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ABSTRACT

Feed constitutes over 50% of the total operational cost of aquaculture, which is mainly on account of the use of high protein sources. The high cost of fish meal and soybean meals demands the alternative protein source ingredient for aquafeed. Henceforth, insects like yellow mealworms (Tenebrio molitor) have brought researchers` attention due to their great nutritional profile and participation in a circular economy. Black soldier fly is primarily used in insect-based feeds; however, recent researches have come up with a considerable extent of using defatted mealworm in aquafeed. Substantial feeding trials have revealed its promising application beneficial in protein replacement and may have a vital role as a functional ingredient that boosts immunostimulatory effects in fish.

Keywords: Aquafeed, Fish Meal, Mealworm, Protein Source Ingredient

The Possibility of fish meal Replacement with mealworm

Based on the evidence published to date, there have been several studies of feeding trials performed on many species such as rainbow trout, Nile tilapia, European sea bass, gilthead sea bream, black spot sea bream, and olive flounder. Most of the reports suggested a diet with 25% to 70% replacement of fish meal with dried yellow mealworm larvae resulted in similar growth performance. Meanwhile, it has been found that the inclusion levels of mealworms in aquafeed depend on many factors, such as feeding habits, fish size and developmental stage. Moreover, predatory species probably cannot accept high yellow mealworm levels. Another limiting factor is the processing of mealworm due to high-fat levels, which could also affect the acceptability of fish. It has been reported that the high lipid content of mealworms reduces the availability of crude protein and lowers the extrusion quality during aquafeed processing. Thus, defatted T. molitor could be highly recommended to avoid aquafeed degradation and unstable pelleting for aquafeed (Rema et al., 2019).

Effect of mealworm on performance of fish

                The mealworms have an excellent nutritional component such as a relatively high amount of crude protein and crude fat, which could enhance the growth and nutrient utilization of fish. However, the amelioration of the potency to use nutrients by fish species may also be due to the presence of chitinous materials. In support of this, Ng et al. (2001) has noted the possibility of declination in growth performance and protein indices due to the higher inclusion of mealworms containing chitinaceous exoskeletons. The chitinous materials can modify the gastro-intestinal tract (GIT) microbiota, leading to better fish growth when included in relatively appropriate amounts.

Effect of mealworm on gut health and gut microbiota diversity

Digestive enzymes, especially protease, amylase, and lipase, play pivotal roles in the digestion and utilization of feed. A study on Nile tilapia reported the highest protease activity in the stomach and intestines in the fish fed with a mealworm-based diet with a 25% substitution of FM, followed by a diet with 50% of dietary FM substitution; and both groups exhibited higher digestive enzyme activities than those fed with FM-based diets (Sánchez-Muros et al. 2016). Likewise, intestinal protease and amylase activity was significantly enhanced in rainbow trout fed with a mealworm-based diet replaced by 60% FM (Melenchón et al., 2021).

                Moreover, Diets in which FM was replaced by insect meal from mealworms have led to changes in the diversity and abundance of fish gut bacteria; previous studies indicate that chitin, a major structural component of the insect cuticles, is a potential modulator of fish gut microbiota, as it acts as a substrate for chitinase producing bacteria that are not commonly found in the fish gut. Supplementation of chitin in the diet of Atlantic salmon (Salmo salar) modified the composition and structure of intestinal microbiota, with over a hundred autochthonous bacterial strains identified (Askarian et al., 2012). Generally, it was found that the increased richness and diversity of gut microbial communities are considered positive and desired features because they are usually associated with a healthy status of the host.

Effect of mealworm-based diet on immunity

The immunological responses, antioxidative capacity, and tolerance of aquatic species against stressors are always attributed to the influence of nutrients on the physiological pathways correlated with the feed quality. Despite an increasing number of studies addressing the effect of different dietary inclusion levels of yellow mealworm on fish performance, only limited studies have evaluated the effect of mealworms on immunological and health status aspects in aquaculture. However, some preliminary studies have displayed immunological aspects regarding the yellow mealworm-based diet fed to some fish species, such as rainbow trout and sea bass (Henry et al., 2018), which could be due to chitin or due to the similarities of the exoskeleton of parasites and insects.

