Many carnivorous and omnivorous fish species exhibit reduced feed intake when the diets contain high levels of YM meal. This phenomenon is mainly attributed to the presence of chitin, a structural polysaccharide in the insect exoskeleton, which may not be efficiently degraded by fish lacking endogenous chitinases. Normally, chitin content in YM significantly increases as the larval stage progresses (Yu et al., 2021). In addition, high rigidness of chitin structure in YM or YM meal can result in poor palatability and deter feeding behaviors. Although chitinase-based treatment can effectively enhance the absorption and utilization of YM in aquaculture, the enzymatic hydrolysis demands strict operational conditions and the cost of enzyme preparation is high, limiting the practical application of this technical approach. Therefore, due to the presence of chitin structure, YM could not be digested efficiently by fish, thus leading to reduced nutrient absorption and suboptimal fish growth.

Compared with fishmeal offering a near-ideal balance of essential amino acids for aquaculture, YM meal is relatively deficient in some essential amino acids (EAA), including histidine, methionine, isoleucine, and tryptophan (Zhang et al., 2022). In the study of Yuan et al. (2022), with the substitution ratio of YM meal increased from 0 to 100%, histidine content in the large yellow croaker's diet significantly dropped from 1.26% to 0.62% (Yuan et al., 2022). In addition, YM lacks long-chain omega-3 polyunsaturated fatty acids (PUFA), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which play a key role in meat quality, immune function, and overall health of aquatic animals. It was observed that w-3/w-6 PUFA ratio of fish diet decreased remarkably from 0.65 to 0.25 as fish meal was completely replaced by YM meal (Yuan et al., 2022). Consequently, diets based solely on YM protein or lipid may fail to meet the nutrient requirements of aquatic animals, resulting in low substitution level of YM for fishmeal in aquafeed.

Safety risks caused by the contaminant accumulation pose serious regulatory and health concerns. YM grown on agricultural by-products or wastes can be regarded as bio-accumulators of heavy metals (e.g., cadmium, lead, arsenic) and mycotoxins (e.g., aflatoxin, deoxynivalenol) (Guo et al., 2023; Tang et al., 2024). Heavy metals in YM primarily begin with the bio-accumulation of these metals from soil by crops, while mycotoxins are mainly produced due to the high-humidity environment, which promotes fungal proliferation, in YM farming (Johnsen et al., 2021; Noyens et al., 2023). Bio-accumulation of these contaminants not only reduces meat quality of aquatic animals, but also threatens human's health through food chain (Anandkumar et al., 2020). Unlike conventional feed ingredients subject to stringent quality regulation, small-scale YM farming often lacks standardized management, strict traceability and complete certification systems. As a result, the use of YM in aquafeeds may introduce unacceptable food safety hazards.

Advances in functional genomics and gene editing now make it feasible to develop Tenebrio molitor strains with targeted characteristics, such as low chitin content and EPA/DHA enrichment. Firstly, fundamental research has fully revealed the formation process and regulatory mechanism of chitin structure in YM. A couple of essential enzymes (e.g., chitin synthetase B, trehalase, fructose-6-phosphate aminotransferase, etc.) and their regulatory genes have been identified (Chen et al., 2018). Theoretically, knockdown of the essential regulatory genes would block the formation of chitin structures in YM. In fact, this method has been successfully adopted in other insect species to regulate metabolic pathways of chitin (Yang et al., 2024). Secondly, EPA/DHA biosynthesis from the essential precursor α-linolenic acid involves a series of desaturation and elongation reactions. Specific enzymes, such as desaturase and elongase, and relevant genes for EPA/DHA biosynthesis have been fully studied. Since α-linolenic acid is enriched in the lipid of YM, it might be technically possible to redirect the metabolism toward EPA/DHA synthesis through introducing algal or fungal desaturase/elongase genes. Up to now, gene editing techniques have been successfully adopted to change certain traits of many insect species, such as silkworms, mosquitoes, and moths (Lim, 2025).

