Evaluating inclusion of commercial pistachio by-product as functional ingredients in rainbow trout fishmeal and plant-meal based diets

Authors: ABANIKANNDA, MOSOPE - University Of Idaho; SHIFLETT, MARK - University Of Kansas; MORAIS, ANA RITA COLACO - University Of Kansas; HONG, JEOUNGWHUI - University Of Maine; Sealey, Wendy; BLEDSOE, JACOB - University Of Idaho

Submitted to: Antioxidants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2024
Publication Date: 10/23/2024
Citation: Abanikannda, M.F., Shiflett, M., Morais, A., Hong, J., Sealey, W.M., Bledsoe, J.W. 2024. Evaluating inclusion of commercial pistachio by-product as functional ingredients in rainbow trout fishmeal and plant-meal based diets. Antioxidants. 13(11), 1280. https://doi.org/10.3390/antiox13111280.
DOI: https://doi.org/10.3390/antiox13111280

Interpretive Summary: The growing demand for sustainable aquaculture requires exploring alternative protein sources for fish diets. However, some alternatives can have negative effects on fish gut health, prompting the need for feed ingredients to mitigate these issues. Pistachio shell powder is a by-product of pistachio nut processing that is rich in antioxidants and prebiotic fiber that together, could potentially contribute to maintaining a balanced and healthy gut in fish fed alternative protein diets. USDA ARS scientists collaborated with colleagues at the University of Idaho to test the potential of pistachio shell powder as a functional feed ingredient in a 12-week study where rainbow trout were fed a traditional fishmeal diet or an alternative plant protein based-diet supplemented with 0%, 0.5%, 1%, or 2% pistachio shell powder. Results indicate that feeding pistachio shell powder alters the gut microbial balance of rainbow trout. However, minimal positive effects on growth of rainbow trout were observed, potentially due to their limited reliance on fiber fermentation for energy.

Technical Abstract: The growing demand for sustainable aquaculture necessitates exploring alternative protein sources for fish diets. However, some of these alternatives can have adverse health effects, prompting research into functional feed ingredients to mitigate these issues. This study investigated pistachio shell powder (PSP), a readily available by-product rich in antioxidants, as a potential functional feed ingredient in rainbow trout diets. The dose-dependent effects of PSP inclusion (0%, 0.5%, 1%, and 2%) on the growth performance, intestinal health, and gut microbiota of rainbow trout were evaluated through administration in either a traditional fish meal (FM) or an ultra-modern plant-meal (PM) based diet. In a 12-week feeding trial, rainbow trout fingerlings were assigned to experimental diets with varying PSP levels. Growth performance, intestinal morphology, gene expression, total antioxidant capacity (TAC), total phenolic compound (TPC), and gut microbiota composition were assessed. PSP significantly (P<0.05) improved average weight gain and daily growth index at the 1% inclusion level in FM diets but did not affect growth in PM diets. No significant (P>0.05) effects were observed on other growth parameters, intestinal morphology, oxidative stress, or inflammatory gene expression, although a trend toward down-regulation was noted in PM diets at 2% PSP. Serum antioxidant capacity and phenolic content were unaffected by PSP inclusion, but TPC increased with higher PSP levels in PM diets. PSP inclusion did not significantly (P>0.05) impact gut microbiota alpha diversity but significantly (P<0.05) altered beta diversity in FM diets at the 0.5% inclusion level. Subtle shifts in community composition were observed in PM diets. Differential abundance analysis revealed taxa-specific responses to PSP, particularly the genus Candidatus Arthromitus increasing in relative abundance with PSP inclusion in both plant meal and fish meal-based diets. Overall, PSP inclusion up to 2% did not elicit significant adverse effects on growth, intestinal health, or antioxidant status. The lack of pronounced effects on gut microbiota and physiological parameters may be attributed to the limited reliance of carnivorous fish on fiber fermentation and complex microbial interactions for energy utilization. Future research should focus on the long-term effects and potential benefits of PSP in herbivorous or omnivorous fish species with longer digestive tracts, aiming to optimize PSP inclusion levels for enhanced aquaculture practices.