Assessment of the Health Status Atlantic Menhaden (Brevoortia tyrannus)

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Title: Assessment of the Health Status Atlantic Menhaden (Brevoortia tyrannus)
Author: Johnson, Andrea Karen
Advisors: Jay F. Levine, Committee Co-Chair
J. McHugh Law, Committee Co-Chair
Abstract: In 2002, Atlantic menhaden were collected from the White Oak, Neuse and Pamlico river estuaries in North Carolina and the seasonal changes in health indices were assessed during that period. Indicators of tissue damage (histopathological analyses of gills, heart, liver, intestine, and anterior kidney), nutritional status and exposure to environmental stressors (liver-somatic index), immune status and disease (TGF-b mRNA production, lymphocyte mitogenesis, differential counts, hematocrit, and spleno-somatic index) were compared in Atlantic menhaden from all three river systems. The bioindicators used to assess the health of Atlantic menhaden in the estuaries of North Carolina showed that there is seasonal variability in most health indices and that this pattern is strongly influenced by temperature. During the fall seasons, 2001 and 2002, Atlantic menhaden were collected from several creeks in the Pamlico River estuary. High lesion prevalence was associated with the Atlantic menhaden kills in the fall of 2001, while there were no fish kills in the fall of 2002, and lesion prevalence was very low. Indicators of tissue damage (histopathological analyses of gills, heart, liver, intestine, and anterior kidney), nutritional status and exposure to environmental stressors (liver-somatic index), immune status and disease (TGF-beta mRNA production, lymphocyte mitogenesis, hematology, plasma chemistry, and spleno-somatic index) were compared between menhaden with and without lesions over the two years. Atlantic menhaden with ulcerative lesions had significantly higher splenic mononuclear cell TGF-beta mRNA levels, spleno-somatic indices, liver-somatic indices, neutrophil and monocyte counts, and significantly lower lymphocyte counts, thrombocyte counts, hematocrit values, plasma proteins and calcium than those without. The health indicators used in this study provided information on the non-specific and specific responses of the Atlantic menhaden immune system and overall health, thus increasing our knowledge of the changes in the health of Atlantic menhaden with and without lesions. The immune-endocrine interaction was examined in captive Atlantic menhaden administered the synthetic glucocorticoid, triamcinolone acetonide. Its effects on Atlantic menhaden liver-somatic index, spleno-somatic index, hematology, plasma chemistry, lymphocyte mitogenesis, and splenic mononuclear cell TGF-beta mRNA transcription were measured and compared to untreated fish at 48 and 96 hr post-treatment. Triamcinolone-treated Atlantic menhaden showed suppression of TGF-beta mRNA production, neutrophilia, monocytosis, lymphopenia, and an increase in blood glucose levels. Knowledge of the interactions of the immune and endocrine systems provided by this study will improve our understanding of the immunodefense mechanisms of Atlantic menhaden and help us interpret some of the changes observed during the development of ulcerative lesions in wild caught Atlantic menhaden and other aquatic species. Low dissolved oxygen (DO) induced mass mortality of Atlantic menhaden (Brevoortia tyrannus) is relatively common in North Carolina estuaries. The effects of acute and subacute exposure to low DO were evaluated in Atlantic menhaden under controlled laboratory conditions. Hematology, plasma chemistry, and spleno-somatic indices were measured at five different oxygen saturations (5, 10, 15, 20, and 84%) in the acute study. Splenic TGF-beta mRNA, lymphocyte mitogenesis, and blood parameters were measured at 20% and 84% oxygen saturation in the subacute exposure study. In both experiments glucose and electrolytes were the blood parameters most affected by hypoxic conditions. Blood glucose concentrations were elevated in both studies. Fish exposed to 5% oxygen saturation in the acute study showed signs of blood acidosis while those exposed to 20% oxygen saturation in the subacute exposure study showed signs of blood alkalosis. These effects may have consequences in estuarine systems where fish are exposed to multiple stressors, which may cumulatively affect their ability to withstand additional stressful events and resist disease.
Date: 2004-11-02
Degree: PhD
Discipline: Comparative Biomedical Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/4703


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