THE EFFECTS OF DIFFERENT LEVELS OF CANOLA OIL DIETS ON GROWTH PERFORMANCE AND PROXIMATE COMPOSITION OF NILE TILAPIA Oreochromis niloticus
Introduction
Fish oil is an important energy source for aquaculture feeds (Mulligan and Trushenski, 2013). However, the use of alternative vegetable oils in aquaculture feeds has gained more importance in recent years, because fish oil is costly and can not be found easily (Turchini et al., 2009). Due to the annual increase in the production of tilapia, the use of vegetable oil in feeds has become inevitable for tilapia producers (Ng, 2005). The amount of tilapia production by the year 2020 is estimated to be 8.9 million metric tons (Tacon and Metain, 2008). The present study aimed to determine the growth performance and proximate composition of tilapias fed with different levels (0, 25, 50, 75 and 100%) of canola oil in their diets.
Materials and Methods
Fifteen net cages (1x1x1m dimensions and 1x1cm mesh size) were fixed to a platform in the middle of the concrete pool (240 m2 surface area and 2 m depth). The twenty five Oreochromis niloticus (initial mean weight; 10.00 g) juveniles were randomly stocked into the each net cages as three replicates. The fish were hand-fed to visual satiety three times a day (08:00, 12:30 and 17:00) over the course of experiment (60 days). The oxygen level, water temperature and pH value were 5.9±1 mg/L, 23.3±1 oC and 7.5±1, respectively and water flow was 3 L/min during the experimental period. Five iso-nitrogenic (30% crude protein) and iso-lipidic (12% crude lipid) diets were formulated. Fish oil (FO) was replaced with canola oil (CO) at 0% (FO), 25% (CO 25), 50% (CO 50), 75% (CO 75) and 100% (CO 100) substitution levels. An initial sample of 30 fish from stock pond was taken at the begining of the experiment. After 60 days, 10 fish from each cage were randomly sampled for the proximate analysis and body indices.
Results
At the end of the experiment, there were no significant differences in final weight and specific growth rate (SGR) among the experimental groups. The lowest feed conversion ratio (FCR) was found in FO group and canola groups were similar with each other. Protein efficiency ratio (PER) and lipid efficiency ratio (LER) were significantly higher in FO than the other groups (P <0.05) (Table I). Significant differences were observed in proximate composition among the groups, but there was no difference in body indices values (Table II).
Discussion
Favourable results, in particular in terms of growth performance and feed utilization, were obtained for Nile tilapias in studies where vegetable mixtures or specific vegetable oils were used instead of fish oil (Ng, et al., 2006; Szabo et al., 2011). In some studies set up with the same objective, the growth performance of fish exhibited similarities with the results obtained in the present study; no differences were observed in Nile tilapias (Mulligan and Trushenski, 2013) and red hybrid tilapias (Ng, et al., 2013). In previous studies, similarities and/or differences were observed in the protein and lipid composition of the fish, depending on the lipid and protein content of the feeds. In the present study, it was determined that substituting canola oil with fish oil in different ratios did not adversely affect growth performance and nutritional composition, and that feed utilization had a low effect among the groups.
Acknowledgement
This work was supported by the Scientific Research Project Unit of the University of Cukurova, Turkey under grant no SUF2009BAP16.
References
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