UNCW researchers have a novel use for an ecological troublemaker.
Research Need
Aquaculture has emerged as a promising way to meet the growing demand for seafood while reducing pressure on wild populations. However, farmed fish diets, like those of household pets, rely heavily on fish meal and fish oil from wild-caught species like menhaden.
Not only are menhaden a valuable fishery, but they also play a key role as prey for many important gamefish, which places this species at the center of growing conservation and management concerns. As demand for fish meal outpaces supply, the search for sustainable protein alternatives in aquaculture diets is crucial.
In North Carolina, scientists are exploring an unexpected solution: the pleated sea squirt. In addition to disrupting local ecosystems by taking resources from other species, sea squirts can foul docks, boat hulls, and shellfish aquaculture operations.
But what if sea quirts could become an asset?
What did they study?
Researchers at UNC-Wilmington tested whether the pleated sea squirt can replace menhaden as a protein source in the diets of juvenile black sea bass. The university’s pilot-scale commercial aquaculture system provides a unique opportunity to research innovative ideas like this, often with student involvement.
UNCW’s team collected sea squirts from two locations where the species tends to grow in large numbers: an oyster farm in Masonboro Sound and under floating docks in Wrightsville Beach. After collecting sea squirts, the team freeze-dried and ground them into a fine meal.
To test the sea squirt’s effectiveness as fish food, the team fed juvenile black sea bass one of six different diets over 55 days.
The control diet, representing typical fish farming meal, used menhaden fish as the main protein source, making up 30% of the total diet. In the five test diets, researchers gradually replaced 8.3% to 41.6% of the fish meal with sea squirt meal. To maintain consistent nutrition, researchers adjusted other ingredients so that all diets contained the same overall protein and fat levels.
The team monitored the fish’s survival and growth rates, as well as how fish processed the food. At the end of the study, the team also analyzed the fish’s body composition and fatty acid levels, checked the nutritional makeup of each diet, and tested the sea squirt meal for metal content.
What did they find?
Sea squirt meal successfully replaced 41.6% — the highest level tested — of menhaden fish meal in the diet of juvenile black sea bass without negatively affecting their survival, growth, or overall health. Survival across all diets was high at 87% to 96%.
Fish that ate more sea squirt meal tended to grow larger and gain weight faster, with a body weight gain of 228% in the high replacement diet, compared to 157% in the control diet. While there were small differences in certain fatty acids, the overall levels of important omega-3s stayed consistent, especially when fish oil was added to the sea squirt-based meals.
What else did they find?
One limitation to using sea squirt meal in fish feed is the high mineral content, which can affect nutrient absorption by fish. However, researchers found that black sea bass maintained the same mineral levels despite consuming high-mineral sea squirt diets.
Another potential limitation is heavy metal accumulation in sea squirts, which, in turn, could accumulate in fish and impact human consumers. When researchers compared the heavy metal content of sea squirts from this study with past studies, they found that concentrations varied significantly depending on the collection site, highlighting the need for site-specific studies to determine safe levels for use in aquaculture feed.
So what?
The use of sea squirts in aquaculture feed could help reduce reliance on expensive and unsustainable fish meal, while offering comparable benefits to survival and growth in juvenile black sea bass. More research will determine optimal levels of sea squirts in feed, as well as its digestibility, potential for metal accumulation, associated impacts on human health, and economic feasibility.
Reading
Delmaine, A. D., Watanabe, W. O., Carroll, P. M., & Alam, M. S. (2024). Use of tunicate meal (pleated sea squirt Styela plicata) protein as a partial replacement of menhaden fish meal protein in the diet of juvenile Black Sea Bass. North American Journal of Aquaculture, 86(3), 295–312. /10.1002/naaq.10334
This study was funded in part by the UNCW Center for Support of Undergraduate Research and Fellowships.
Lead photo by Kevin Bryant/inaturalist via CC BY-NC-ND 2.0.
The text from Hook, Line & Science is available to reprint and republish at no cost with this attribution: Hook, Line & Science, courtesy of Scott Baker and Sara Mirabilio, North Carolina Sea Grant.
- Categories:
