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Canola meal may be beneficial in improving the sustainability of Rainbow Trout

Research Reviewed by Dr. Charles Qin

The most common protein that is used in diets for trout is fishmeal. A large part of the fish available today is produced by the aquaculture industry.  This industry has made huge headway with respect to sustainability. A large portion of this effort has revolved around reducing the use of marine origin fishmeal in diets for farmed fishes.

As Table 1 shows the “fish in fish out” ratio for the most common farmed species. As the table shows, overall the industry provides consumers with 30 million metric tonnes of high quality food from 15 million metric tonnes of marine fish. However, there are differences in this ratio by species, and farming of salmonid fish (trout and salmon) is responsible for the use of about 40% of the fishmeal used by the aquaculture industry.

Table 1. Fish in-Fish-out ratios (FIFO) for Select Farmed Species (million metric tonnes)

wdt_ID Species Group FIFO Farmed Production, MMT Raw Materials Used, MMT
1 Eels 2.7 0.26 0.7
2 Salmonids (salmon and trout) 2.5 2.54 6.4
3 Marine fish 1.6 2.55 4.1
4 Crustaceans (marine and freshwater) 0.7 5.48 3.8
5 Other freshwater fish 0.3 4.05 1.2
6 Tilapia 0.2 3 0.6
7 Fed carp 0.1 12.17 1.2
8 Overall 0.5 30.05 15

www.globalseafood.org/advocate/how-much-fish-is-consumed-in-aquaculture/

Rainbow trout (Oncorhynchus mykiss), members of the salmonid family, are native to lakes and rivers in North America west of the Rock Mountains. They been introduced to bodies of water all over the world. These fish are widely farmed both as a table fish and to stock lakes or rivers for sport fishing. In the wild, Rainbow trout are carnivores and require high protein diets. Reducing the inclusion of fishmeal in the diets of these fish, without reducing feed intake or hampering growth has been the focus of many research studies.

The amino acid balance of protein From canola meal is closer to fish meal than any other vegetable protein source and the best source to serve as a replacement for fish meal (Enami, 2011). Indeed, Slawski et al (2013) determined that canola protein isolate could be used to fully replace fish meal in diets for rainbow trout with no negative effect on palatability, intake or feed efficiency. However, canola protein isolate is not an ingredient that is readily available.

Other research studies have demonstrated that canola meal can be used to replace a portion of the fishmeal in the diet. While the inclusion levels are low due to the higher fiber content of the meal, canola meal has been proven to be an ingredient that can reduce the need for fishmeal for this important species. As Table 2 shows, the digestibility of protein from solvent extracted canola meal is similar to that of fishmeal and extruded vegetable proteins.

Table 2. Digestibility of plant-ingredients by rainbow trout (Burel et al., 2000)

wdt_ID Digestibility, % Fishmeal Canola meal Extruded peas Extruded lupins
1 Dry matter 70.8 66.3 69.7
2 Energy 76.4 68.9 77
3 Protein 89.2 90.9 87.9 96.2
4 Phosphorus 26.4 42.6 61.9

Results from growth studies

In an early study (Shafaeipour et al., 2008) canola meal plus DL-methionine were used to replace from 10 to 57% of the protein from fishmeal in diets for trout with an initial weight of 4.1 grams. At the end of the 16-week long feeding period, the researchers determined that there were no effects of diet on growth, and that canola meal had the potential to replace substantial levels of fish meal in diets for trout.

Yigit et al (2012) provided rainbow trout fry (initial weight 1.5g) with isonitrogenous diets that contained 0, 8, 16, 24 or 32% solvent extracted canola meal for 12 weeks. The canola meal replaced fishmeal and corn flour in the diets. Results are provided in Table 3.

Table 3. Performance of rainbow trout fry with diets containing various levels of canola meal

wdt_ID Performance Parameter Canola meal inclusion level, (0%) Canola meal inclusion level, (8%) Canola meal inclusion level, (16%) Canola meal inclusion level, (24%) Canola meal inclusion level, (32%)
2 Starting weight, g 1.55 1.57 1.56 1.57 1.58
3 Final weight, g 14.21 13.06 12.82 11.79 10.48
4 Weight gain, g 12.65 11.51 11.24 10.2 8.88
5 Specific growth rate, %/day 2.45 2.36 2.3 2.24 2.1
6 Feed intake, g 12.8 12.77 12.55 12.35 11.49
7 Feed efficiency 1.04 1.1 1.09 1.19 1.3
8 Survival, % 98.3 98.3 98.3 98.3 96.6

Performance was acceptable at all levels of canola meal in the diet with no decline in feed intake, and high survival rates with all levels of canola meal inclusion. Although numerically lower, performance parameters obtained with the 8% and 16% inclusion levels were not statistically different from those obtained when the trout received the diet with 0% canola meal.

In a similar experiment, Collins et al (2012) provided rainbow trout with diets in which canola meal was included at 0. 7.5, 15, 22.5 and 30%. Much like the study by Yigit et al (2012) there were linear declines in specific growth rate as canola meal inclusion increased. The researchers suggested limiting the canola meal inclusion level to 15%.

Canola from brown or yellow seed coat canola was included in diets for rainbow tout with an initial weight of 2.5 grams at an inclusion level of 15% (Anderson et al, 2018). Final body weight was slightly lower with the brown seed canola (81 compared to 101g for brown seed canola compared to fish meal) but not with the yellow seed canola. There were no significant differences in specific growth rate of feed efficiency for any of the treatments.

These results demonstrate that practical diets can be formulated using 15% canola meal to reduce the use of fishmeal in diets for rainbow trout. While not a full replacement for fishmeal, inclusion of canola meal at this level would be beneficial in further improving the sustainability of these fish.

References

Anderson, D.M., MacPherson, M.J., Collins, S.A. and MacIsaac, P.F., 2018. Yellow-and brown-seeded canola (Brassica napus), camelina (Camelina sativa) and Ethiopian mustard (Brassica carinata) in practical diets for rainbow trout fingerlings. Journal of applied aquaculture30(2), pp.187-195.

Burel, C., Boujard, T., Tulli, F. and Kaushik, S.J., 2000. Digestibility of extruded peas, extruded lupin, and rapeseed meal in rainbow trout (Oncorhynchus mykiss) and turbot (Psetta maxima). Aquaculture188(3-4), pp.285-298.

Collins, S.A., Desai, A.R., Mansfield, G.S., Hill, J.E., Van Kessel, A.G. and Drew, M.D., 2012. The effect of increasing inclusion rates of soybean, pea and canola meals and their protein concentrates on the growth of rainbow trout: concepts in diet formulation and experimental design for ingredient evaluation. Aquaculture344, pp.90-99.

Enami, H.R., 2011. A review of using canola/rapeseed meal in aquaculture feeding. Journal of Fisheries and Aquatic Science6(1), p.22..

Slawski, H., Nagel, F., Wysujack, K., Balke, D.T., Franz, P. and Schulz, C., 2013. Total fish meal replacement with canola protein isolate in diets fed to rainbow trout (O ncorhynchus mykiss W.). Aquaculture Nutrition19(4), pp.535-542.

Yigit, N.Ö., Koca, S.B., Bayrak, H., Dulluc, A. and Diler, I., 2012. Effects of canola meal on growth and digestion of rainbow trout (Oncorhynchus mykiss) fry. Turkish Journal of Veterinary and Animal Sciences36(5), pp.533-538.

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