Black Soldier Fly (Hermetia illucens) larvae oil in diet: Effects of growth, feed utilization; whole-body fatty acid and amino acid profile; immunology responses and Body Coloration of Goldfish Goldfish (Carassius auratus)
A 49-day feeding trial demonstrated that substituting 30% of traditional fish oil with Black Soldier Fly larvae oil in goldfish diets optimally enhances growth performance, feed efficiency, nutritional profiles, immune responses, and body coloration.
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In the world of ornamental fish keeping, the value of a creature is often measured by the brilliance of its scales and the vigor of its swim. Goldfish, with their flowing fins and shifting hues of orange and red, are a staple of this hobby, prized for their beauty and their ability to adapt to new environments. Behind this visual splendor lies a biological reality: the fish are only as healthy and colorful as the food they eat. For decades, the aquaculture industry has relied on fish oil as a primary source of fat in feed, a choice driven by its rich content of specific fatty acids that support growth and immune function. However, as global supplies of fish oil become scarcer and more expensive, scientists have been searching for a sustainable alternative that can provide the same nutritional benefits without depleting marine resources. One promising candidate has emerged from the insect world: the oil derived from the larvae of the black soldier fly. This insect is known for its ability to convert organic waste into high-quality protein and fat, offering a potential lifeline for feed manufacturers looking to replace traditional marine ingredients.
A team of researchers at Diponegoro University in Indonesia set out to test whether this insect oil could truly serve as a substitute for fish oil in the diet of goldfish. They were not just looking for a feed that kept the fish alive; they wanted to know if it could make them grow faster, utilize their food more efficiently, and perhaps even enhance the very colors that make them so desirable to keepers. To find the answer, they designed a controlled experiment involving a group of goldfish, each starting with an average weight of about 8.7 grams. The fish were divided into groups and fed diets where fish oil was gradually replaced by black soldier fly oil in increasing amounts, ranging from zero percent up to thirty percent. Over a period of forty-nine days, the researchers monitored every aspect of the fish's development, from how much they ate and how much they weighed at the end, to the chemical makeup of their bodies and the state of their immune systems.
The results of this forty-nine-day trial pointed clearly toward a single, optimal solution. The group of fish that received a diet with thirty percent of their fish oil replaced by black soldier fly oil outperformed all the others. These fish grew the most, gaining an average of over 61 grams by the end of the study, and they did so with the highest efficiency. They converted the food they ate into body mass better than any other group, requiring less feed to produce the same amount of growth. This improvement was not just a matter of size; the fish in this group also showed the best overall health markers. Their blood contained higher levels of red blood cells and white blood cells, suggesting a robust immune system capable of fighting off disease. The researchers found that the specific fatty acids and amino acids present in the black soldier fly oil were being absorbed and stored in the fish's bodies, effectively replacing the nutrients that would have come from the traditional fish oil.
Beyond the numbers of growth and survival, the study looked at the aesthetic qualities that define an ornamental fish. The researchers used a precise method to measure the color of the goldfish, analyzing the hue, brightness, and saturation of their skin. The fish fed the thirty percent black soldier fly oil diet displayed the most vibrant and aesthetically pleasing coloration. Their scales took on a deep, rich "Tiger Orange" with bright "Daffodil Yellow" highlights, a combination that is highly prized in the ornamental trade. This was a marked improvement over the control group, which ate a diet with no black soldier fly oil and displayed a duller, more yellowish tone. The study also examined the microscopic cells in the fish skin responsible for color, known as chromatophores. While the highest inclusion rate of the oil did not result in the highest number of these pigment cells, the overall visual effect was superior, indicating that the oil supported the quality and distribution of the color rather than just the quantity of pigment cells.
The findings suggest that black soldier fly oil is not merely a viable substitute for fish oil but can actually enhance the performance of goldfish when used at the right level. The thirty percent replacement rate proved to be the sweet spot, balancing the need for sustainable ingredients with the biological requirements of the fish. The oil provided a rich source of energy and essential nutrients that allowed the fish to grow faster and stay healthier, all while maintaining the vivid colors that make them so special. This research offers a concrete path forward for the aquaculture industry, demonstrating that insect-based ingredients can support the growth and beauty of ornamental fish without relying on dwindling marine resources. For the goldfish, the change in diet meant a healthier life and a more brilliant appearance, proving that the future of fish farming might just be flying.
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