Artificial chemical marking of calcified structures, such as otoliths, has emerged as a powerful method to assess stocking success and determine connectivity patterns in freshwater and marine systems. Although transgenerational and larval immersion methods have been validated, dietary transmission of enriched stable isotopes to calcified structures would allow minimal handling of animals and reduced expense for flow-through systems. We experimentally manipulated 137Ba in diets and successfully marked otoliths in red drum (Sciaenops ocellatus) larvae, fingerlings, and subadults, as well as fin rays and scales of subadults in as little as 2 weeks of exposure. Marking success of 100% was found for larvae and fingerlings reared at higher temperatures, indicating the need for sufficient growth to occur for consistently detectable marks. Spiked isotopes successfully marked fin rays (86% marked) and scales (100% marked) of subadults, providing a cost-effective tagging method that can be sampled nonlethally. Dietary marking of calcified structures may be the method of choice where handling must be minimized or water chemistry cannot be manipulated.
Per-
and polyfluoroalkyl substances (PFASs) have attracted scientific
and regulatory attention due to their persistence, bioaccumulative
potential, toxicity, and global distribution. We determined the accumulation
and trophic transfer of 14 PFASs (5 short-chain and 9 long-chain)
within the food web of the Yadkin-Pee Dee River of North Carolina
and South Carolina, US. Food web components and pathways were determined
by stable isotope analyses of producers, consumers, and organic matter.
Analyses of water, sediment, organic matter, and aquatic biota revealed
that PFASs were prevalent in all food web compartments. Biofilm, an
aggregation of bacteria, fungi, algae, and protozoans and a basal
resource for the aquatic food web, showed high PFAS accumulation (in
10 of 14 compounds), particularly for perfluorooctanoic acid, with
the greatest mean concentration of 463.73 ng/g. The food web compartment
with the most detections and greatest concentrations of PFASs was
aquatic insects; all 14 PFASs were detected in individual aquatic
insect samples (range of
Persistent and bioaccumulative contaminants often reach concentrations that threaten aquatic life by causing alterations in organism behavior and development, disruption of biological processes, reproductive abnormalities, and mortality. The objectives of this research were to determine the aquatic food web structure and trophic transfer and accumulation of contaminants within a riverine ecosystem and identify potential stressors to the health of an imperiled fish, the robust redhorse (Moxostoma robustum) and other species of conservation concern in a large Atlantic Slope (USA) river. Trophic position was determined for food web taxa by stable isotope analyses of representative producers, consumers, and organic matter of the Yadkin-Pee Dee River of North Carolina and South Carolina. Contaminant analyses were performed on water, sediment, organic matter, and aquatic biota to assess the prevalence and accumulation of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), current use pesticides (CUPs), polycyclic aromatic hydrocarbons (PAHs), and selected metals. Contaminants were prevalent in the environment and food web components of the river. PCBs were detected in 32% of biotic samples (mean 0.24μg/g dry weight [DW], range 0.01-3.33μg/g DW), and DDTs (legacy OCPs and metabolites) were detected in 90% (mean 0.014μg/g DW, range 0.0004-0.29μg/g DW). The trace metals manganese and cadmium exceeded published threshold effect concentrations in sediment (460 and 0.99μg/g DW, respectively). Mercury was detected in all food web samples exhibiting a mean of 0.61μg/g DW and range 0.006-2.35μg/g DW (mean 0.13μg/g wet weight [WW], range 0.001-0.6μg/g WW). Concentrations exceeded the 0.2μg/g WW aquatic life criterion for mercury in 38% of fish samples. Fish trophic magnification factors (TMFs; range 0.33-3.75) indicated that contaminant accumulation occurred from both water and dietary sources. The combination of analytical approaches applied here provides new insight into contaminant dynamics with conservation implications.
Physiological information is rarely used in descriptions of maturity for managed, wild fish species; however, the use of physiological data holds great promise to provide important detail on the complexities of oocyte development and maturity. Investigating southern flounder ()-an overfished commercial and recreational fishery resource-we examined pre-spawn physiological changes in females to provide further detail of the maturation process. Given that adults of this species complete maturation and spawn in unknown offshore locations, information on pre-spawn physiological changes is particularly informative for both size- and age-based patterns of maturity. We evaluated seasonal and ontogenetic changes in hormone concentrations in blood plasma that are commonly associated with sexual maturation, in addition to quantifying and classifying lipid stored in liver tissue. We found a strong positive relationship between body weight and lipid content during all months, as well as evidence for mobilization of lipids among larger females in September and October, presumably for gonadal development. Throughout the sampling period, the lipid content of smaller individuals was dominated by structural lipids (as opposed to storage lipids). In contrast, larger individuals possessed greater amounts of storage lipids. This suggests that larger, putatively maturing individuals were accumulating storage lipids for later production of vitellogenin. Females sampled for blood sex steroids and ovarian histology showed different testosterone and estradiol concentrations between putatively maturing and immature fish, and temporal variation with peaks in October and November. Overall, emerging patterns of liver lipid content and composition and blood steroid concentrations describe a multi-month maturation process that is often managed one dimensionally over short time periods. Insights from this work will improve our understanding of the life history of southern flounder, with the potential for better understanding of the dynamics of offshore spawning migration and informing subsequent species management.
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