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Chapter 12. Nutrition and Fish Health

Chapter 12. Nutrition and Fish Health

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Delbert M. Gatlin III



Aquacultural production of fish and crustaceans has continued to expand throughout the world over the past decade, and additional growth is

expected in the years to come due to the increasing demand for fisheries

products and limited supplies from capture fisheries (Anonymous 1999).

In conjunction with the general increase in aquacultural production has

been a trend toward more intensification of culture practices due to scientific and technological advancements, as well as economic incentives to

increase the amount of salable product per culture unit. As a result, there

has been a tendency for marginal environmental conditions and high fish

densities, which are commonly encountered in intensive aquaculture, to

increase the likelihood of disease and other adverse health effects on cultured organisms. It also has become increasingly apparent that under the

conditions of intensive aquaculture, proper nutrition plays a critical role

in maintaining normal growth and health of aquatic organisms. All of the

essential nutrients discussed in the preceding chapters of this book should

be provided in the diet in adequate quantities to sustain the health of fish. A

number of these nutrients and other dietary components, as well as various

feeding practices, have been shown to influence the susceptibility of fish to

various infectious and noninfectious diseases. In addition, prepared diets

also may serve as a primary method of administering chemotherapeutics

and immunostimulants to fish that are infected with certain pathogenic organisms. Thus, this chapter has been structured to describe general aspects

of fish health and elaborate on the various roles that nutrition and feeding

play in sustaining the health of fish produced in aquaculture. Throughout

this chapter, the term fish is intended to include shrimp, unless otherwise


12.1.1. Conditions of Health and Disease

A primary goal but significant challenge in aquaculture is to maintain fish

in a condition of optimum health, which, in the broadest sense, means freedom from illness of any kind. A healthy condition is most conducive for rapid

growth and high survival of fish to marketable size, which are generally two

of the most important goals in aquaculture. In contrast to health, the condition of disease represents various states of illness or sickness. Disease can

be induced by a variety of factors and manifested in many different forms.

The duration and severity of disease also may vary considerably depending

on the underlying cause.

12. Nutrition and Fish Health



Factors Affecting Fish Health

The various diseases which are encountered by fish may be caused by living or nonliving agents. Living agents of disease include various infectious

organisms which may be communicable and pathogenic. Organisms known

to cause disease in fish include bacteria, fungi, viruses, and various kinds

of parasites. Nonliving agents that adversely affect fish health may originate

from inside or outside the fish. External factors such as environmental conditions may alter normal physiological processes and cause disease. Likewise,

endogenous factors such as the genetic constitution of a fish may influence

its susceptibility to less than optimal environmental conditions or infectious

agents. It is well established that various fish species, and certain strains

within a given species, may exhibit widely different tolerances to various environmental conditions and infectious agents (Plumb 1994; Wiegertjes et al.


12.2.1. Environmental Conditions

There is a variety of environmental conditions which, if allowed to exceed

certain limits, can impair normal physiological processes of fish and thus

compromise their health. An inverse relationship between environmental

quality and fish disease is well established in aquaculture (Plumb 1994). The

water in which a fish lives is the principal environmental component that

influences its health. Some of the most critical water quality conditions that

are readily influenced by biological activity, and thus of primary concern

in intensive aquaculture, include dissolved oxygen, un-ionized ammonia,

nitrite, carbon dioxide, and pH. Maximum and minimum tolerable and

lethal concentrations for many of these metabolites and constituents have

been established for numerous fish species (Stickney 1994). Other water

quality characteristics which are not influenced by biological activity such

as alkalinity, hardness, salinity, temperature, and turbidity also may affect

the health of fish, especially if they are not within normal tolerable limits.

Different fish species may vary considerably in terms of specific tolerance

limits for various water quality characteristics (Evans 1993). In addition to

these natural components which comprise water quality, there is a variety of

natural and synthetic chemicals which may contaminate water and adversely

affect the health of fish.

A primary task in aquaculture is to maintain water quality conditions

within tolerable levels for the species being cultured, but this is not always

achieved. Even if lethal concentrations of certain metabolites or other water

quality variables are avoided, fish health can be compromised by stress that


Delbert M. Gatlin III

may be imposed if fish are required to tolerate less than optimum water

quality conditions (Roberts 2000). Thus, the adverse water quality could be

viewed as a stressor and the resulting stress would be a physiological state

or condition in which normal functioning is impaired. Stress also may be

imposed by other conditions in aquaculture such as crowding, antagonistic

interactions among fish, and handling such as harvesting, sorting, or grading. Inadequate nutrition in the form of nutrient deficiencies, improper

feeding regimes, or the presence of toxins in the diet also may impose stress

on fish. All forms of stress caused by various environmental offenses tend to

reduce the health of fish and make them more susceptible to various kinds

of pathogenic organisms. This is generally believed to result from physiological changes that suppress the fish’s natural resistance and immunity.

