Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Natural Resource Management

First Advisor

Michael Brown


Soybean meals (SBM) and its by-products are the most common plant feedstuffs that are used in feeds for a variety of fish species of fish over the last three decades due to high protein levels and good amino acid profile, in comparison with other plant protein sources. In the last two decades the production of soybean was around zero metric tons (Index, 2020). Barley is another plant protein that has been tested in some species diets. While barley is used in many areas such as brewing industry, animal feeding, human consumption, it is mainly used for animal feeding in Kurdistan. Including barley in aqua-feed is potentially important to develop aquaculture because of the high production and low price of barley in Kurdistan. The production of fish meal (FM) is non-existent in Iraq, but annual aquaculture production is growing. For example, global aquaculture production in 2011 was 61.8 million tons and this number increased to 80 million tons in 2016 (FAO, 2018). Fermentation, genetic modification, and extrusion are techniques that have been used to enhance ingredient nutrient values and reduce undesirable compounds in plant-based feedstuffs. In this study, performance (growth and digestibility) trials were conducted to evaluate barley and soybean meals, following additional processing to improve nutritional value, in Rainbow trout (RBT) diets. In Kurdistan the barley production is second top grain production after wheat. The Kurdistan requirement of food fish is 6,700 tons in 2011, however; only 21% of this demand is produced inside this region (IIG, 2013). A 70-day experiment was conducted to evaluate two fermented, co-blends (75% washed soybean meal with 25% washed barley and 50% washed soybean meal with 50% washed barley) to replace fish meal (FM) in juvenile RBT feed. One reference and four treatment diets were fed. Three treatment diets were used to replace 25%, 35%, and 100% of FM with a fermented co-blend (75% of washed soybean with 25% washed barley). An additional diet was formulated to replace 25% of FM with fermented coblend (50% of washed soybean with 50% washed barley). Fish were stocked in 25 tanks (16 fish/tank) providing 320 g (18± 1 g) of biomass per tank in a recirculating aquaculture system (RAS). Non-significant differences were found in survival and growth metrics among all diet treatments. There were no significant differences observed among fish fed treatment diets for organosomatic indices such as the spleen somatic index (SSI), viscerosomatic index (VSI), visceral fat somatic index (VFSI) and hepatosomatic index (HSI). The VFSI value of reference diet was differed significantly in comparing with 100% replacing diet. The results of growth study presented that significant differences were only found between reference and 100% replacing diet. The values of HSI were significantly differed in comparing reference diet with both 100% replacing diet and 25% replacing diet by fermented co-blend (50% of washed soybean with 50% washed barley). In conclusion, FM can be replaced up to 35 % by fermented co-blend (75% of washed soybean with 25% washed barley) and 25% by fermented coblend (50% of washed soybean with 50% washed barley) without any significant negative in growth performance. Non-significant effects realized between all diets for intestine morphology tests. A second study (155 days) was done to compare performance of novel soybean (termed Triple Null, TN) and a conventional variety (Davison, DV) in RBT diets as potential ingredients for the RBT aqua feed industry. Twenty age-0 RBT (~24 g each) were reared in 187 L, semi-square tanks of a 7,500 L RAS. The number of replication per diet was 5. Four diets were formulated to include 20% of TN solvent-extracted and extruded SBMs and similarly processed conventional SBM (DV), along with reference diets. All diets were included almost same level of protein, lipid, energy and ash. Rearing conditions, such as pH, oxygen, and temperature, were optimum for RBT. There was no significant difference among treatments for each of gain rates such as Specific growth rate (SGR) % and relative growth (RG) %, and feed efficiency. In addition, all diets did not significantly differ for each of SSI, VSF, VFSI and HSI indices, and distal intestine histological scores. In conclusion, all ingredients tested in this study can be included in RBT diets up to 20% without any significant effects of fish growth and health performance. Further, a 21-d digestibility trial was conducted to determine to know the level of protein digestibility in RBT diets. One hundred RBT (300 g each) were stocked into each of the six 756-L tanks of ~6000-L RAS. The duration of study was 21 day. Fecal samples were collected three times per diet. No significant difference was found among all diets for protein digestibility. In conclusion, plant protein such as soybean and barley can be used in the carnivorous fish like RBT as an economical protein sources compare to FM. Using some processes such as using extrusion with temperature and fermentation can be a proper way to improve plant protein as a protein source or FM replacement in RBT diet. Using genetic modified to reduce anti-nutritional factors was not results in improving using soybean in RBT diet in comparing with conventional soybean. Fermentation is a process used to improve the nutrition value of soybean and barley due to increasing the protein content and reducing carbohydrate content in barley and soybean meal.

Library of Congress Subject Headings

Rainbow trout -- Feeding and feeds.
Plant proteins as feed.
Soybean meal as feed
Barley as feed.



Number of Pages



South Dakota State University



Rights Statement

In Copyright