The need for sustainable aquaculture practices has intensified the search for alternative protein sources to replace fish meal (FM) in feeds due to its limited availability and cost implications. Over time, soybean meal (SBM) has been successfully used as a replacement; however, it has some limitations, including rising costs and anti-nutritional factors that can impact fish growth and health. Hempseed meal (HSM) is an industrial by-product of oil extraction from Cannabis sativa and has emerged as a potential feedstuff that is rich in protein, sulfur amino acids, and alpha-linolenic acid (omega-3). However, its potential in carnivorous fish diets remains largely unstudied. Therefore, this study evaluated two commercial HSM products, P30 (~30% protein) and P50 (~50% protein), as partial replacements for SBM in diets for juvenile largemouth bass (LMB), a high-value carnivorous species with expanding domestic and international markets.
Five isonitrogenous and isolipidic diets were formulated: a FM-based reference (FM35), an SBM-based control (CTL), and three experimental diets containing either P30 (P30), P50 (P50), or a combination of P30 and P50 (P30/50) at 20% inclusion partially replacing SBM in the CTL. Groups of 20 feed-trained LMB juveniles (5 g/fish) were stocked into 25 110-L aquaria operating as a recirculating aquaculture system. Fish in each of five aquaria (n=5) were fed one of the randomly assigned diets twice daily for 10 weeks.
Survival was nearly 100% in all treatments. As shown in Table 1, significant treatment effects (P≤0.05) were observed for final weight (FW), weight gain (WG), feed conversion ratio (FCR), and feeding rate (FR). The diets containing HSMs supported growth and FCR of LMB statistically comparable to CTL despite replacing a substantial portion of SBM. Fish fed the FM35 diet displayed lower FR than diets containing P30 and/or P50, and lower FW and WG than all other treatments. Results on whole-body composition and liver antioxidant enzymes will be presented.
These findings provide evidence about the applicability of the hemp ingredients evaluated in aquaculture feeds. Both P3 and P50 can be used to partially replace SBM in LMB feeds.