requirements in Tables 1-3 to 1-13 have again been expressed both as a percentage of dietary protein and on a dry matter basis.

Diets in which the nitrogen component is made up of casein, gelatin, and crystalline amino acids have been referred to in the tables as chemically defined diets. Purified diets are those in which proteins, with an amino acid pattern (g amino acid/16 g nitrogen) that differs substantially from that required, supply the bulk of the nitrogen together with some supplementary amino acids. Natural ingredient diets use normal feed ingredients such as fishmeal, soya meal, blood meal, and wheat middlings.

The values in Tables 1-3 to 1-13 suggest that large differences exist among fish species in their requirements for certain amino acids. Where several estimates are available for one amino acid in a single species, as in the case of rainbow trout (Table 1-8), marked discrepancies occur. Some of these may be due to differences in growth rate, amino acid sources, feed intake, and other aspects of methodology.

For most indispensable amino acids, deficiency is manifest as a reduction in weight gain. In certain species of fish, however, a deficiency of methionine or tryptophan leads to

pathologies, because these amino acids are not only incorporated into proteins but also used for the synthesis of other essential compounds.

Salmonids, including rainbow trout, Atlantic salmon (Salmo salar), and lake trout (Salvelinus namaycush), suffer from cataracts when given a diet deficient in methionine (Poston et al., 1977). The lens begins to become opaque after 2 to 3 months, depending on the extent to which the fish are deficient in sulfur amino acids. As the deficiency increases, lens opacity gradually progresses, causing a large reduction in light transmission. Cataracts also occur as a consequence of tryptophan deficiency in rainbow trout (Poston and Rumsey, 1983; Walton et al., 1984b); the developmental pattern of the cataracts is similar to that occurring in methionine deficiency (Poston and Rumsey, 1983).

Tryptophan deficiency leads to scoliosis (lateral curvature of the vertebral column) and to a derangement of mineral metabolism in certain salmonids, including rainbow trout (Walton et al., 1984b), sockeye salmon (Oncorhynchus nerka) (Halver and Shanks, 1960), and chum salmon (Oncorhynchus keta) (Akiyama et al., 1986). Scoliosis in chum salmon may be reversed by restoring tryptophan to normal concentrations in the diet. The condition may be related to a decline in levels of the brain neurotransmitter serotonin, which is formed from tryptophan. Thus, inclusion of serotonin

Front Matter (R1-R12)

Overview (1-2)

1. Dietary Requirements (3-32)

2. Other Dietary Components (33-37)

3. Antinutrients and Adventitious Toxins (38-42)

4. Digestibility and Absorption (43-48)

5. Diet Formulation and Processing (49-54)

6. Feeding Practices (55-61)

7. Nutrient Requirements Table (62-63)

8. Composition of Feed Ingredients (64-71)

References (72-94)

Appendix (95-102)

Authors (103-104)

Index (105-116)