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No description available.

No description available.

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No description available.

Variability in annual recruitment for many fishes is correlated with survival during the larval phase. Yellow perch in Lake Michigan have experienced sustained recruitment failure since 1990 and this has been blamed on low larval survival. Direct examination of factors important to larval yellow perch survival in Lake Michigan is complicated by the large size of the lake (52,000 km2) and the short length of the pelagic larval period (30-40 days). Individual-based modeling is a valuable indirect method for assessing the importance of multiple factors to larval survival. I used an individual-based modeling approach combined with field data collection to test four hypotheses regarding factors limiting survival of larval yellow perch in Lake Michigan. I tested whether larval survival is limited by prey community composition, size-selective predation, advection of larvae into offshore habitat or an interaction of these factors. I sampled larval and zooplankton abundance in Lake Michigan along a transect from 1 ? 32 km from shore in 2000 and 2001. I conducted laboratory experiments to quantify larval vulnerability to predation by three typical predators as a function of both predator and prey size. I also conducted laboratory experiments to quantify larval selectivity for different zooplankton prey as a function of larval size and prey community composition. I used the results of these experiments to develop an individual-based model specifically to describe growth and survival of larval yellow perch. Field data suggest that larval yellow perch are being transported from the nearshore to the offshore zone of Lake Michigan, but the timing of this transport varies between years. Model simulations in which the offshore prey community and the timing of larval advection were both varied suggested that larval survival will be highest in years when advection occurs within two weeks of peak hatch, allowing larvae to exploit offshore prey resources early during ontogeny. The model predicts that larvae will make foraging decisions based on prey availability as well as innate preference and they will change their diet if they are exposed to different prey communities. Model simulations also demonstrated that predation currently may not be an important factor for survival of larval yellow perch in Lake Michigan. This result is because alewife is the only fish abundant in Lake Michigan known to eat larval yellow perch. Experimental results suggest that alewife feeding rate on larval yellow perch is a positive function of larval density; yellow perch densities are currently too low to induce significant predation by alewife. Predation appears to be more important in smaller systems where larval densities are higher and larvae are exposed to other predator species. Larval survival in Lake Michigan appears to be primarily limited by an interaction of prey community composition and the timing during the larval period of offshore advection. Both factors vary between years and a good year-class is predicted when the offshore prey community is rich in cyclopoid copepods and larvae are advected offshore early. Early access to cyclopoid copepods results in an earlier transition from feeding on rotifers to feeding on copepods, which is predicted to increase larval growth and decrease mortality. These results suggest that survival of larval yellow perch in Lake Michigan is affected more by density-independent factors such as physical transport and prey community composition; Lake Michigan more closely resembles a marine environment than a typical lake with respect to larval recruitment processes. The unique aspects of larval yellow perch dynamics in Lake Michigan must be considered when applying lessons learned from analysis of larval yellow perch in other lakes to understanding survival of larval yellow perch in a large meso-oceanic system like Lake Michigan.

Terminal Schwann cells (TSCs) sit close together to form a cap over each neuromuscular junction. It is not known how TSCs interact with each other, but their close physical relationship suggests that they might form cell-cell adhesions. Adherens junctions and tight junctions are well-studied formations of cell-cell adhesions and are typically expressed near each other in the same cells. Previous research has shown that M-cadherin, one of the adherens junction proteins, colocalizes with a TSC marker, suggesting the presence of adherens junctions and tight junctions in TSCs. Additionally, claudin-19, one of the tight junction proteins, is known to be expressed by myelinating Schwann cells, but it is unknown whether claudin-19 is also expressed by TSCs. I therefore hypothesize that claudin-19 is expressed by TSCs and is involved in TSC-TSC interactions. To begin to address this hypothesis, immunolabeling against claudin-19, Schwann cells, and acetylcholine receptors was performed on both cryostat sections and whole-mount of mouse muscles. Claudin-19 expression was found at neuromuscular junctions and was localized to the axon-terminal transition, where myelin ends and TSCs begin. After denervation of the muscle and degeneration of all axons, claudin-19 expression was still present at some neuromuscular junctions. These results show for the first time the expression of claudin-19 in Schwann cells at the rodent neuromuscular junction.

