Effect Of Four Rapeseed Cake/Meal On Growth,Physical And Biochemical Indicators Of Genetically Improved Farmed Tilapia (GIFT), Oreochromis Mossambicus

Rapeseed meal and rapeseed cake are the byproducts of processed rapeseed. As the important source of dietary protein in animal feed, they have been widely studied in fish as well as animal nutrition in general. Rapeseed is been produced worldwide, with the major producers being; Canada, China, India, Australia, United Kingdom and the United States. In the present study three countries were chosen as representative, which include China, Canada and Australia. Four rapeseed meal were prepared, Chinese rapeseed meal, Chinese rapeseed cake, Australia rapeseed meal and Canada rapeseed meal and their nutrients and antinutritional factors were evaluated. In order to provide the scientific basis for the reasonable application of rapeseed in tilapia feed, growth, feeding, body composition, digestive enzymes ability and antioxidant capacity of tilapia (GIFT) were studied.20tilapia sized45.9±0.2(mean±SD) were randomly selected and stocked in concrete tanks filled with water and well supplied with frequent aeration (dissolved oxygen7-9g/L), temperature (20-28℃). Three isonitrogeneous and isolipidic rapeseed diets from each of the four rapeseed meal were prepared at ratio of23%(low),36%(medium) and49%(high) and fed to stocked tilapia. After64days of feeding, the results obtained were as follows;· The features of the four rapeseed meal were;(1) Chinese rapeseed meal: low moisture, low fat, low ash, low protein solubility and higher amount of isothiocyanates.(2) Chinese rapeseed cake:Low moisture, high fat, high ash content, high protein solubility and highest amount of isothiocyanates.(3) Australia rapeseed meal:High moisture, low ash, low protein solubility and low amount of isothiocyanates.(4) Canada rapeseed meal:High moisture, low fat, low ash, high protein solubility and lowest amount of isothiocyanates· Feed intake:Canada rapeseed meal had the best feed intake followed by Chinese rapeseed meal and Australia rapeseed meal, Chinese rapeseed cake had the worst feed intake.· Growth performance:(1) Canada rapeseed meal was the best in terms of feed palatability, weight gain rate (WGR) and feed conversion ratio (FCR) at23%level of inclusion. Up to36%ratio can be used in tilapia diets without affecting feed palatability, feed intake as well as weight gain rate.(2) Chinese rapeseed meal at23%ratio was not significant difference with Canada rapeseed meal at the same ratio in terms of feed palatability, weight gain rate and feed conversion ratio.(3) Australia rapeseed meal at23%ratio was the second to Canada rapeseed meal (23%) in feed intake and weight gain rate.(4) Chinese rapeseed cake was the worst in all three aspects and all three ratios were lower than the rest of the groups.(5) With the increased levels of inclusion in all four rapeseed meal/cake, the rate of dry matter, protein, fat, moisture and ash were decreasing.· Physical indicators:(1) in all four rapeseed meal/cake diets body length and body height decreased as the levels of inclusion increased.(2) Length/height relationship:In Australia rapeseed meal (36%and49%) and Canada rapeseed meal (49%) the L/H relationship was higher than the other groups but there was no significant difference between the other groups.(3) Visceral somatic index:Chinese rapeseed meal had higher VSI reflecting the stomach of tilapia were relatively bigger and the lowest VSI were in Australia rapeseed meal reflecting small stomach.(4) Hepatosomatic index:fish fed with Canada and Australia rapeseed meal lower HIS than that fed with Chinese rapeseed meal and cake. Reflecting that their livers were small and that of Chinese rapeseed meal were big.(5) Condition factor:The highest CF was observed in fish fed with Canada rapeseed meal followed by that fed with Australia rapeseed meal and that of Chinese rapeseed meal and Chinese rapeseed cake were the lowest.· Antioxidant capacity and digestive enzymes ability:(1) In all four rapeseed meal/cake diets, there was an enhancement of antioxidant capacity of tilapia liver when levels of inclusion increased. This may be due to the increased content of isothiocyanates and decreased content of free gossypol in the diets in which isothiocyanates elevated liver SOD and increase its anti-cancer effect.(2) The activity of pepsin and amylase in tilapia intestine were decreasing as the levels of inclusion increased in all four rapeseed meal/cake diets, reflecting decreased in protein digestion and intestinal starch digestion.(3) the activity of lipase of tilapia fed with Canada and Australia rapeseed meal was increasing as the level of inclusion increased and decreased in Chinese rapeseed cake.· By integrating the four rapeseed meal/cake in terms of nutrient composition, tilapia growth performance, nutrient composition, nutrients retention rate, liver’s ability to scavenge free oxygen radicals (SOD), gastrointestinal digestive enzymes activities, the present study drew the following suggestions:(1) Feed intake rate at23%was the best in all four groups, with the Canada rapeseed meal be the first followed by Chinese and Australia rapeseed meal and the last was Chinese rapeseed cake.(2) In tilapia diets application, Chinese and Australia rapeseed meal can be used up to23%level of inclusion.(3) Canada rapeseed meal up to36%is suitable to be used in tilapia diets.(4) less than23%of Chinese rapeseed cake is recommended in tilapia diets.· For the application among the four rapeseed meal/cake in tilapia feed production, the suggestions above with the combination of raw materials prices must be put into consideration.