low in muscle and brain. These findings suggest that not only dietary protein level and amino acid profile, but also dietary fat level affects the levels of certain FAA of rainbow trout tissues. q 2000
Elsevier Science B.V. All rights reserved.
Keywords: Casein; Free amino acids; Gelatin; Oncorhynchus mykiss; Plasma; Tissue
1. Introduction
Ž .
The concentration of free amino acids FAA in animal tissues can be an sensitive tool to determine the adequacy of dietary amino acids and to estimate the amino acid
Ž .
requirement of the animal Pion, 1976 . In fish, levels of FAA in tissues are also known Ž
to be affected by dietary protein quality Nose et al., 1978; Kaushik and Luquet, 1980; .
Ž .
Dabrowska, 1984 , and a relationship between tissue essential amino acid EAA levels Ž
and dietary requirements has been suggested Cowey and Walton, 1989; Kaushik et al., .
1994; Schuhmacher et al., 1997 . Thus, tissue FAA levels in fish may be useful to know sufficiency of amino acids in practical feeds containing various protein sources.
The influence of dietary protein levels on tissue FAA levels has been examined in Ž
rainbow trout Cowey et al., 1977; Yokoyama and Nakazoe, 1991; Yokoyama et al., .
Ž .
Ž .
1994 , masu salmon Ogata and Murai, 1994 , and European eel Ogata et al., 1985 . These studies have shown, in general, that the tissue EAA levels tended to increase as
the dietary protein level increased. In channel catfish, the serum FAA levels of fish fed diets with various protein to energy ratios were compared, and the effect of dietary
Ž .
Ž .
energy fat level was found to be insignificant Wilson et al., 1985 . Since there is a Ž
. slower rate of protein turnover in muscle than in other organs Fauconneau, 1985 , the
influence of dietary treatments, especially dietary amino acid profiles, may be more responsive in other tissues than muscle. As most studies have examined the influence of
dietary treatments on FAA levels of blood andror muscle, the influence on FAA levels in other tissues should be examined.
On the other hand, the relationships between dietary amino acid patterns and tissue FAA patterns have been evaluated in several fish species, and the results have shown
that a high correlation exists between dietary and plasma EAA patterns in common carp Ž
. Ž
Plakas et al., 1980; Dabrowski, 1982; Ogata, 1986 , rainbow trout Nose, 1973;
. Kaushik and Luquet, 1977a; Walton and Wilson, 1986; Murai et al., 1987 , and some
Ž .
other species Lyndon et al., 1993; Kaushik et al., 1994 . As the correlations in most of these studies were determined using only one diet or several diets having similar amino
acid profiles, it is not clear whether such high correlations exist when different dietary treatments are fed.
As the first step to estimate quantitative adequacy of amino acids in practical fish feeds by comparing tissue FAA levels, we examined in this study the influence of
different dietary compositions on FAA levels of several tissues in rainbow trout. We conducted a 6-week feeding experiment using six semi-purified diets containing differ-
ent levels of protein, fat, and amino acids. Then, we compared FAA levels in plasma, liver, dorsal white muscle and brain. Relationships between dietary amino acid patterns
and tissue FAA patterns were also evaluated.
2. Materials and methods
