From Gut to Fillet: Comprehensive Effects of Tenebrio molitor in Fish Nutrition

Abstract

As aquaculture expands, there is a growing demand for sustainable and environmentally friendly feed ingredients that can replace conventional fish meal while maintaining high biological value and digestibility. The use of fishmeal has contributed to overfishing, making it an increasingly limited and unsustainable resource. Tenebrio molitor (TM) is emerging as a sustainable alternative to fishmeal (FM) in aquaculture diets, gaining attention due to its balanced protein composition profile and low environmental footprint. This review critically analyses data from the literature on the use of TM meal as a substitute for fish feed ingredient, focusing on its effects on growth performance, physiological status, and histological changes in the digestive and muscular systems. The influence on the physicochemical and sensory quality of fish meat is also evaluated. The discussion highlights both the benefits and possible adverse effects, such as intestinal inflammation or changes that may occur, depending on the replacement level. The paper presents recommendations and strategies to mitigate these effects, including the use of dietary supplements or partial replacement schemes. Overall, this paper emphasises the promising potential of TM as a sustainable alternative to FM in aquaculture feed, while highlighting the need for further research into the long-term effects, involved metabolic pathways, and standardisation of insect meal production. This review provides valuable insight into the physiological changes that may occur, particularly at high inclusion levels. As TM is utilized in both human nutrition and aquaculture diets, monitoring its physiological effects in fish is essential, since any alterations may have implications for human food safety.

1. Introduction

In order to meet the basic needs of the population, the global demand for protein, both for animal feed and for human consumption, is increasing. However, approximately 7.4% of the global population does not have access to even the minimum required amount of protein. Most of these people live in poor countries in sub-Saharan Africa or Latin America [1]. According to European Regulation (EU) No. 2017/893 [2], processed animal proteins (PAP) derived from seven insect species are approved as promising alternatives to fishmeal in aquaculture feed: the black soldier fly (Hermetia illucens), the housefly (Musca domestica), the yellow mealworm (Tenebrio molitor), the lesser mealworm (Alphitobius diaperinus), the house cricket (Acheta domesticus), the banded cricket (Gryllodes sigillatus) and the field cricket (Gryllus assimilis). According to Regulation (EU) No 999/2001 [3] these insects have been approved exclusively in aquaculture diets. Subsequently, Commission Regulation (EU) No 2021/1372 extended this authorisation to include poultry and pig diets [4]. Starting in 2021, the silkworm species (Bombyx mori) was also approved for use as PAP in aquaculture, poultry, and pig diets [5]. Four insect species have been approved for human consumption in accordance with Regulation (EU) 2015/2283 [6] and the relevant marketing regulations: dried mealworm larvae TM [7], Locusta migratoria [8], Acheta domesticus [9], and Alphitobius diaperinus [10]. Recently, on 20 January 2025, UV-treated TM powder was also authorised [9]. Insects represent a promising and sustainable solution for converting food losses and organic waste into valuable products for human and animal consumption. They serve as an environmentally friendly alternative to conventional protein sources, including both animal and plant-based proteins, and can be incorporated into food and feed [11,12]. Certain insect species, such as the black soldier fly (Hermetia illucens) and TM, not only provide protein but also enhance soil fertility by converting organic residues [13] and can aid in the biodegrading of plastic [14]. A recent study also states that mealworm feed substrate waste has high nutritional value and it can be used as fish feed [15]. TM is the most widely produced insect for food and feed globally, as it is easy to manage, requires little space and can consume a variety of agricultural residues [16,17,18]. It is probably the most widely used species for producing fish and poultry feed [19,20] and is also considered the most acceptable to consumers in Europe [21]. A recent study states that TM can be used for fattening lambs [22]. However, research has shown that insect protein alternatives can have adverse effects on the physiological status, metabolism and health of fish [23]. Unfortunately, different sources that are rich in protein still remain deficient in micronutrients or contain toxic substances that are harmful to fish health. Conversely, plant-based protein sources may disrupt the intestinal microflora and induce moderate to severe inflammation, depending on the quantity and species [24,25]. These effects are largely attributed to the presence of anti-nutritional factors (ANFs), including saponins [26,27], Kunitz and Bowman–Birk trypsin inhibitors [28], phytates, and indigestible starch [29]. The most promising protein alternative in this case is therefore insect meal. Of all the species approved by the European Commission, TM has a balanced protein profile and a higher digestibility coefficient than other species [30,31]. Studies have shown that replacing fishmeal with TM meal improves growth performance and feed conversion efficiency [30,32,33]. However, growth performance and digestibility begin to decline when FM is replaced almost entirely or completely [34]. This leads to liver inflammation and different histological changes in the liver and kidneys [35], as well as metabolic [36], intestinal [34], and meat composition changes [31,37]. These changes depend on the species, the percentage of replacement, the amount of chitin, the diet composition, and the alteration of the microbiome [30,31,32,35,38,39]. This study aims to evaluate the effects of replacing FM in various proportions and forms with the TM meal in the diet of different fish species. The study will analyse the impact on growth performance, physiological status, blood biomarkers, histological changes in the digestive tract and muscles, the physical and chemical composition of the meat, and the sensory profile. The study will also identify the optimal inclusion limits recommended for each species and strategies to mitigate the possible negative effects generated by the partial or total replacement of FM.