12.2.2. Infectious Agents

Infectious diseases are a major cause of economic loss in commercial

aquaculture. There are various disease-causing organisms that may infect

fish including bacterial, fungal, parasitic, and viral pathogens (Noga 1996).

The biology of these various pathogens, including their environmental requirements, host specificity, virulence, and methods of control, has been

reviewed extensively in several publications (Stoskopf 1992; Plumb 1994;

Stickney 1994; Noga 1996).

Some disease-causing organisms are obligate pathogens in that they must

have a host or intermediate host to survive. In contrast, facultative pathogens

are able to live and multiply in a host or in the environment without a

host being present. Infection by a pathogenic organism can occur without

a diseased condition being produced. But when conditions are favorable,

infection by a pathogenic organism will result in disease. Infectious diseases

are most commonly manifested in aquaculture when fish become stressed

due to less than optimal environmental conditions. Thus, it is of utmost

importance to avoid conditions that induce stress in fish to maximize their

resistance to various disease-causing organisms.

12.2.3. Immunity and Disease Resistance

Fish have a reasonably well-developed immune system consisting of both

nonspecific and specific components (Iwama and Nakanishi 1996). The

nonspecific component is considered natural or innate immunity and consists principally of phagocytic mechanisms associated with macrophages and

granular leukocytes such as neutrophils which are designed to attack microorganisms that invade the fish’s skin or mucous. In addition to phagocytes, there are other soluble factors such as lysozyme and complement

which may assist in destroying invading pathogens.

12. Nutrition and Fish Health


The specific component of the immune system consists of humoral and

cell-mediated responses which may provide specific immunological memory,

although this immune memory of fish is generally considered to be less developed than that of mammalian species. The rate of induction and the level

of response are readily influenced by temperature. In the specific immune

response, macrophages serve as antigen-presenting cells, while B lymphocytes are involved in antibody production. In addition, T lymphocytes are

involved in cell-mediated immunity by stimulating the differentiation and

proliferation of B lymphocytes. Once antibodies are produced to a specific

pathogen, they bind to the pathogen’s membrane so that it can be destroyed

via activation of the complement system through its classical pathway.

There has been a growing body of evidence in recent years which indicates

that various immune responses (Fig. 12.1) and disease resistance of fish

can be influenced by both nutrients and nonnutritive components of the

diet. Enhancement of the immune responses of fish and their associated

resistance to disease through dietary means has been viewed as an attractive

alternative to treating fish, given the very limited number of efficacious and

approved chemicals which are available for use after they become diseased.


Dietary Components Influencing Fish Health

Proper nutrition has long been recognized as a critical factor in promoting normal growth and sustaining health of fish. Artificial diets manufactured from various feedstuffs are the primary source of nutrition in

intensive aquaculture. Prepared diets not only provide the essential nutrients that are required for normal physiological functioning but also may

serve as the medium by which fish are exposed to other components which

may affect their health either positively or negatively.

12.3.1. Nutrients

Previous chapters in this book have described in detail the various nutrients and their specific functions, dietary requirements, and signs of deficiency in fish. It is well established that all essential nutrients are required

in adequate quantity to sustain normal health. A deficiency of any nutrient,

if severe enough, can adversely affect fish health either directly, by impairing metabolic functions, or indirectly, by making fish more susceptible to

opportunistic disease-causing agents. Thus, artificial diets used in aquaculture are typically formulated to provide adequate quantities of all nutrients

to prevent deficiency. However, dietary supplementation of certain nutrients at levels above those which satisfy minimum requirements has allowed

12. Nutrition and Fish Health


enhancement of some immune responses and disease resistance of numerous terrestrial animals (Reddy and Frey 1990) as well as several fish species

(Landolt 1989; Lall and Olivier 1991). This section considers the various nutrients groups with regard to their ability to enhance the immunity, disease

resistance, and health of fish. Many of the published studies concerning immune responses of fish fed certain nutrients above minimum requirement

levels are summarized in Table 12.1. Energy-Yielding Nutrients Protein and Amino Acids. The minimum dietary requirement

for protein or a balanced mixture of amino acids is of primary concern in

aquaculture because satisfying this requirement is necessary to ensure adequate growth and health of fish, while providing excessive levels is generally

uneconomical, as protein is the most expensive dietary component. As such,

most studies have been concerned with determining minimum dietary protein requirements for maximum weight gain and accretion of body protein.

