Certain aspects of amino acid nutrition and metabolism in fish appear to differ from those observed in other vertebrates. Fish are normally fed diets containing 2-4 times as much protein as other vertebrates. This is due to the fact that the optimal dietary protein level required for maximum growth of various cultured fish ranges from about 300 to 550 g crude protein kg-1 diet (Tacon and Cowey, 1985; Bowen, 1987; Wilson, 1989). This observation has led certain investigators, including myself, to suggest that the efficiency of protein utilization is lower in fish than other animals.
Tacon and Cowey (1985) first noted that the dietary protein requirements of fish are not that dissimilar from those of other vertebrates when expressed relative to feed intake (g protein kg-1 body weight day-1) and live weight gain (g protein kg-1 live weight gain). Bowen (1987) has compared several parameters relating protein intake to growth of fish and other vertebrates and found very little difference in protein utilization among the species compared (Table 23.1). The data used in making this comparison included median values for 18 studies for fish and eight studies of other vertebrates, i.e. calf, chicken, lamb, pig and white rat. The only parameters that differed significantly were the level of protein in the diet required for maximum growth and feed efficiency. When the protein requirement data were recalculated to correct for differences in relative protein intake and growth rates, as suggested by Tacon and Cowey (1985), the resulting data were very similar for fish and other vertebrates, thus indicating that the efficiency of protein utilization is very similar among the species compared.
The first definitive studies on amino acid nutrition of fish were conducted in the late 1950s and early 1960s with Chinook salmon, Oncorhynchus tshawytscha. The initial amino acid test diets were formulated to simulate the amino acid content of chicken egg protein, chinook salmon egg protein and chinook yolk-sac fry protein (Halver, 1957). The diet with an amino acid profile based on chicken egg protein gave the best growth rate and feed efficiency. This diet was then used to determine the qualitative amino acid requirements of chinook salmon (Halver et al., 1957).
Table 23.1. Comparison of various parameters relating protein intake to growth offish and other vertebrates. (Data from Bowen, 1987.)
Parameter Fishes Other vertebrates
Specific growth rate 2.765 2.445
Protein in diet (g kg-1) 403 200
Protein intake at maximum growth 16.5 12.0 (mg protein ingested g_1 body wt day-1)
Protein retention efficiency 31.0 29.0
(100 x g protein retained g-1 protein ingested)
Protein growth efficiency 1.945 1.965 (g growth g-1 protein ingested)
Feed conversion efficiency 0.78 0.26 (g growth g-1 diet ingested)
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