Valorizing Hempseed Meal as a Circular Bio-Ingredient for Sustainable Fisheries Development

The increasing demand for sustainable aquafeeds necessitates the development of alternative protein sources that support both economic efficiency and ecological responsibility. This study evaluates the potential of using hempseed meal (a nutrient-dense agro-industrial by-product) as a functional ingredient in carp aquaculture diets. The paper presents a proof-of-concept evaluation demonstrating the potential of hempseed meal as a circular bio-ingredient that aligns with the principles of sustainable aquaculture, rather than providing a comprehensive assessment of its long-term physiological effects on fish. A 90-day feeding trial was conducted under controlled pond conditions to assess the effects of graded hempseeds meal inclusion levels on growth performance, feed utilization, and environmental sustainability indicators for three Cyprinus carpio varieties. Four isonitrogenous and isoenergetic diets were formulated: a control diet (R1) based on conventional plant protein sources such as soybean and pea meal, and three experimental diets containing 5%, 10%, and 20% hempseed meal (R2–R4). Growth indices including absolute weight gain (WG), average daily gain (ADG), specific growth rate (SGR), and feed conversion ratio (FCR) were determined, and data was analyzed via two-way ANOVA with Tukey HSD post hoc testing. Results indicated that 10% hempseed meal inclusion produced optimal growth responses, improving specific growth rate by 12.6% and reduced feed conversion ratio by 10.8% compared to the control. The most pronounced effects were observed for Frăsinet carp variety (SGR 1.23%·day −1 ; FCR 1.39). Environmental assessments demonstrated that substituting conventional protein sources (soybean and pea meal) with hempseed meal at 20% inclusion valorized 200 kg of hemp press cake per ton of feed, reduced conventional protein use by 33.3%, diverted up to 80% of waste from disposal. These findings validate hempseed meal as a sustainable, cost-effective, and nutritionally viable alternative to conventional protein sources in freshwater aquaculture, advancing circular bioeconomy strategies and supporting low-carbon fish production systems.