Dietary requirements of fish for the 10 indispensable amino acids also have

received considerable attention. However, there have been limited investigations concerning manipulation of dietary protein and amino acids to

enhance fish health even though immunoglobulins and other components

of the immune system are proteinaceous. In one study (Kiron et al. 1995a),

rainbow trout (Oncorhynchus mykiss) fed a diet containing only 10% protein

had reduced lysozyme activity and C-reactive protein in serum compared

to fish fed diets with 35 and 50% protein, but antibody production was not

affected by dietary protein level. Mortality associated with a controlled exposure to Aeromonas salmonicida also was elevated in fish fed the diets with

10 and 50% protein compared to those fed the diet with 35% protein. Reduced parasitism was observed in rainbow trout fed a protein-deficient diet

(19% crude protein) compared to a control diet with 38% protein (Thomas

and Woo 1990). More research concerning the effects of dietary protein on

immune responses of fish is certainly warranted.

Arginine is one amino acid whose influence on health has received

considerable attention with experimental animals (e.g., Saito et al. 1987;

Madden et al. 1988) and recently, to a more limited extent, with fish (Neumann et al. 1995; Buentello and Gatlin 1999). This amino acid is

FIG. 12.1

Several nutrients and nonnutritive diet additives have been documented as

influencing various components of the fish immune system including (A) specific

immunity via antibody production, (B) macrophage killing ability via oxidative

reactions, and (C) functioning of the complement system. (Adapted from V. Verlhac

and J. Gabaudan, “The Effects of Vitamin C on Fish Health,” Centre for Research in

Animal Nutrition, Societe Chimique, Paris, France, 1997, with permission.)

Table 12.1

Immune Responses and Disease Resistance of Fish Fed Selected Nutrients at Dietary Concentrations Above Those Required for Normal Growth


Vitamin Cb


Channel catfish


Rainbow trout

Dietary concentration


Duration of


150 AA

3,000 AA

14 weeks

20 weeks

4,000 AA

13 weeks

9 weeks

1,000 APP

7 weeks

>2,000 APP

250 APP

8 weeks

10 weeks

2,000 AA

12 weeks

2,000 AMP and SCAA

8 weeks

4,000 APP

2 weeks

Immune responsea

+ Edwardsiella tarda

+ Complement hemolytic


+ Antibody

+ E. ictaluri

− Complement hemolytic


− Antibody

+ E. ictaluri

− Neutrophil bactericidal


− Phagocytosis

− E. ictaluri

− Antibody

− E. ictaluri

+ Antibody

+ Vibrio anguillarum

+ Ichthyophthirius multifilis

− Specific immunity

+ Complement (alternative)

+ Chemiluminescence

+ Macrophage

− Lysozyme

− Antibody

− Complement (classical)


Durve and Lovell (1982)

Li and Lovell (1985)

Liu et al. (1989)

Johnson and

Ainsworth (1991)

Li et al. (1993)

Li et al. (1998)

Navarre and

Halver (1989)

Wahli et al. (1995)

Verlhac et al. (1996)

Atlantic salmon

1,000 APP

2 weeks

2,750 AA

26 weeks

5,000 AA and AS

2,980 AA and 4,770 AS

72 days


4,000 AMP

24 weeks

1,000 APP

3,170 AA

23 weeks

+ Chemiluminescence

+ Pinacytosis

+ Lysozyme

+ Complement (classical)

+ Antibody

− Complement (alternative)

− Lymphocyte proliferation

+ Complement

+ A. salmonicida

+ Lymphokine

− Antibody

− Phagocytosis

− Respiratory burst

− Antibody

+ Antibody

− Yersinia ruckeri

− Vibrio salmonicida

+ Complement

+ Lysozyme

+ A. salmonicida

+ Antibody

+ Hydrogen peroxide

+ Lymphocyte proliferation

− Respiratory burst

− Bactericidal activity

+ A. salmonicida killing

− Leukocyte migration

− − Antibody

Verlhac et al. (1998)

Hardie et al. (1991)

Sandnes et al. (1990)

Erdal et al. (1991)

Waagbo et al. (1993)

Verlhac and

Gabaudan (1994)

Thompson et al. (1993)


Table 12.1 (Continued)


Vitamin E


Duration of


Red sea bream

1,000 AA

6 weeks


2,000 CA

127 days

Sockeye salmon

10,000 AS

231 days

Channel catfish


120 days


180 days

Rainbow trout


22 weeks

Atlantic salmon


20 weeks


Atlantic salmon


12 weeks


Vitamin A

Dietary concentration


Rainbow trout


9,000 IU/kg

16 weeks

Immune responsea

− Complement

+ Hemagglutinin titer

+ Phagocytic index

+ Lysozyme

− R. salmoninarum

− Antibody

+ Macrophage intracellular

superoxide anion

+ Phagocytic index

− Antibody

+ Y. ruckeri

− Antibody

− Leukocyte count

− Serum protein

− Lysozyme

+ Phagocytosis

− Respiratory burst

− Lymphokine production

+ Phagocytosis

+ Antiprotease

+ Migration

+ A. salmonicida

− IgM

− Lysozyme

− Respiratory burst


Yano et al. (1988)