The impacts of gene editing on YM's metabolism are comprehensive and wide-ranging, yet there has been no in-depth assessment of these effects so far. For instance, would a reduction in chitin content affect the survival rate of YM? Could the accumulation of EPA/DHA interfere with the metabolism of other fatty acids? Before the industrial-scale application of gene editing in YM breeding, these scientific questions must be thoroughly investigated. In addition, due to the ethical hurdles, in the field of feed and food production, gene editing technology applications are strictly regulated by the government. In future research, a comprehensive assessment should be carried out on the safety of gene-edited YM, including aspects such as food safety and environmental safety. Particularly, with the technological improvement and cost reduction, gene-editing may become practically feasible, promoting the industrial upgrading of YM farming.

Comparison of previous studies demonstrated that under different feeding conditions, EEA and PUFA profiles of YM vary greatly (Zhang et al., 2022; Elahi et al., 2020). In addition to the metabolic mechanisms of YM, this phenomenon is attributed to the deficiency of specific nutrients in insect feed. Hence, through providing nutrient-enriched insect feed, nutritional composition of YM may be improved.

Following this approach, recent research has made a few attempts and achieved positive results. For example, inclusion of beer yeast in the insect diet resulted in the decrease of w-6/w-3 ratio in fatty acid composition of YM (Dreassi et al., 2017). In the study of Bordiean et al. (2022), w-6/w-3 ratio dropped from 20.55 to 17.11, 11.44 and 1.71, respectively, when wheat bran was partially replaced by rapeseed meal, rapeseed cake, and flax cake (Bordiean et al., 2022). In addition, YM fed diet with wheat bran (50%), oats (45%), and brewer's yeast (5%) contained significant higher concentrations of all eighteen amino acids (e.g., lysine, histidine, methionine, threonine, isoleucine, arginine, and tryptophan etc.) than YM fed maize stover (Stull et al., 2019). Supplementation of synthetic lysine also enhanced protein and amino acid deposition in YM (Fondevila et al., 2025). According to the aforementioned results, the concept of improving nutritional composition of YM by providing nutrient-enriched insect diet is practically feasible although it has not been widely adopted in the industry.

Aiming at producing YM with high nutritional value as fishmeal alternative, researchers can carry out their work from the following aspects. Firstly, specific methods to add EPA-enriched or DHA-enriched microorganisms, such as microalgae, cyanobacteria, and fungi, into insect feed could be developed. For example, to more efficiently increase the w-3 PUFA content in YM by adding microorganisms mentioned above, should the microorganisms be directly added to the insect feed or co-fermented with the feed ingredients? Secondly, specific effects of amino acid supplementation in insect diet on the growth performance and nutritional profile of YM should be fully studied. For instance, will the addition of synthetic amino acids have antagonistic effects with other nutritional fortifiers in insect feed? What impacts will the addition of specific amino acids have on YM's metabolism at the genetic and cellular levels? and so on. The basic research can provide theoretical support for optimizing feed formulations to increase EAA content in YM. Compared to genetic breeding, feed formulas optimization has a much lower technical barrier and can be more widely adopted to enhance the nutritional value of YM.

Instead of relying solely on thermal drying and mechanical milling, innovative methods such as enzymatic hydrolysis, solid-state fermentation, or mild extrusion could be employed. Firstly, enzymes like chitinase or protease can break down chitin-protein complexes, increasing the digestibility of YM nutrient. Secondly, solid-state fermentation using microorganisms with the ability of decomposing chitin-protein complexes and other compounds of YM is also applicable. Thirdly, mild extrusion could physically damage the chitin structure of YM without degrading nutritional components. The aforementioned technologies were extensively validated at the laboratory scale, but their energy consumption, investment requirement, and carbon footprint have been rarely studied. Therefore, current laboratory research on YM pretreatment remains insufficient to directly guide industrial practices.

YM farming sector must adopt rigorous quality assurance frameworks. Mandatory standards for YM production should include prohibition of high-risk feedstock, maximum permissible levels of heavy metals and mycotoxins in final YM products, Good Manufacturing Practices (GMP) for hygiene and pest control, and third-party certification for traceability. Only through such standardization can YM products gain the trust of feed manufacturers and aquaculture producers. Indeed, due to inadequate management systems, many developing countries are unable to implement rigorous oversight of the agriculture, aquaculture and feed industries. This limitation has consequently restricted the global market distribution of YM products from these regions. On the path to utilizing YM as a substitute for fishmeal, efforts must focus not only on technological innovation, but also on further improvement of regulatory frameworks.