|
|
|
|
|
|
|
Table 1 lists vitamin C requirements for various species. An interaction between vitamin A and vitamin C has been shown, with higher dietary levels of vitamin A (88 IU versus 7 IU per g diet) increasing the severity of vitamin C deficiency signs in rainbow trout (Primbs et al, 1971). Fish are protected from vitamin E deficiency in a dose-dependent manner by vitamin C (Hamre et al., 1997).
|
 |
|
|
|
|
|
|
|
The ascorbic acid and magnesium requirements of carp may be elevated by an increase in dietary protein level (Dabrowska and Dabrowski, 1990).
|
|
|
|
Li and Robinson (1994) fed catfish diets containing either 0, 145 or 2,837 mg ascorbic acid per kg of diet during winter water temperatures (15ƒC to 4.8ƒC, December to March). They found that liver and anterior kidney ascorbate levels decreased over the 15-week feeding period. Fish fed the 145-mg ascorbic acid diet had tissue levels similar to the zero supplementation group. In Atlantic salmon (Salmo salar), the liver ascorbate concentration was shown to decrease during cold temperature periods, a result of reduced feed intake (Sandnes and Waagb¯, 1992). This suggests that dietary levels need to be adjusted upward to combat reduced feed intake during cold water temperatures. Yet, a definitive study needs to be completed.
Increasing water temperature was shown to increase the rate of development of skeletal deformities in ascorbic acid-deficient fish (Ikeda et al., 1983; Sato et al., 1983).
|
|
|
|
Common aquaculture procedures such as netting, handling, disease treatment, transportation and grading are stressful to fish. The elevation of plasma levels of corticosteroids, mainly cortisol in teleost fish, is considered a primary response to stress, as is the secretion of catecholamines. Their release is the start of a sequence of responses that are a necessary part of survival. The biological cost of stress can ultimately lead to reproductive losses, reduced growth, abnormal behavior, and (or) disease (Fletcher, 1997). Corticosteroids are associated with the anterior kidney, where adrenal function is located in the interrenal tissues under the control of pituitary adrenocorticotropic hormone. The anterior kidney is also rich in ascorbate, although reflecting dietary levels. It has been suggested that ascorbate could be used in steroid biosynthesis. It is generally accepted that elevated levels of cortisol can be immunosuppressive, resulting in increased vulnerability to pathogens.
It has been shown that the ascorbic acid concentrations in tissues in fish change during stressful periods (Thomas, 1984). Hussein (1995) found that ascorbic acid eliminated the adverse effect of ammonia on growth of tilapia. Japanese parrot fish (Oplegnathus fasciatus) were fed diets supplemented with 0, 750 or 3,000 mg of ascorbic acid per kg. When the fish were stressed by intermittent exposure to hypoxia, the fish fed the highest ascorbic acid diet were barely affected by the stressor (Ishibashi et al., 1992b). Juvenile gilthead sea bream (Sparus auratus) fed diets containing 900 mg of ascorbic acid grew better and survived better when stressed following exposures to reduced oxygen levels (Nunes et al., 1996). Waagb¯ and Sandnes (1996) evaluated the effects of vitamin C on smoltification in Atlantic salmon. Although there was no difference in growth rate and body length distribution between fish fed diets containing 20, 60 or 1,000 mg ascorbic acid per kg, the level of serum cortisol was generally lower in fish fed a high level of vitamin C throughout smoltification, thus indicating a stress-ameliorating effect (Waagb¯ and Sandnes, 1996).
In contrast, there was a more pronounced increase in plasma cortisol concentration after stress in carp fed large doses of ascorbic acid (Dabrowska et al., 1991). Vitamin C was not found to help channel catfish fry cope with stress (Li et al., 1998). Nor did vitamin C have any observable effect on the tolerance of catfish for stress induced by confinement (Mazik et al., 1987).