Roberts et al. (1995)

Bell et al. (1984)

Wise et al. (1993a)

Wise et al. (1993b)

Furones et al. (1992)

Hardie et al. (1990)

Pulsford et al. (1995)

Thompson et al. (1994)

Thompson et al. (1995)


Channel catfish


10 weeks


Atlantic salmon


28 weeks


Channel catfish


8 weeks

Atlantic salmon


20 weeks



Channel catfish


Channel catfish


9 weeks

(Selenomethionine and selenoyeast)

(Had a higher potency than Na2 SeO3 )


10 weeks


10 weeks

(Zinc methionine had a higher

potency than zinc sulfate)


16 weeks

+ E. ictaluri

+ Antibody

− Antibody

− Lysozyme

− Complement hemolytic


+ Spontaneous hemolytic


− Antibody

− Chemiluminescence

− Macrophage migration

− E. ictaluri

− Total antibody

− Specific hemolytic


− Spontaneous hemolytic


− Lysozyme

+ E. ictaluri

+ Antibody

+ Macrophage chemotaxis

− Aeromonas hydrophila

+ E. ictaluri

+ Antibody

Eya and Lovell (1998)

+ Neutrophils

+ Chemotaxis

− Phagocytosis of E. ictaluri

− E. ictaluri

Lim et al. (1996)

El-Mowafi et al. (1997)

Sealey et al. (1997)

Andersen et al. (1998)

Wang et al. (1997)

Scarpa and Gatlin (1992)

Paripatananont and

Lovell (1995)

+, increase; −, no change; and − −, decrease.

Provided as ascorbic acid equivalents by either crystalline l-ascorbic acid (AA), ascorbate-2-monophosphate (AMP), ascorbate-2-polyphosphate

(APP), silicone-coated AA (SCAA), calcium ascorbate (CA), or ascorbate sulfate (AS).




Delbert M. Gatlin III

involved in the synthesis of nitric oxide via nitric oxide synthase, which is inducible in fish (Schoor and Plumb 1994; Neumann et al. 1995). Nitric oxide

has many physiological functions including enhancement of macrophage

cytotoxicity. Arginine has been shown to have numerous beneficial effects on

T cell-mediated immunity in various animal models and in humans (Madden

et al. 1988). Thus its involvement in fish health is certainly worthy of further

investigation. Carbohydrate. Due to the fact that fish do not have a specific

dietary requirement for carbohydrate, its inclusion in diets is to provide a

relatively inexpensive source of energy. However, the ability of fish to utilize dietary carbohydrate for energy varies considerably (NRC 1993; Wilson

1994), and excessive soluble carbohydrate (principally starch) in the diet of

some carnivorous fish has been associated with impaired health, due principally to glycogen accumulation in the liver (e.g., Hilton and Hodson 1983).

In one study with Atlantic salmon, digestible carbohydrate at from 0 to 30%

of the diet had minor effects on humoral immune responses after vaccination with Vibrio salmonicida, although cumulative mortality after exposure to

this organism was lowest in fish fed 10% carbohydrate (Waagbo et al. 1994).

Oligosaccharides in feedstuffs such as soybean meal have been shown to

affect adversely the health of Atlantic salmon due to intestinal disturbance

(e.g., van der Ingh et al. 1996) but other species appear to be more tolerant

of these compounds.

In contrast to the soluble and fibrous carbohydrates associated with common feed ingredients included in fish diets, some structural carbohydrates

associated with the cell walls of yeast and fungi such as β-glucans and mannan oligosaccharides have been shown to enhance the immune response of

some fish species. These compounds are considered further in the section

concerning nonnutritive dietary components. Lipids and Essential Fatty Acids. Lipids are important components of fish diets because they provide a concentrated source of energy

that is typically well utilized. In addition, dietary lipids supply essential fatty

acids which cannot be synthesized by the fish. Adequate quantities of these

essential fatty acids must be provided in the diet to sustain normal growth

and health of fish, but excessive levels have been shown to have growthsuppressing effects (NRC 1993). Another potentially negative health effect

associated with dietary lipid can be attributed to rancidity of the lipid. Many

fish diets contain relatively high levels of polyunsaturated fatty acids, which

are particularly susceptible to oxidation. Various products of lipid oxidation

may react with proteins, vitamins, and other dietary components to limit

their nutritional value. Vitamin E is particularly susceptible to destruction by

oxidized lipid due to its antioxidant properties. Thus, feeding oxidized lipid

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Chapter 12. Nutrition and Fish Health

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