Conclusion

In conclusion, we could illustrate that mealworm is a reliable source of fish food. The high protein content of the mealworm and rich source of amino acids make the yellow mealworm as an emerging protein source in aquaculture. However, the high moisture content of the mealworms may cause storage and handling issues, which could be alleviated by drying. Moreover, the fact that this insect is easy to rear and maintain assigns scope for the research to stipulate the ease of production of yellow mealworm using waste, nutritional value and environmental impact. To promote the meal of yellow mealworm in the fish feed sector as a novel protein source, documentation on its nutritional and food safety aspects is necessary. Moreover, future research will provide comparative knowledge with other insect species regarding bioconversion efficiency and quality. Further investigations are needed to evaluate the effect of mealworm on immune parameters and disease resistance to understand better how this ingredient can influence the health of fish. As a result, we can propose more strategies for including mealworms in aquafeed for sustainability without lowering the performance and quality of aquatic organisms. From the Food safety point of view, the forthcoming investigations will address the acceptability of the mealworm meal and the risk of contamination by it in the diet of fish.

References

Askarian, F., Zhou, Z., Olsen, R. E., Sperstad, S., & Ringø, E. (2012). Culturable autochthonous gut bacteria in Atlantic salmon (Salmo salar L.) fed diets with or without chitin. Characterization by 16S rRNA gene sequencing, ability to produce enzymes and in vitro growth inhibition of four fish pathogens. Aquaculture, 326, 1-8.

Belghit, I., Liland, N. S., Gjesdal, P., Biancarosa, I., Menchetti, E., Li, Y., ... & Lock, E. J. (2019). Black soldier fly larvae meal can replace fish meal in diets of sea-water phase Atlantic salmon (Salmo salar). Aquaculture, 503, 609-619.

Henry, M. A., Gai, F., Enes, P., Peréz-Jiménez, A., & Gasco, L. (2018). Effect of partial dietary replacement of fishmeal by yellow mealworm (Tenebrio molitor) larvae meal on the innate immune response and intestinal antioxidant enzymes of rainbow trout (Oncorhynchus mykiss). Fish & shellfish immunology, 83, 308-313.

Melenchón, F., Larrán, A. M., De Mercado, E., Hidalgo, M. C., Cardenete, G., Barroso, F. G., ... & Tomás‐Almenar, C. (2021). Potential use of black soldier fly (Hermetia illucens) and mealworm (Tenebrio molitor) insectmeals in diets for rainbow trout (Oncorhynchus mykiss). Aquaculture Nutrition, 27(2), 491-505.

Ng, W. K., Liew, F. L., Ang, L. P., & Wong, K. W. (2001). Potential of mealworm (Tenebrio molitor) as an alternative protein source in practical diets for African catfish, Clarias gariepinus. Aquaculture Research, 32, 273-280.

Ramos-Elorduy, J., González, E. A., Hernández, A. R., & Pino, J. M. (2002). Use of Tenebrio molitor (Coleoptera: Tenebrionidae) to recycle organic wastes and as feed for broiler chickens. Journal of economic entomology, 95(1), 214-220.

Ravzanaadii, N., Kim, S. H., Choi, W. H., Hong, S. J., & Kim, N. J. (2012). Nutritional value of mealworm, Tenebrio molitor as food source. International Journal of Industrial Entomology, 25(1), 93-98.

Rema, P., Saravanan, S., Armenjon, B., Motte, C., & Dias, J. (2019). Graded incorporation of defatted yellow mealworm (Tenebrio molitor) in rainbow trout (Oncorhynchus mykiss) diet improves growth performance and nutrient retention. Animals, 9(4), 187.

Sánchez‐Muros, M., De Haro, C., Sanz, A., Trenzado, C. E., Villareces, S., & Barroso, F. G. (2016). Nutritional evaluation of Tenebrio molitor meal as fishmeal substitute for tilapia (Oreochromis niloticus) diet. Aquaculture Nutrition, 22(5), 943-955.

 

Van Huis, A., & Oonincx, D. G. (2017). The environmental sustainability of insects as food and feed. A review. Agronomy for Sustainable Development, 37(5), 1-14.

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