southern flounder was also studied. The effects of seasonal hypoxia on sperm motility in croaker were investigated in a field study in the northern Gulf of Mexico in the fall of 2010. Finally, the effects of acidified activator solution (simulating ocean acidification) were studied in the laboratory. In vitro, Org OD 02-0 mimicked the stimulatory actions of 20β-S in inducing sperm hypermotility and intracellular signaling cascades in croaker and flounder sperm, indicating that mPRα is the mediator of progestin signaling in the sperm of these species. In croaker sperm, both the Pi3k/Akt/Pde and ErbB2/Mapk intracellular signaling pathways were shown to be important mediators of progestin-induced sperm hypermotility, suggesting novel functions of G [subscript olf] βγ-subunits in teleost sperm. In flounder sperm, mPRα was shown to be important in mediating sperm hypermotility as only high motility sperm with high expression of mPRα were responsive to progestin stimulation, resulting in higher fertilization success compared to low motility sperm. A single LHRHa injection resulted in increased sperm motility and fertility, associated with an increase in mPRα expression in the sperm plasma membrane. The results also suggest that the mPRα/Acy/cAMP pathway first described in croaker sperm is present in flounder sperm. Field studies of male Atlantic croaker exposed to chronic seasonal hypoxia showed that hypoxia exposure resulted in smaller gonads, lower spermatogenesis, reduced testicular mPRα expression, and in some sites, reduced sperm motility. Studies with croaker sperm using acidified activator solution to simulate ocean acidification indicated that croaker sperm were sensitive to environmental insult. Furthermore, the results suggested that the progestin signaling mechanism is more sensitive to changes in ocean pH levels than the mechanism that controls sperm motility. / text

In marine flatfish of the genus Paralichthys, temperature plays a large role in sex determination. Thus, global climate change could have significant effects on southern flounder (Paralichthys lethostigma), a commercially and recreationally important flatfish whose populations have steadily declined in Texas in the last 25 years. The most susceptible areas to global climate change are shallow water environments, particularly estuaries, which serve as essential nursery habitats for juvenile southern flounder. While in the estuaries, juveniles develop, and sex is determined. Juvenile southern flounder possess genotypic sex determination; however, the sex of females is highly influenced by temperature and can result in sex reversal. The temperature-sensitive enzyme complex responsible for estrogen biosynthesis in vertebrates is aromatase cytochrome P450 (P450arom), a critical component in ovarian differentiation that can be used to measure presumptive males and females exposed to a gradient of temperatures. This research identifies that sex is influenced by temperature between 35 and 65 mm total length (TL) and establishes that increases in temperature from 18 °C during this size range produce increasingly male skewed sex ratios in southern flounder from Texas. The findings presented here are critical for optimizing production of females in culture and for developing stock enhancement programs of southern flounder in Texas. / text

Southern flounder (Parlichthys lethostigma) is a recreationally and commercially important flatfish species found in the Gulf of Mexico, and recent analyses indicate that the northern Gulf of Mexico population is in decline. For proper management, knowledge of habitats used throughout the juvenile stage is needed. The aim of the current study is to examine habitat use of young-of-year (YOY) southern flounder in the Galveston Bay complex using habitat distribution models and acoustic telemetry. A set of habitat distribution models examined how habitat use changes during the first year of life. In addition, southern flounder were tagged with acoustic telemetry transmitters and monitored with a novel receiver array that allows for measurements of fine-scale movements. These movements were compared to habitat maps to examine habitat selection. Habitat distribution models determined that habitat requirements for southern flounder change with ontogeny and season. Newly settled southern flounder were most influenced by physicochemical parameters and the presence of seagrass beds. YOY southern flounder, however, showed increased occurrence at freshwater inlets during summer and fall months, and occurrence decreased at tidal inlets during the fall. Predictions of habitat suitability across the Galveston Bay complex indicate that the factors influencing occurrence of southern flounder change with season, ontogeny, and availability of suitable habitats. With acoustic telemetry, it was apparent that habitat use by southern flounder was nonrandom and influenced by benthic and other physicochemical conditions. Habitat analyses indicated that southern flounder used sand habitats more frequently than seagrass, oyster reef, or salt marsh habitats. Telemetry results also indicated that depth and water temperature were important determinants of habitat suitability for YOY southern flounder, with individuals preferring deeper and cooler regions of the water column in Christmas Bay. Both model and telemetry analyses indicate that habitat use by YOY southern flounder is dynamic across multiple spatial and temporal scales, with distributions and movements influenced strongly by ontogenetic changes in habitat associations, temporal and spatial variability in physicochemical conditions, and tidal cycles.