The potential of rapeseed protein concentrate as fish meal alternative in diets for rainbow trout (initial average weight 37.8 ± 1.4 g) was evaluated. Nine experimental tanks of a freshwater flow-through system were stocked with 12 fish each. Triplicate groups of fish received isonitrogenous (47.9 ± 0.5% CP) and isoenergetic (22.4 ± 0.2 kJ g -1 ) experimental diets with 0, 66 and 100% of fish meal substituted with rapeseed protein concentrate (71.2% CP), thereby providing 0, 29 and 43% of dietary protein. As the amino acid profile of rapeseed protein concentrate was comparable to fish meal, there was no need to supplement experimental diets with synthetic amino acids. At the end of the 84 days of feeding period, fish growth performance, feed intake and feed efficiencies were not compromised, when 100% of fish meal in the control diet was replaced with rapeseed protein concentrate, revealing a SGR of 1.19 or 1.10, a FCR of 1.09 or 1.18 and a feed intake of 78.5 or 74.7 g in fish fed on the control diet or fed the diet devoid of fish meal, respectively. Intestinal morphology did not reveal any histological abnormalities in all dietary groups. Blood parameters including haematocrit and haemoglobin as well as glucose, triglycerides and total protein in the plasma were not different between treatment groups. Thus, the rapeseed protein concentrate tested here has great potential as an alternative to fish meal in rainbow trout diets.

The potential of rapeseed protein concentrate as fish meal alternative in diets for wels catfish (initial average weight 86.5 ± 1.9 g) was evaluated. Sixteen fish were stocked into each of 12 experimental tanks being part of a freshwater recirculation system. Fish were organized in triplicate groups and received isonitrogenous (603 ± 3 g CP kg )1 ) and isocaloric (23.0 ± 0.3 kJ g )1 ) experimental diets with 0%, 25%, 50% and 75% of fish meal replaced with rapeseed protein concentrate (710 g CP kg )1 ). At the end of the 63-day feeding period, weight gain, standard growth rate, feed intake, feed conversion ratio and protein efficiency showed no significant difference between control group and fish fed on diets with 25% reduced fish meal content by inclusion of rapeseed protein concentrate. Higher dietary fish meal replacement negatively affected diet quality and palatability resulting in reduced feed intake, feed efficiencies and fish performance. However, blood serum values of triglycerides, glucose and protein were not significantly different between treatment groups, still indicating a favourable nutrient supply from all experimental diets. KEY WORDS

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The potential of canola protein isolate (CPI) as fish meal alternative in diets for rainbow trout was evaluated. Apparent digestibility coefficients (ADCs) for protein from a fish meal-based reference diet (89.2 ± 1.1%) and CPI (84.6 ± 1.8%) were determined by indirect marker method in a digestibility experiment. ADC of dietary dry matter was slightly lower for the reference diet (62.5 ± 4.7%), but not significantly different to the CPI test diet (65.9 ± 3.1%). In a subsequent growth trial, 20 fish (initial weight 31.5 ± 0.5 g) were stocked into each of 15 experimental tanks of a freshwater flow-through system. Fish were organized in triplicate groups and received experimental diets with 0%, 25%, 50%, 75% and 100% of fish meal replaced with CPI on the basis of digestible protein (designated as Control, I25, I50, I75, I100 respectively). At the end of a 70-day feeding period, growth performance, feed intake and feed conversion ratio of treatment groups receiving diets I25, I50 or I100 were similar to the control group, while fish fed diet I75 showed significantly higher weight gain caused by improved feed conversion. The tested CPI was therefore identified to be a highly valuable fish meal alternative, not negatively affecting diet palatability, feed intake and feed efficiencies.

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-The main problem of the aquaculture sector is the provision of suitable and sufficient fish feed, because the most important protein source in aquaculture, the fish meal, is a limited resource. Due to their high nutritional value the rapeseed proteins have great potential as an alternative protein source for the fish nutrition. Therefore, the aim of this work is to develop a manufacturing process of high quality rapeseed protein concentrates, which can replace the limited marine resource. For this purpose, small pilot scale processing procedures were performed to produce a rapeseed protein concentrate (RPC). The meal for protein extraction was prepared by gentle meal processing. Rapeseed protein fractions were prepared by an aqueous extraction procedure. The obtained protein solution is further purified and then dried. The investigated rapeseed protein extraction process provides RPC with high nutritional value and low levels of antinutritional factors. From the nutritional point of view the produced RPC can be compared with the fishmeal. Its amino acid profile reflects the amino acid demands of fish. The obtained RPC was utilized for experimental setups of fish meal replacement in diets for rainbow trout, turbot, common carp and wels catfish. Experimental results from the conducted feeding trials demonstrate an enormous potential of RPC as protein source in aquafeeds. The highest fishmeal replacement level (up to 100%) was observed in the feeding trials with rainbow trout. Therefore, especially in the nutrition of rainbow trout, RPC was identified as an excellent fishmeal alternative.

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The potential of rapeseed protein concentrate as an alternative to fishmeal in diets for common carp (initial average weight 26.7±0.8 g) was evaluated. Triplicate groups of fish were fed isonitrogenous (40.4±0.2% crude protein) and isocaloric (21.4±0.1 kJ/g) experimental diets with 0%, 33%, 66%, or 100% replacement of fishmeal by rapeseed protein concentrate. At the end of the 56-day feeding period, growth parameters and feed efficiencies did not significantly differ between fish fed the 0% and 33% diets. The 66% and 100% replacement diets led to reduced feed intake and feed efficiency, resulting in lower growth performance. It appears that the taste and amino acid profile of these diets were negatively affected by the high inclusion levels of rapeseed protein concentrate. In conclusion, rapeseed protein concentrate can effectively replace 33% of the fishmeal in diets for carp without using palatability enhancers or amino acid supplements. The IJA appears exclusively as a peer-reviewed on-line open access journal at http://www.siamb.org.il Sale of IJA papers is strictly forbidden.