Date of Award
Master of Science
The rapid growth of the aquaculture industry has resulted in a growing demand for fishmeal (FM) and fish oil raising economic and sustainability concerns. Fishmeal and fish oil rely on finite marine sources and increasing reliance on these products continues to raise prices while incentivizing overfishing in order to meet demand. In order to combat the increasing cost and environmental detriment of FM, plant protein sources have grown in popularity as a protein replacement in aquafeeds. Soybean meal (SBM) is one of the more notable protein alternatives due to its high protein content and relatively well-balanced amino acid profile. However, at high dietary inclusions, SBM has been found to have negative impacts on feed ingestion, digestion, and growth rates. Improving feed intake and utilization of alternative protein feeds is an important challenge facing the aquaculture industry. Social environment affects feeding behavior through various means. Further, feeding behavior has previously been shown to have heritable aspects. Thus, the objective of this thesis was to investigate how social environment influences feed intake and feed utilization of a plant protein-based diet and how these effects might be transferred to offspring of the next generation. The first experiment (Chapter 2) investigated the effects of chronic social isolation on zebrafish monoaminergic system signaling, growth performance, feed intake, and intestinal health. Zebrafish were either isolated (CI; one fish, 1.5 L tank) or socially housed (SH; six fish, 9.0 L tank) beginning at 20 days-post-fertilization (dpf) with 18 replicates per treatment group. Social treatments lasted for 30 days and during the final 15 days, zebrafish were challenged with a high inclusion SBM based diet. The results indicated that social treatment did not have an effect on the monoaminergic system or growth performance; however, CI fish consumed significantly more and presented with less intestinal inflammation. This suggests social isolation promoted feed intake and the perhaps increased SBM diet intake led to improved intestinal adaptation to this typically inflammatory diet. The second experiment (Chapter 3) investigated the effects of parental social experience on the feed intake and feed utilization of first generation offspring. Offspring of both CI and SH fish were assigned to one of four groups: CI offspring fed a FM based diet (CIOF), CI offspring fed a SBM based diet (CIOS), SH offspring fed a FM based diet (SHOF), or SH offspring fed a SBM based diet (SHOS). Each treatment group had three replicates and all were socially housed with 25 fish per tank; the feeding trial lasted 30 days. The results showed that CIO fish had significantly higher initial weights and weight gains regardless of diet type. While feed intake tests, appetite-related gene expression, and intestinal health analyses did not provide a clear understanding of why these results occurred, the improved growth performance suggests some influence of parental social experience on offspring quality and feed utilization. Overall, the findings from this thesis suggest that social experience can alter feeding behavior in zebrafish and this may be a useful tool in improving ingestion rates of lower quality diets, such as those with a SBM base. This provides underlying support for further investigation into the use of social isolation as a selective breeding tactic, allowing those in the aquaculture industry to select for optimal health and body condition and potentially create generations of fish better equipped to utilize plant protein alternatives.
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