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The Gulf killifish Fundulus grandis is a euryhaline baitfish species with commercial aquaculture potential. The low salinity and freshwater tolerance of early life-stages of F. grandis were evaluated to determine the potential for inland culture and guide production protocols. Egg fertilization and embryo survival decreased in fresh water, but freshwater incubation improved larval freshwater tolerance. In juveniles, survival and growth were reduced in fresh water from 2-6 weeks post-hatch but not from 7-11 or 12-16 weeks post-hatch. Na+/K+-ATPase activity and whole body Na+ content were elevated in low salinity treatments of the 7-11 weeks post-hatch age group, indicating substantial osmoregulatory ability at that age. RNA expression data from this age group indicated that freshwater acclimation is accompanied by an initial up-regulation of carbonic anhydrase followed by prolonged up-regulation of Na+/K+-ATPase. By 12-16 weeks post-hatch, F. grandis osmoregulatory ability is well developed with minimal differences among osmoregulatory data.

Title from PDF of title page. / Document formatted into pages; contains 71 pages. / Thesis (M.S.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Thalassia testudinum, a stenohaline seagrass species, and Ruppia maritima, a euryhaline submerged aquatic vegetation species, were subjected to the same seven salinity levels (0 - 60) in a controlled environment. The response variables examined were the occurrence of leaf discoloration, plant growth rates, photosynthetic characteristics of blade segments (Pmax, respiration, alpha, and Ik), and osmolality changes within the plant tissues. These response variables were measured at exposure times of one, seven, and 28 days. Greater than 75% leaf discoloration occurred in Thalassia testudinum blades placed in 0, and 60 psu, while Ruppia maritima blades only became severely discolored in 60 psu. Plant growth rates were highest in 40 psu for T. testudinum and 20 psu for R. maritima. Pmax for both species was somewhat affected by salinity changes, but the plants did not appear to be photosynthetically compromised in their "optimal" ranges over time. / ABSTRACT: Salinity effects on photosynthesis were less pronounced in R. maritima than in T. testudinum, which would be expected when comparing a euryhaline species to a stenohaline species. Both intercellular and intracellular osmolality showed a pattern of increase or decrease as the treatment salinities were altered from ambient levels (30 psu for T. testudinum and 20 psu for R. maritima). After one day of exposure to a new treatment salinity, the intercellular osmolality had changed significantly from ambient value, with a second shift, occurring mostly in the salinity extremes, for both seagrass species. This second shift is most likely due to the fact that at the extremes, the plants are being compromised. Changes in these physical and physiological responses indicate that significant increases and decreases in ambient salinity levels are initially stressful for both species. / ABSTRACT: Both seagrass species had an optimal salinity as well as a range of salinities in which the long-term physiological stresses did not cause tissue death. Thalassia testudinum had the fewest stress responses in 40 psu, with an optimal range of 20 - 40 psu. Ruppia maritima had the fewest stress responses in 20 psu (growth salinity) with an optimal range of 0 - 40 psu. In this study, neither species was able to survive for 28 days in 60 psu (at which point the plants had been out of their respective optimal salinities for at least 42 days). / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Thalassia testudinum, a stenohaline seagrass species, and Ruppia maritima, a euryhaline submerged aquatic vegetation species, were subjected to the same seven salinity levels (0 - 60) in a controlled environment. The response variables examined were the occurrence of leaf discoloration, plant growth rates, photosynthetic characteristics of blade segments (Pmax, respiration, alpha, and Ik), and osmolality changes within the plant tissues. These response variables were measured at exposure times of one, seven, and 28 days. Greater than 75% leaf discoloration occurred in Thalassia testudinum blades placed in 0, and 60 psu, while Ruppia maritima blades only became severely discolored in 60 psu. Plant growth rates were highest in 40 psu for T. testudinum and 20 psu for R. maritima. Pmax for both species was somewhat affected by salinity changes, but the plants did not appear to be photosynthetically compromised in their "optimal" ranges over time. Salinity effects on photosynthesis were less pronounced in R. maritima than in T. testudinum, which would be expected when comparing a euryhaline species to a stenohaline species. Both intercellular and intracellular osmolality showed a pattern of increase or decrease as the treatment salinities were altered from ambient levels (30 psu for T. testudinum and 20 psu for R. maritima). After one day of exposure to a new treatment salinity, the intercellular osmolality had changed significantly from ambient value, with a second shift, occurring mostly in the salinity extremes, for both seagrass species. This second shift is most likely due to the fact that at the extremes, the plants are being compromised. Changes in these physical and physiological responses indicate that significant increases and decreases in ambient salinity levels are initially stressful for both species. Both seagrass species had an optimal salinity as well as a range of salinities in which the long-term physiological stresses did not cause tissue death. Thalassia testudinum had the fewest stress responses in 40 psu, with an optimal range of 20 - 40 psu. Ruppia maritima had the fewest stress responses in 20 psu (growth salinity) with an optimal range of 0 - 40 psu. In this study, neither species was able to survive for 28 days in 60 psu (at which point the plants had been out of their respective optimal salinities for at least 42 days).

Osmoregulation is an essential process to maintain water and ionic balance and when euryhaline fish move between freshwater and seawater environments as part of their life cycle this presents additional osmoregulatory challenges. Migrating fish can be exposed in both environments to pollutants such as endocrine disrupting chemicals (EDCs) that include natural hormones (e.g. 17β-estradiol; E2), synthetic hormones (e.g. 17α-ethinylestradiol; EE2), and industrial chemicals (e.g. nonylphenol). The focus of this thesis was to study the effects of different categories of EDCs on the osmoregulatory functions of euryhaline fish such as three-spined sticklebacks (Gasterosteus aculeatus) and rainbow trout (Oncorhynchus mykiss). Osmoregulatory variables (such as osmolality, water and ionic content) were compared in plasma and tissues (white muscle and carcass) of rainbow trout. This validated the use of specific tissue parameters as a surrogate of plasma responses to various osmoregulatory challenges. Waterborne exposure to 17α-ethinylestradiol revealed differential sensitivity of vitellogenesis in the three-spined sticklebacks (no induction) and rainbow trout, but had a significant effect on calcium homeostasis in both species. Intraperitoneal implants of 17β-estradiol reduced CaCO3 production and apparent water absorption in the intestine and increased in tissue calcium stores of seawater-acclimated trout, but fish were able to compensate and showed no overall osmoregulatory disturbance. Waterborne exposure to nonylphenol in freshwater trout was also investigated, but no effects on osmoregulation were found up to 2 ng/l. Overall, estrogens can affect osmoregulation differentially in euryhaline fish species, and sometimes at EDC levels lower than the threshold for reproductive effects (i.e. vitellogenin induction).