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Abstract

One of the key research areas in aquaculture nutrition is fish meal replacement.
Plant derived materials such as legume and oilseed meals and protein concentrates
are being investigated and used in aquafeeds. However, the use of these
ingredients is limited by antinutritional factors. Phytate is an important
antinutritional factor that impacts on phosphorus utilisation and excretion in
monogastric animals including fish. Phytate has negative effects on growth
performance, protein and mineral, especially phosphorus, digestibility and
utilisation. Both purified phytic acid and natural sources of phytate were used in
the present study. Different criteria such as growth performance, chemical
composition and nutrient apparent digestibility were measured to assess the effect
of phytate and phytase on Atlantic salmon (Salmo salar, L.). Furthermore, due to
the importance of phosphorus in environmental loading, the effect of phosphorus
intake on phosphorus utilisation was also investigated.
The first experiment established that phytate (0.8%) did not affect feed intake or
growth performance, but significantly reduced protein digestibility without
negative effect on trypsin activity in Atlantic salmon. Phytase per se enhanced the
growth of fish and when phytase and phytate were added together feed efficiency
ratio was higher. Phytase neutralized the effect of phytic acid on protein
digestibility.
Use of phytase in plant meal based diets prevented the negative effects of phytate.
Phytase had positive effects on feed intake, growth, whole-body chemical
composition and nutrient digestibility. When phytase was used in a diet with
sufficient dietary phosphorus, the positive effects ofphytase were not observed.
Efficacy of phytase strongly depends on endogenous and exogenous factors.
Phytase inclusion in a fish meal based diet partially replaced with plant meal had
no effect on fish performance, but when phytase was used in a soy protein
concentrate (SPC) based diet, improved performance was observed. Probably,
phosphorus apparent digestibility is the best criterion for determining phytase
efficacy. Furthermore, phytase had a significant effect on reducing phosphorus waste from a plant protein based diet. Phytase supplementation of diet and pretreatment
of ingredients were compared using a SPC based diet. Supplementation
at levels greater than 1 OOO U phytase kg-1 diet was necessary to improve salmon
performance and phosphorus utilisation, while pre-treatment of SPC with 250 U
phytase kg-1 had similar significant effects.
The effect of phosphorus intake on apparent digestibility of phosphorus was
investigated in Atlantic salmon. Phosphorus apparent digestibility was negatively
correlated with dietary phosphorus concentration. Digestible phosphorus was
approximately the same for salmon in all treatments despite using different levels
of dietary phosphorus that ranged from suboptimal to excess amount. The effect
of feed intake on nutrient and mineral especially phosphorus digestibility was also
investigated. Ration affected nutrient digestibility except energy digestibility in
fish and there were significant correlations between dry matter, protein and
phosphorus digestibilities.
Experiments generally showed that phytase supplementation of diet or pretreatment
of ingredients has the potential to improve growth performance and
phosphorus utilisation of Atlantic salmon and reduce the phosphorus load from
fish farm provided proper experimental design is used. Since dietary phosphorus
concentration and phosphorus intake affect apparent phosphorus digestibility
these factors must be taken into account when conducting phosphorus nutrition
research.

Item Type:	Thesis - PhD
Authors/Creators:	Sajjadi, M
Keywords:	Atlantic salmon, Atlantic salmon, Phosphorus, Phytases
Copyright Holders:	The Author
Copyright Information:	Copyright 2004 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Chapter 2 appears to be the equivalent of a post-print of an article published as: Sajjadi, M. and Carter, C.G. (2004), Effect of phytic acid and phytase on feed intake, growth, digestibility and trypsin activity in Atlantic salmon (Salmo salar, L.) . Aquaculture Nutrition, 10: 135–142. doi: 10.1111/j.1365-2095.2003.00290.x Chapter 3 appears to be the equivalent of a post-print of an article published as: M. Sajjadi, C.G. Carter, (2004), Dietary phytase supplementation and the utilisation of phosphorus by Atlantic salmon (Salmo salar L.) fed a canola-meal-based diet, Aquaculture, 240, 417-431
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