On the west coast of the United States, there is an emerging aquaculture sector of small-scale farmers ranching wild capture urchins for the uni market. This supports the harvest of overabundant urchins and the regrowth and ecosystem health of kelp forests, their primary preferred food source. Efforts are underway to develop an open-source feed formulation that promotes efficient and high-quality uni production.
One of the most important factors impacting high versus low grade uni is color. Color is determined by the type and quantity of color pigments, carotenoids, accumulated in the uni through absorption from the diet or synthesis. This study examined the effects of different feed processing techniques on dietary carotenoid content and uni growth, color (L*A*B scores), and texture. Four treatment diets were tested: extruded diet + beta carotene, cold-pelleted diet + beta carotene, extruded diet + beta carotene top coated, and extruded diet + beta carotene/lutein/zeaxanthin top coated. Eight carotenoids were measured in samples before and after feed processing, including beta carotene, echinenone, lutein, zeaxanthin, astaxanthin, canthaxanthin, cryptoxanthin, and violaxanthin. Diets were fed to triplicate tanks of urchins with n=10-13 individuals per tank for 8-10 weeks.
The cold pelleted + beta carotene diet lead to a lower GSI, A (Figure 1), and B scores compared to the extruded diet + beta carotene. There was no change in hardness, springiness, gumminess, or chewiness between diets. The extruded diet + beta carotene exhibited 80% uni of visual A/A+ grade and A/A- taste. The extruded diet + beta carotene/lutein/zeaxanthin exhibited 86% uni of visual A/A+ grade and 100% uni of A/A- taste. The extruded diet + beta carotene top coated exhibited 50% uni of A/A+ grade and 100% uni of A/A- taste.
There was no evidence that extrusion degraded carotenoid content. These data suggest that extruded diets perform similarly or better than cold pelleted diets or extruded diets with carotenoids top coated. The time between feed production and use as well as the water stability of feed and dietary carotenoids are important considerations for production efficiency and product quality.