Ž .
in fecal matter of fish fed soy-based diets than in fish fed FM-based diets 9 vs. 27 . Results from this study show that a significant part of FM can be replaced by soy proteins for
low-pollution diets, without compromising weight gain or feed efficiency in large rainbow trout fed practical diets. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Fish meal; Soybean; Phosphorus; Phytase; Algal availability; Rainbow trout
1. Introduction
Ž .
Fish meal FM supplies the largest part of dietary protein for salmonid culture. Alternative protein sources have been studied intensively for at least two reasons.
Firstly, long-term scenarios indicate an increasing demand for the world fisheries catch. In salmonid cage farming, feed costs represent around 50 of the operating costs
Ž .
Tveteras and Bjørndal, 1998 , of which the largest single cost derives from protein
˚
feedstuffs. Higher global demand for fish landings may increase the price of FM, which was recently demonstrated during the decline in catches due to the latest El Nino.
˜
Ž . Secondly, the need to formulate diets which minimize phosphorus P excretion of fish
and consequent eutrofication of waters requires replacement of FM with low-P protein Ž
. sources Lall, 1991 . Suitability of soybean products to partially replace FM has been
Ž assessed for cost-effective, sustainable and low-P fish feed formulations e.g., Murai,
. 1992; National Research Council, 1993 . Soybean products vary in their nutrient and
Ž .
antinutritional factor ANF contents and distinct fish species and size-related differ- Ž
ences in nutrient requirements and tolerance to dietary ANF exist National Research .
Council, 1993 . Therefore, careful review of available data on the nutritional value of soybean products to a given husbandry condition is necessary.
Processing of soybeans into various meals, concentrates and isolates has a major Ž
. influence on their nutritional properties Wolf and Cowan, 1971 . Growth and feed
Ž .
utilization responses of rainbow trout to replacing FM for soybean meals SBM and Ž
. soybean protein concentrates SPC have been reported in more than 30 scientific
papers. SPC has successfully partially replaced FM in studies by Olli and Krogdahl Ž
. Ž
. Ž
. Ž
. 1994 , Pfeffer and Henrichfreise 1994 , Kaushik et al. 1995 and Medale et al. 1998 ,
´
Ž .
whereas weight gain reduction was reported by Rumsey et al. 1993; 1994 , Stickney et Ž
. Ž
. al. 1996 and Kim et al. 1998 . In contrast to SPC, SBM has more frequently been
Ž assessed as an inferior protein source to FM e.g., Pfeffer and Beckmann-Toussaint,
. 1991; Davies and Morris, 1997 . However, SBM replaced 25, 30 and 40 of the
Ž .
Ž .
FM protein according to Dabrowski et al. 1989 , Oliva-Teles et al. 1994 and Sanz et Ž
. al. 1994 , respectively, with no decrease in weight gain of fish. That growth perfor-
mance of SPC-fed fish has been better than SBM-fed fish may be attributed to a decrease in the content of several ANF, including oligo-, di- and polysaccharides
Ž .
Liener, 1994 . Ž
. Murai et al. 1989 suggested that fish weight affects utilization of soy flour by
fingerling rainbow trout. Most of the experiments have been conducted in juvenile fish with no trials conducted in fish weighing more than 300 g. Rainbow trout farmed in
Chile, Denmark, Norway and Finland are typically grown to 1–4 kg in both land-based
and sea-cage operations, and feed costs per fish are largest in the final stages of the production cycle. Therefore, more information on alternative protein feedstuffs for large
rainbow trout are clearly needed. Several ANF present in soybeans can be partially removed by proper heat treatment
Ž .
and extraction procedures Liener, 1994 . However, phytate, a cyclic inositol compound containing six phosphate groups, is relatively heat-stable and cannot be effectively
removed without enzymatic reactions. Phytate-bound P is not available to monogastric Ž
. animals including fish National Research Council, 1993 . Furthermore, phytate may
Ž .
interfere with the availability of other minerals Liener, 1994 and can bind trypsin and Ž
. decrease protein availability in fish Singh and Krikorian, 1982; Spinelli et al., 1983 .
Supplemental phytase effectively releases phosphate groups of phytate in rainbow trout Ž
. Cain and Garling, 1995; Rodehutscord and Pfeffer, 1995 , but the benefits of its
supplementation in practical diets, containing high levels of soybean products, has not been reported. In most studies on nutritional properties of SPC and SBM, supplemental
phosphate has been provided to meet or exceed the requirement of rainbow trout. Therefore, the influence of marginal P supply in trout fed soy-based diets has not been
Ž reported. Sub-optimum P supply may induce poor bone mineralization Vielma and Lall,
. Ž
. 1998 , increase carcass fat deposition Eya and Lovell, 1997 and decrease resistance to
Ž .
disease Eya and Lovell, 1998 . In this paper, we report effects of partial replacement of FM for SPC and SBM
Ž .
SPC:SBM protein ratio 4:1 on weight gain, feed efficiency, body composition and nutrient load of large rainbow trout. An attempt was also made to study the algal
availability of dietary and fecal P. The experiment was conducted in adult rainbow trout fed practical, high-energy diets without supplemental phosphate.
2. Materials and methods
