Reducing Fish Meal Dependency in Juvenile Yellowtail Diets Using Composite By-Product Protein Mixtures

Area of Science:

• Aquaculture Nutrition
• Sustainable Feed Development
• Marine Biology

Background:

• Fish meal (FM) is a primary protein source in aquaculture diets.
• Sustainable alternatives are needed to reduce reliance on FM.
• Shark by-products represent an underutilized resource.

Purpose of the Study:

• To evaluate composite protein mixtures from shark by-products as partial FM replacements in yellowtail diets.
• To assess the impact of these replacements on growth, feed efficiency, and proximate composition.
• To determine the optimal replacement level without compromising fish health and nutritional value.

Main Methods:

• A 6-week feeding trial with juvenile yellowtail (Seriola quinqueradiata).
• Five diets were formulated: control (FM-based) and four test diets with 25% or 35% FM protein replaced by two different shark by-product mixtures (SSM and SMM).
• Growth performance, feed efficiency, survival, and whole-body proximate composition were analyzed.

Main Results:

• No significant differences in growth performance (weight gain, specific growth rate, survival) were observed among treatments.
• Feed efficiency was significantly higher in diets with 25% and 35% shark by-product meal (SS25, SS35) compared to the control.
• Whole-body proximate composition remained largely unaffected, though n-3 fatty acid levels decreased in some SMM diets.

Conclusions:

• Up to 35% of fish meal protein can be replaced by composite shark by-product mixtures in juvenile yellowtail diets.
• These by-product-based diets can maintain growth performance and improve feed efficiency.
• Shark by-products offer a promising sustainable ingredient for aquaculture feed formulations.