Abstract
Aquaculture offers many benefits to the world, the primary of which is that it provides more than 50% of the fish that people eat. Globally, aquaculture is the fastest
growing food industry and the U.S. ranks only 17th in aquaculture production. Mostly
commonly farmed fish species are salmonids such as Atlantic salmon (Salmo salar) and
rainbow trout (Oncorhynchus mykiss) because salmonids are healthier food with good price
and much easier to culture. Traditionally, fish meal is a great nutrient source for salmon it
may not be sustainable. So alternative feed ingredients are needed for sustainable salmonids
industry. Currently, soybean meal (SBM) and soy based proteins are the major ingredients
for commercial fish feed due to their cost and nutrient content with well balanced amino acid
profile. However, for Atlantic salmon, SBM impacts gut health, and triggers soybean meal
induced enteritis (SBMIE) attributed to the presence of anti-nutritional factors (ANFs). ANFs
can negatively impact the distal intestinal histology, reduce nutrient absorption and digestion,
and negatively alter the gut microbiome, compromising the immune resilience and welfare of
salmonids. Therefore, goal of my thesis was to mitigate the SBMIE in Atlantic salmon and
Rainbow trout via using dietary supplementation of function feed ingredient such as black
soldier fly larval meal and feed additive (organic acid, sodium butyrate). I have conducted
two research projects; firstly, using whole black soldier fly meal (WB) as a complementary
ingredient in SBM-based diets has been shown to improve (not significantly) the
performance of Atlantic salmon in terms of growth performance and mitigate the SBMIE. A
total of 630 Atlantic salmon (15 g) were distributed in 21 tanks (triplicates) in a recirculatory
aquaculture system. Seven isonitrogenous (42% crude protein) and isolipidic (20% lipid)
diets: fish meal-based diets (FM), low-level SBM-based diets (LS), SBM+5% and 10%
WBLM (LS-WB5 and LS-WB10), and high-level SBM-based diets (HS), SBM+5% and
10% WBLM (HS-WB5 and HS-WB10) were fed for 12 weeks. Results of the first project
suggest that Atlantic salmon can utilize up to 40% SBM in their diet without compromising
the growth and feed utilization. The histology of the distal intestine showed that there were
no differences in morphological structure among the groups. Conclusively, the current study
has shown that Atlantic salmon could utilize a high level of SBM with no detrimental effects on performance, and the supplementation of WB can mitigate (not significantly) the SBMIE.
Overall, salmon diets can be manufactured with low level of FM and high level of SBM.
The second project of my thesis was focused on using WB meal or organic acid
(sodium butyrate, SB) in SBM based diets to improve the SBM utilization in rainbow trout.
The aim of this study was to investigate the effects of supplementation of WB meal and SB
in SBM-based diets on growth performance, nutrient utilization, and gut health of trout. A
total of nine experimental diets (42% crude protein and 20% lipid): fish meal-based diets
(FM), SBM-based diets (30%SBM and 40%SBM), 30%SBM+5% BSFL, 40%SBM+5%
BSFL, 30%SBM+0.2%SB, 40%SBM+0.2%SB, 30%SBM+5% BSFL+0.2%SB, and
40%SBM+5% BSFL+0.2%SB were fed for 16 weeks. Fish were sampled for growth
performance at 5 weeks, 8 weeks, 12 weeks and 16 weeks. There was no significant
difference in growth at 5th, 8th, and 16 weeks among the groups (p > 0.05). However, at the
12th week, the trout fed SBM40 registered a significantly lower value, while those fed
SBM30+SB recorded a higher response (p<0.05). The feed utilization parameters (feed
conversion ratio and protein efficiency ratio) and hepatosomatic index value did not differ
significantly among the groups. The histological results did show that the trout fed soy diets
appeared to have a loss of vacuolization in the villi and increased lamina propria thickness
within these folds. Shortening and thickening of the folds were most apparent in the SBM40
+ I5, the SBM40 + SB, and the SBM30 + I5 + SB, but the SBM30 + I5 appeared similar to
the control diet. Based on the results obtained in the present study suggested that 5% WB or
0.2% sodium butyrate may be used as a complementary additive in high SBM diets for
rainbow trout. Conclusively, results from my thesis provide a baseline to improve the
salmonids feed industry sustainability.