Nitrite is an intermediate product of nitrification and may reach toxic levels in intensive aquaculture systems. Catfish fed diets containing high levels of vitamin C (7,800 mg per kg) had a lower incidence of nitrite-induced methemoglobin (Wise et al., 1988).
A beneficial interaction between increasing dietary levels of astaxanthin and ascorbic acid was demonstrated for Penaeus monodon survival after osmotic stress (Merchie et al., 1998).
|
|
|
|
Wounds in fish can result from various physical factors or from infections. Wounds negatively affect fish health and the quality of fish as food. Collagen formation is necessary for optimal wound repair in animals, hence the interest in the role of vitamin C in wound healing.
Halver et al. (1969) studied wound healing in rainbow trout and coho salmon. Fish were fed diets containing 0, 50, 200, 400 or 1,000 mg ascorbic acid per kg of diet and a 1-cm incision was made through the abdominal wall at the mid-line, with a similar wound made into the musculature above the lateral line. After three weeks of the experimental diets, histologic examination of the wounds suggested that 1,000 mg ascorbic acid per kg diet is needed for optimal wound and tissue repair (Halver et al., 1969, 1975; Halver, 1972; Ashley et al., 1975).
Lim and Lovell (1978) studied wound repair in channel catfish. In this study, wound repair was faster than in the study by Halver et al. (1969) and showed almost complete healing of deep muscle in 10 days when fed 60 mg ascorbic acid per kg.
|
|
|
|
Ascorbic acid deficiency in broodfish affects lipid metabolism and serum vitellogenin level (Waagb¯ et al., 1989), egg quality (Sandnes et al., 1984; Eskelinen, 1989), fry survivability (Blom and Dabrowski, 1996). Sandnes et al. (1984) reported that diets of rainbow trout broodstock need to supply adequate vitamin C to provide eggs with more then 20 µg ascorbic acid per g wet weight.
Numerous studies have pointed to a higher vitamin C demand during reproduction in fish. Supplementation of broodstock diets with vitamin C higher than that required for growth has been shown to improve hatchability and fry condition of tilapia (Oreochromis mossambicus) (Soliman et al., 1986b); sea bass (Dicentrarchus labrax) (Terova et al., 1998); gilthead sea bream (Sparus auratus) (Terova et al., 1998); and rainbow trout (Oncorhynchus mykiss) (Dabrowski and Blom, 1994; Blom and Dabrowski, 1995a).
Others have not found a benefit of higher levels of ascorbic acid in broodstock diets on egg quality (Mangor-Jansen et al., 1994).
There is a rise of seminal ascorbic acid and ovarian ascorbic acid, during vitellogenic growth (Sandnes, 1984; Dabrowski, 1991b; Dabrowski and Ciereszko, 1996a, b). Blom and Dabrowski (1995a) found that 350 mg of ascorbic acid was required per kg of broodstock diet to achieve 90% saturation of ova. Dietary levels of ascorbic acid that are higher than those to meet the growth requirement are needed to optimize seminal ascorbic acid concentration (Blom and Dabrowski, 1995a, b; Ciereszko and Dabrowski, 1995; Ciereszko et al., 1996; Dabrowski and Ciereszko, 1996a; Liu et al., 1997). It was found that low levels of vitamin C in seminal plasma of rainbow trout were associated with a higher percentage of mortality or abnormal embryos in the offspring (Dabrowski and Ciereszko, 1996a; Ciereszko et al., 1999).
|
|
|
|
When the ontogenetic trend of ascorbate was evaluated in larval fish, it was found that the total ascorbate concentration in the fish body decreases with increasing fish size (Dabrowski, 1992a).
Broodstock of sea bass (Dicentrarchus labrax) or gilthead sea bream (Sparus auratus) were fed diets containing either 360 or 2,000 mg of ascorbic acid per kg and the effect on embryo and larval development was assessed (Terova et al., 1998). The hydroxyproline-to-proline ratio and hydroxylysine was found to be higher in the embryos and larvae from broodfish given the higher supplement of vitamin C (Terova et al., 1998).
