Youling Gao defended his thesis on May 6th 2011

Ane Gro Siri Skjelfjord

Improved nutritional value of fish feed with plant protein ingredients by means of organic acid salts and solid state fermentation

Abstract from the thesis - PhD thesis 2011:23

The objective of this work was to improve the nutritional value of plant protein sources to be used in fish feed by means of organic acid salts and solid state fermentation (SSF). Four studies were conducted to determine the effects of a blend of organic acid salts (OAB) in diets for rainbow trout (Oncorhynchus mykiss) and Nile tilapia (Oreochromis niloticus), SSF rapeseed meal in different types of diets for Nile tilapia, and thermal-hydro (steam) treatment on nutritional value of fermented rapeseed meal in diets for Nile tilapia.

The first study was designed to evaluate the effects of adding an OAB (a mixture of sodium formate and butyrate) to a fish meal-based diet and a diet where 36% of the fish meal protein had been replaced by plant proteins (a mixture of soybean meal and pea protein concentrate). The diets were fed to rainbow trout reared in freshwater. Adding OAB to the plant protein-based diet before extrusion significantly reduced the digestibility of dry matter, organic matter, crude fat, and most amino acids. Supplementation of OAB after extrusion reduced the digestibility of crude fat both in the fishmeal and plant protein-based diets. Inclusion of OAB in both fishmeal and plant protein-based diets before extrusion significantly increased feed conversion ratio (FCR), and middle intestine to body weight ratio. Partly replacing fishmeal with plant proteins reduced the digestibility of dry matter, organic matter, crude fat, phosphorous and several amino acids, and increased FCR.

The second study was carried out to determine the potential of laboratory-scale aerobic SSF with Aspergillus niger to increase the nutritional quality of rapeseed meal, and to evaluate the potential for use of untreated (RSM) and fermented rapeseed meal (FRSM) in diets for Nile tilapia. In Exp. 1, three moist diets were produced: a diet based on fish meal and soybean meal (SBM), and two diets in which SBM was fully replaced by RSM or FRSM. In Exp. 2, three extruded diets were produced with the same formulation as used in Exp. 1. Phytic acid and glucosinolates in RSM were reduced, the content of crude protein increased and total amino acids was decreased by SSF. In Exp.l, the growth rate of fish fed the SBM diet was significantly lower than that of tilapias fed the RSM and FRSM diets. FCR of fish fed RSM diet was significantly poorer than that of fish fed the SBM and FRSM diets. Fish fed the RSM diet had significantly higher whole body protein than fish fed the SBM diet. In Exp. 2, the growth rate showed no significant difference among the dietary treatments, while FCR differed among all 3 treatments (SBM

The third study was conducted to evaluate the effects of supplementing the OAB to the diets, in combination with medium-scale SSF of RSM on growth performance and apparent nutrient digestibilities in Nile tilapia. The results showed that supplementing diets with the OAB did not have other effects than increasing the stomach weight in percentage of body weight. SSF of RSM reduced the feed intake, growth rate, liver weight percentage, increased stomach weight percentage and FCR, and reduced whole-body dry matter, crude fat and increased ash contents.

The fourth study was conducted to evaluate the effect of short-term steam treatment for pasteurisation of FRSM on growth performance, whole body composition and apparent nutrient digestibilities in Nile tilapia. Two diets were prepared with and without steam treatment after SSF of RSM. Steam treatment increased FCR, while growth rate, nutrient digestibilities and protein retention were not affected.

In conclusion, supplementing the diets with an OAB did not improve the growth performance of rainbow trout and Nile tilapia. Laboratory-scale SSF of RSM changed the nutritional value and improved the FCR when used in a moist diet, while less efficient FCR was found when used in an extruded diet. Medium-scale SSF of RSM reduced growth rate, but improved FCR. Short-term steam treatment did not improve the nutritional quality of FRSM as a dietary ingredient for Nile tilapia.

Updated: 20.06.11
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