Dietary Nutrients, Additives and Fish Health

Cheng-Sheng Lee

• Publisher: Wiley-Blackwell
• Year: 2015
• ISBN:
  9781119005537
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Fisheries & Aquaculture
• Index: Technology & Engineering

Fish nutrition can be the deciding factor between a robust and healthy farmed fish population and low aquaculture production. In an age where chemicals and antibiotics are under greater scrutiny than ever, a strong understanding of the role of nutrients and feed additives is essential in the aquaculture industry.

Dietary Nutrients, Additives and Fish Health is a comprehensive review of dietary nutrients, antinutritional factors and toxins, and non-nutrient dietary additives, and their effects on fish performance and immune system function, as well as overall health.

The book opens with an overview of fish immune systems and health. Subsequent chapters delve into proteins and amino acids, lipids and fatty acids, carbohydrates, beta glucans, vitamins, minerals, antinutrients, mycotoxins, nucleotides, prebiotics, probiotics, organic acids and their salts, and plant extracts and their impacts on fish health, growth, and development. The text then concludes with a chapter on feeding practices.

Authored by leaders in aquaculture, Dietary Nutrients, Additives and Fish Health will be an invaluable resource to graduate students, researchers and professionals alike.

Chapter 1

Overview of Fish Immune System and Infectious Diseases

Craig Shoemaker¹, De-Hai Xu¹, Benjamin LaFrentz¹, and Scott LaPatra²

¹United States Department of Agriculture, Agricultural Research Service, Aquatic Animal Health Research Unit, Auburn, AL, USA

²Clear Springs Foods Inc., Research Division, Buhl, ID, USA

Introduction

Cultured finfish are an important source of animal protein worldwide (Naylor et al. 2009), and the Food and Agriculture Organization (FAO) reported that over half of the world’s supply of fish and shellfish is now from aquaculture (FAO 2008). As fish consumption increases and natural fish stocks decrease, aquaculture practices will need to intensify in order to meet global demand. Intensification will likely lead to an increase in disease problems, due to a higher number of animals in a limited and confined environment and the influence of poor environmental conditions (i.e., water quality) on the fish immune system. For example, limited disease-related problems were reported in the channel catfish (Ictalurus punctatus) industry prior to 1980 because stocking densities were less than 10,000 fish/ha and maximum feeding allowances were about 50 kg/ha/day with most farms using a single crop system (Hawke and Khoo 2004). Production intensity increased following that time with >12,000 fish/ha stocked, and feeding increased accordingly to 90–112 kg/ha/day. Multi-cropping systems (i.e., various sizes of fish cultured together) that utilized limited water exchange were also employed (Hawke and Khoo 2004). As a result, up to 45% of on-farm losses were reported to be due to infectious disease (USDA/APHIS 1997). The emergence or re-emergence of pathogens will likely be seen in many aquaculture ventures as production intensifies and degrades environmental parameters.

Immunity is the inherited ability to recognize and respond defensively against foreign living and non-living agents. The immune response is a coordinated response of immune cells and molecules and memory in vertebrate animals (including fish) that occurs as a result of recognition of foreign agents. Fish have evolved with both non-specific (innate immunity) and adaptive (acquired) immune mechanisms. The innate immune response is limited in specificity via germline encoded pathogen recognition receptors (PRRs) that respond to pathogen-associated molecular patterns (PAMPs) such as bacterial or fungal glycoproteins and lipopolysaccharides (Kawai and Akira 2010; Boltana et al. 2011). The innate response is an important first line of defense, especially in larval fish. Research suggests that the innate immune response is important in priming and regulating adaptive immunity (Fearon and Locksley 1996). Adaptive immunity allows for specificity and memory (Pilström 2005; Secombes et al. 2005). This chapter provides an overview of the fish immune system and the infectious diseases of fish (bacterial, viral, parasitic, and fungal).

Immune Organs and Tissues

Thymus

The thymus of fish is composed of lymphoblasts (early immune cells) in a reticular endothelial cell network; it is the first organ to obtain mature lymphocytes during immune maturation (Manning 1994; Rombout et al. 2005). Evidence in fish supports the notion that the thymus is responsible for the development of T-lymphocytes (T-cells), as is the case in other jawed vertebrates. T-cell selection occurs in the thymus, and only T-cells that recognize foreign antigenic peptides in the context of self major histocompatibility complex (MHC) molecules are released (Kuby 1994). T-cells that recognize self antigen and self MHC are killed via programmed cell death or apoptosis. Mature T-cells are then released from the thymus and become distributed in the immunological organs and tissues (Rombout et al. 2005). In adult fish, as in mammals, the thymus decreases significantly in size.

Kidney

The kidney is important in hematopoiesis and contains two segments: the anterior or head kidney and the posterior or trunk kidney. Blood cell differentiation occurs here instead of in bone marrow, as in mammals. Early in development, the entire kidney is involved in production of blood cells and early immune responses. The anterior kidney is considered the primary B-lymphocyte (B-cell) organ and is where the B-cells develop. As the fish matures, the posterior kidney is primarily involved in filtration and/or urinary functions. The kidney also contains the reticuloendothelial system, which is a network of sinusoids lined with phagocytic cells that have roles in antigen presentation. There is usually a concentration of melanomacrophage centers consisting of macrophages, lymphocytes, and plasma cells, and these centers are involved in antigen trapping and immune responses (Agius and Roberts 2003).

Spleen

The spleen is a secondary immune organ in fish and is involved in antigen processing, antibody production, and memory. Most fish spleens are not organized into red and white pulp, as in mammals. Manning (1994) demonstrated in carp (Cyprinus carpio) that the proliferative response to antigen was scattered and not organized into thymus-dependent and -independent regions. Melanomacrophage centers are also located in the spleen and are primarily responsible for the breakdown of erythrocytes. However, as discussed above, they may be involved in antigen presentation and immunologic memory. In rainbow trout (Oncorhynchus mykiss), Hadidi et al. (2008) demonstrated that the spleen size predicted the resistance to Flavobacterium psychrophilum, suggesting a role in innate immunity.

Gut

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