Enrichment of Artemia with an emulsion containing 20% ascorbyl palmitate, to provide 1,600 mg ascorbic acid per g dry weight Artemia, resulted in better growth of Clarias gariepinus larvae (Merchie et al., 1997). Enrichment of Artemia with ascorbyl palmitate beyond the basal level of 500 mg ascorbic acid per kg dry weight did not improve the growth of turbot (Psetta maxima) larvae, but enrichment with 2,600 mg ascorbic acid per kg dry weight did improve pigmentation rate (Merchie et al., 1996a). Feeding Atlantic halibut (Hippoglossus hippoglossus) larvae diets containing either 300, 2,000 or 3,000 mg ascorbic acid per kg had no benefits on growth or survival (MÊland et al., 1999).
Rotifers (Brachionus plicatilis) fed on microalgae or bakerís yeast were found to be enriched with ascorbic acid (Brown et al., 1998). The ascorbic acid concentration in microalgae commonly used in mariculture ranged from 0.11% to 1.62% of dry weight (Brown and Miller, 1992; Brown et al., 1997, 1998).
|
|
|
|
Knowledge of fishesí immune system is still very limited but growing. The immune system is a complex group of systems working together to protect the organism. Many things, both biotic and abiotic, can affect the immune system and how efficiently it works. The reader is directed to these papers that deal with nutrition and the immune system in fish: Anderson (1984), Blazer and Wolke (1984a, b), Landolt (1989), Sandnes (1991), Lall and Olivier (1993), Waagb¯ (1994), Bowers (1997) and Olivier (1997). For papers that provide details on immunologic procedures, see Leith et al. (1989), Verlhac and Gabaudan (1994), and Verlhac et al. (1998).
Fish are the most primitive vertebrates and are an important link between invertebrates and higher vertebrates. They possess the nonspecific defense mechanisms of the invertebrates, such as the phagocytic mechanisms developed by macrophages and granular leukocytes, but they were also the first animals to develop both cellular and humoral immune responses mediated by lymphocytes. The main lymphoid organs of fish are the anterior kidney, the thymus and the spleen. Nonspecific immunity is considered the first line of defense in fish and represents a considerable part of the immune response, in contrast to mammals.
Fish have adapted to their aquatic environment by developing efficient physical and chemical barriers such as skin and mucus as a first line of defense. The skin represents an important nonspecific defense mechanism to prevent microorganisms from entering to the body. The integrity of the skin is of great importance, and wound healing is therefore much faster than in mammals.
Another important barrier is the mucus, which helps in preventing microorganisms from entering to the body through the skin, gills and gastrointestinal mucosa. The mucus prevents bacteria from adhering to epithelial cells. Furthermore, several components of the nonspecific immune response are found in the mucus, emphasizing its importance as a first defense mechanism (i.e. natural antibodies, lysozyme, lysins, complement).
Many factors can influence the immune response of fish. Among them are stressors and environmental factors of natural origin. Nutrients, micronutrients, and substances of no nutritional values can also modulate the immune response. Depending on their type, the amount and the duration of exposure, their effect can be either negative or positive. Substances with immunostimulating properties can compensate the immunodepression caused by other factors, e.g. the immunodepression caused by a stressor can be compensated by an increased intake of vitamin C before a predictable stress event such as grading (Figure 1 and Figure 2).
|
 |
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
Antioxidant vitamins such as vitamins C and E have been demonstrated to have immunomodulatory properties when fed at elevated doses. Carotenoids in the diet have also been demonstrated to improve the health status of pigmented fish. Tables 2, 3 and 4 are a literature review of the studies concerning the effect of vitamin C on immune response and disease resistance in fish. When a positive effect has been demonstrated, the related study has been shadowed. The doses (mg of vitamin C per kg of feed) at which the effect has been observed are written in bold characters. Treatments without vitamin C supplementation are normally not quoted in the tables.
|
 |
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
view references
|
|
|
|
|
