One of the main challenges in rainbow trout aquaculture is finding sustainable protein sources for fish feed. Fish meal has traditionally been used, but this puts pressure on wild fish populations, and climatic events like El Niño can lead to shortages of this input for aquaculture feeds.
Researchers from the US Fish and Wildlife Service and the University of Idaho conducted an in vivo trial to determine the apparent digestibility coefficients (ADC) of insect meals for rainbow trout, Oncorhynchus mykiss.
Why insects?
Fish meal has been a key ingredient in aquaculture feeds. However, concerns about overfishing and the environmental impact of fish meal production have driven the search for alternatives. Insects offer a promising solution:
- Natural diet: Insects are a natural part of the diet of many fish species, both freshwater and marine.
- Waste warriors: Insects have an impressive ability to convert waste into valuable nutrients. This efficiency makes them a more sustainable protein source compared to traditional fish meal production.
- High protein content: Insects have impressive protein levels, ranging from 34% to 74% dry matter, with some species reaching closer to 70%.
- Sustainable option: Insect farming offers a lower environmental footprint compared to traditional fish meal production.
Promising candidates
There is a diversity of insect species; however, not all have the potential to become feed ingredients for aquaculture diets. Various scientific studies have identified the following insect species with the highest potential:
- Yellow mealworms (Tenebrio molitor): These larvae have been widely studied and show promise due to their high protein content (47-60% DM) and lipids (31-43% DM), along with a favorable amino acid profile.
- House crickets (Acheta domesticus): Adult house crickets are packed with proteins (around 67% DM) and lipids (22% DM). While less explored in fish feeding, they have potential.
- Wax moth larvae Galleria mellonella: Although not as widely researched, wax moth larvae have a unique combination of proteins (around 31% DM) and high fat content (almost 48% DM).
The experiment
The researchers conducted an in vivo trial (i.e., within a live organism) to assess the digestibility of various insect meals for rainbow trout. The trout were fed diets containing:
- Herring fish meal (MFM): The traditional protein source (control group).
- House cricket meal (A and B): Two different options of cricket meal.
- Yellow mealworm meal: A protein-rich insect meal.
- Galleria mellonella meal: A high-fat insect meal (wax moth larvae).
The fish were monitored for two weeks, and then their waste was analyzed to determine how well they digested the different diets.
Promising results
- Cricket power: House crickets (A and B) and yellow mealworms showed promise as protein alternatives to fish meal. Their apparent digestibility coefficients (ADC) were comparable to MFM, indicating efficient nutrient absorption by trout.
- Wax moth potential: Galleria mellonella larvae meal stood out for its high digestibility, suggesting it could be a valuable source of lipids (fats) for fish feed.
- Delays in cricket B: Interestingly, house cricket B showed lower protein digestibility compared to others. Further research is needed to understand this variation.
Unlocking potential
While promising, there are some limitations to using insects in aquaculture feeds:
- Digestibility: Not all insect meals are equally digestible by fish, and experiments have been conducted with chitinase to improve the digestion of insect meals. The maximum amount of fish meal replaced by insects depends on the specific insect species. Some insects may require further processing to optimize digestibility.
- Knowledge gap: Compared to traditional fish meal, there is less information on the nutrient availability of different insect meals for fish.
Why insects are important
The study paves the way for insect-based protein sources in sustainable and environmentally friendly aquaculture. House crickets, yellow mealworms, and even wax moth larvae show potential to replace fish meal in rainbow trout diets. Further research can optimize these insect meals and explore their broader application in aquaculture.
While these initial findings are promising, more research is needed. Optimizing insect meal processing and understanding the long-term effects on fish health are crucial steps.
Contact
Wendy M Sealey
US Department of Agriculture, Agricultural Research Service, Bozeman Fish Technology Center, Bozeman, MT 59715, USA
Email: Wendy.Sealey@usda.gov
Reference (open access)
Owens, C. E., Powell, M. S., Gaylord, T. G., Conley, Z. B., & Sealey, W. M. Investigation of the suitability of 3 insect meals as protein sources for rainbow trout (Oncorhynchus mykiss). Journal of Economic Entomology. https://doi.org/10.1093/jee/toae037
