The use of ocean-caught fish to produce fishmeal, an expensive source of protein for aquaculture feed, threatens ocean fish stocks and biodiversity and creates economic uncertainty for aquaculture businesses. With the continued growth of the U.S. mariculture industry, this project aimed to evaluate the replacement of fishmeal protein with alternative protein sources and to develop the most promising, sustainable, and cost-effective diets using optimized combinations of conventional and non-conventional alternative protein sources for a high-value potential mariculture species, black sea bass (Centropristis striata).

Initially, the team conducted user-inspired research by developing a questionnaire and a low-fidelity prototype to define the user community for the project and to gain a deep understanding of their needs in the aquaculture industry. Fish farm owners clearly stated that their top priorities are the development of sustainable feeds, reducing feed costs, and addressing customer inquiries about how their fish are grown. During the innovation curriculum session in Phase 1, a collaborative team was established to build technical capacity and foundational resources for the development of the finfish mariculture industry. This multidisciplinary collaboration brought together expertise from academia, commercial marine fish farms, feed manufacturer and ingredient suppliers, economist, extension personnel, technology commercialization officers, and commercial end users.

In Phase 1, three feeding trials were conducted to evaluate the nutritional value of two non-conventional protein sources: single cell protein (Methylobacterium sp. JUV-KBM203, KnipBio, Lowell, MA) (Trial 1) and Salicornia virginica (a salt-tolerant halophyte plant) (Trial 2), and to find the best diets in combination with alternative protein sources (Trial 3) for black sea bass juveniles. In Trials 1, 2, and 3, a total of 21 iso-nitrogenous (48% crude protein) and isolipidic (13%) test diets (eight, seven, and six diets, respectively) were formulated and prepared, replacing graded levels of menhaden fishmeal by supplementing single cell protein meal, Salicornia meal, and a combined alternative protein source, respectively. A control diet (0% fishmeal replacement) was formulated with high fishmeal (30%) and other practical protein sources, including solvent-extracted soybean meal and poultry by-product meal. All test diets were prepared at the University of North Carolina Wilmington (UNCW) Finfish Aquaculture Research Lab. Fifteen juvenile fish were stocked in each 75-L tank on a controlled laboratory scale in a recirculating aquaculture system at the UNCW Aquaculture Facility, and each test diet was fed twice a day to triplicate groups of juvenile fish for 8 to 10 weeks. The water quality parameters (dissolved oxygen, pH, water temperature, ammonia, nitrate, and nitrite) were maintained at optimal levels as established for this species. The diets' proximate, amino acid, and fatty acid profiles, growth performance, feed utilization, and body biochemical compositions of fish after each feeding trial were evaluated.

In Trials 1 and 2, supplementing single cell protein and Salicornia meal up to 30% and 15%, respectively, did not affect growth performance compared to the control diets. In Trial 3, supplementing 10% single cell protein with a combination of conventional and non-conventional alternative protein sources showed better performance in terms of growth and body composition compared to other test diets. Survival was higher than 90% among the treatments, with no significant differences across all three trials. Feed efficiency and feed intake showed similar trends to growth performance for each trial. Although there were some significant differences in certain amino acids and fatty acids, the overall whole-body amino acid and fatty acid compositions did not show big differences among the groups. The study results suggest that up to 94% of fishmeal protein could be replaced by single cell protein in the diets of juvenile black sea bass.

A key outcome of the Phase 1 laboratory-scale feeding trials was the discovery that juvenile black sea bass can effectively utilize high levels of single-cell protein, Salicornia meal in combination with poultry by product meal, cottonseed meal and soybean meal in the diets replacing fishmeal without affecting fish growth. The results of the biochemical analysis of fish tissues of trial 1 and 2 clearly support the findings of the growth performance data indicating single cell protein and Salicornia meal could be used as alternatives to fishmeal to formulate the environmentally friendly diets for black sea bass. The best Eco-Aquafeed formulation with the combination of some alternative protein sources was recommended for the commercial scale farming of black sea bass. The findings, results, and techniques developed for feed formulation of black sea bass in Phase 1 lab-scale studies will positively contribute to reducing the use of fishmeal, an unsustainable commodity in aquafeed by incorporating non-conventional alternative protein sources such as single cell protein and Salicornia meal. While this project focuses on black sea bass, these outcomes could be used as a model for sustainable feed development for other species to support the expansion of marine finfish production throughout the U.S. 

Last Modified: 04/29/2025
Modified by: Md Shah Alam