A series of pond and tanks studies were conducted to determine if compensatory growth (CG) could be elicited in hybrid striped bass (HSB; Morone chrysops x M. saxitilis) through manipulations in feeding that involve sequential cycles of feed deprivation followed by daily satiation feeding. Growth, feed efficiency (FE), hepatosomatic index (HSI), intraperitoneal fat ratio (IPF), and condition factor (CF) were assessed at intervals throughout the growth trials to characterize the nutritional status (catabolic state) and CG response of HSB. Measurements of pituitary growth hormone (GH) cell activity (gene expression, protein stores), and plasma GH were assessed in tank studies to identify the potential catabolic and anabolic role of this growth promoting hormone during feed deprivation and CG. Lastly, the effects of the cyclic feeding regimes on water quality were assessed in ponds trials. In each of the three studies, growth compensation, defined by growth rates that exceed that of control fish fed daily, was observed when treatment fish were realimentated to a control daily satiation feeding following a period of feed deprivation. Cyclic feeding increased overall FE of treatment fish over the controls by 10.8-40.0 % in the first pond study (HSB fingerlings), and 7.0-8.5% in the second pond study (HSB food fish) but not in the tank study. Hepatasomatic index and CF varied significantly with feed deprivation and refeeding, and were useful predictors of the CG response following feed deprivation. There was an inverse relationship between all GH measurements and nutritional status, with no reported compensatory changes in GH. Changes in water quality parameters due to cyclic feeding were only observed in the pond study with HSB food fish. Ponds subjected to the cyclic feeding regimes had 25-38 % lower levels of total phosphorus, 23.9-41.3 % less soluble reactive phosphorus, and 11.6-27.8% less chlorophyll-a. Based on these results, CG can be repeatedly induced in HSB in both ponds and tanks, albeit full growth compensation was not achieved under the cyclic feeding conditions used in these studies. Regardless, these studies suggest that cyclic feeding can improve overall FE and water quality in pond-raised HSB. Further studies are required to ascertain the optimal catabolic conditions needed to induce full growth compensation during HSB production.

Atlantic bluefin tuna (Thunnus thynnus) occupy North Carolina waters during winter months. Their potential impact on prey populations during this time has largely been unexplored. Diet, prey-size selectivity, predator-prey size relationships, gastric evacuation rates, daily ration, and population-level predatory demand were estimated for Atlantic bluefin tuna in North Carolina during winter. Quantitative analyses of bluefin tuna stomachs collected from commercial fishers during two winters (2004-2005) were examined. Bluefin tuna diet was dominated by Atlantic menhaden with other teleosts, portunid crabs, and squid being of mostly minor importance. By weight, I found no major inter-annual differences in diet; however, intra-seasonal diet variability was evident with more diverse diets in late-fall and less diverse diets (predominantly Atlantic menhaden) during winter for one out of two years examined. Lengths of Atlantic menhaden collected from bluefin tuna stomachs were compared with lengths of Atlantic menhaden captured from the Atlantic menhaden purse seine fishery; no significant differences were observed suggesting no prey size selection. Minimum and median-sized Atlantic menhaden prey increased with increased bluefin tuna size, while maximum-sized Atlantic menhaden did not change. Diel patterns in mean gut fullness values were used to estimate the first known field derived gastric evacuation rate for this species. Daily ration from mean gut fullness values and gastric evacuation rates were used along with a range of bluefin tuna population sizes and residency to estimate population-level consumption by bluefin tuna on Atlantic menhaden. I found that, at current population levels, bluefin tuna predation on Atlantic menhaden is minimal relative to consumption of Atlantic menhaden by other known predators and commercial harvest. This was corroborated with an independent estimate of Atlantic menhaden consumption using an Ecopath model. Bluefin tuna appear to occupy coastal waters in North Carolina to prey upon Atlantic menhaden; thus, changes in the Atlantic menhaden stock status or distribution could alter winter foraging locations of bluefin tuna. This study has helped fill a gap in the knowledge of bluefin tuna natural history and provided data necessary for implementing multispecies fisheries management.