Aquacultured products assist the human demands for seafood so that foodfish supplies can remain sustainable and consistent. Although the fish-farming industry has seen dramatic growth and intensification in recent years, the latter has led to an increase in bacterial diseases and fish health management problems, resulting in major economic losses around the world. In addition to the lack of understanding of fish physiology, these complications are exacerbated by the inappropriate and controversial use of antibiotics. This work addressed these issues in striped catfish (Pangasius hypophthalmus) and Nile tilapia (Oreochromis niloticus), two economically important foodfish, by investigating alternative, more cost-effective options to promote fish health. The first two studies established reference intervals for immunology, hematology and plasma chemistry analytes in striped catfish in a recirculating aquaculture system (RAS). In a third study, the immunomodulatory effects after directly feeding probiotic strains of Bacillus subtilis NZ86 and O14VRQ in Nile tilapia were ascertained. This last study revealed that supplementation with both of the probiotic strains for 51 days stimulated several local and systemic innate immune responses of tilapia. When these transient probiotic bacteria were present in the gut, a pro-inflammatory environment was developed as evidenced by the localized higher expression of the cytokines tumor necrosis factor (TNF) – α and interleukin (IL) – 1β. Significant increases (p < 0.05) were noted differentially by both probiotic strains throughout the trial in plasma lysozyme content, alternative complement activity, and in the peripheral blood leukocyte profiles. Additionally, there were trends for increased levels of phagocytosis and respiratory burst in leukocytes of the anterior kidney and spleen at the end of the trial, suggesting the potential use of these probiotic strains for improved immune-competence. These findings help to understand and clarify the potential mechanism of action associated with the increased disease resistance recorded in preliminary studies with the same probiotic strains. Implementation of the tools established and validated in this work could be useful in evaluating fish welfare situations involving striped catfish grown in RAS conditions, and also show promise for a healthier foodfish supply where antibiotic applications practices could be minimized. / Ph. D. / Aquaculture, or fish farming, is one of the most prosperous production sectors of animal-derived food. Despite the success story of aquaculture, the fish industry is heavily plagued by bacterial diseases, which cause losses in billions of dollars annually around the world, and directly contribute to increases in human food insecurity. Since the options to cost-effectively address diseases are limited, I explored alternative ways to more safely monitor and also ensure optimal health in striped catfish and tilapia, two globally important aquaculture fishes. I investigated the values of different cellular and chemical components of the blood to monitor the health of striped catfish when grown in indoor recirculating conditions, in order to understand normal catfish physiology. The values of these blood components were comparable to those of other freshwater fishes. As part of another study, I supplemented probiotics in the diet of the tilapia for 51 days, and assessed the effects of these on the immune system of the fish. Dietary supplementation of the probiotics resulted in the presence of the probiotics in the gut of the fish. Furthermore, the presence of these microbes was tightly linked to elevated values of numerous functions of the immune system. These functions included levels of lysozyme, alternative complement, and percentage of neutrophils, which are all related with a state of heightened immunity in the animal host. The tools that I established and validated in this study are promising alternatives to optimize the health of these two important foodfish. Moreover, they could be useful for the fish farmer because of their greater cost-effectiveness, and can potentially lead to a safer foodfish supply by decreasing the reliance on antibiotics.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/91933 |
| Date | 29 January 2018 |
| Creators | Galagarza, Oscar Andres |
| Contributors | Food Science and Technology, Kuhn, David D., Williams, Robert C., Eifert, Joseph D., Smith, Stephen A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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