2. Materials and Methods

A systematic literature search was conducted in key academic, peer-reviewed databases, including Web of Science, Scopus, ScienceDirect, and Google Scholar. The search terms ‘Tenebrio molitor’, ‘fishmeal replacement’, ‘insect-based diets’, ‘blood biomarkers’, ‘fish fillet quality’, ‘chitin digestibility’, and ‘growth performance’ were used. The search was restricted to the following fields: Title, Abstract, and Author Keywords. Acceptance criteria included all articles published in English between 2004 and 2025, focusing on original research and reviews. Studies not directly related or published in non-peer-reviewed sources were excluded. Duplicate records were removed, and the remaining articles were screened first by title and abstract, followed by full-text review to ensure relevance and quality. This process ensured a comprehensive and systematic collection of the literature for subsequent analysis. All selected studies were evaluated for relevance to growth performance, physiological parameters, and feed utilization. Figures were created using BioRender (https://BioRender.com; accessed on 8 August 2025), Figure 1 [40] and Graphical abstract [41].

3. Growth Performance

The growth performance of fish fed diets with varying levels of FM or soybean meal (SBM) replacement by TM meal was compared across species and experimental conditions. Parameters such as initial and final body weight, specific growth rate (SGR%), feed conversion ratio (FCR), protein efficiency ratio (PER), and survival rates (SR%) were evaluated. However, these comparisons are limited by differences in fish species, experimental duration, diet composition, inclusion levels of TM meal, chitin content, culture period or photoperiod, and rearing conditions, which may influence growth responses. Despite these limitations, the analysis provides an overview of the potential effects of TM meal inclusion on fish growth performance and offers guidance on optimal inclusion or replacement levels of FM or SBM according to species.

According to Hossain et al. (2025) [35], replacing fish meal with defatted mealworm (DMW) at inclusion levels of 25%, 50%, 75%, and 100% in the diet of Oncorhynchus mykiss represents a viable alternative for fish feed. All experimental groups exhibited comparable growth performance and feed intake, along with good health status and SR% ranging from 86.9% to 96.9%.

In the large yellow croaker (Larimichthys crocea), replacing FM with TM meal supported good growth performance up to an inclusion level of 30%. Beyond this threshold, growth decreased significantly, and the FCR showed higher values. Across all tested groups (0%, 15%, 30%, 45%, 60%, 75%, and 100% TM), the SR% ranged from 84.67% to 94.67% [42].

When FM is replaced with full-fat mealworm (FFMW) in the diet of Acipenser stellatus, growth performance is enhanced up to an optimal inclusion level of 10%. At this level, fish exhibit the highest SGR% and the most efficient utilisation of dietary protein and energy. However, at higher inclusion levels (20% and 30% FFMW), growth performance begins to decline [43].

In Grass carp (Ctenopharyngodon idellus), final body weight, (SGR%), protein efficiency ratio (PER), and FCR reached their highest values when 25% of the SBM-based diet was replaced with TM meal. Beyond this level, all growth parameters began to decline, and FCR increased. SR% ranged from 86% to 90% [44].

According to Yang et al. (2025) [44], TM-based feed contains higher levels of essential amino acids (EAAs) isoleucine, leucine, lysine, methionine, threonine, and valine, as well as non-essential amino acids (NEAAs) alanine, glycine, and proline compared to SBM.

In the case of O. shiranus, replacing FM with 25%, 50%, and 75% FFMW did not affect growth performance. The group fed with 75% FFMW recorded the highest body weight and hepatosomatic index (HSI), possibly due to the higher crude fat (CF) content in the diet [45]. The optimal inclusion rate of FFMW in the diet of O. shiranus is 50–70% with the highest SR% of 78.33–76.67%.

In juvenile largemouth bass (Micropterus salmoides), feed restriction followed by refeeding with diets in which FM was completely replaced by TM meal was found to be detrimental to both growth performance and liver health [46].

Table 1. Optimal fish growth rate as determined by species and dietary inclusion level of TM meal.

Species and References	Fish Feeding Habits	Aquaculture System	Initial Weight	Culture Period/Photoperiod	Experimental Period Days	Types of Meal Used	Substitution of Fish Meal	Substitution of Vegetal Protein	Tenebrio molitor Inclusion
Stellate sturgeon Acipenser stellatus [43]	Carnivorous	flow-through	28.08 ± 0.13 g	12 h light/ 12 h dark	56	FFMW	-	-	10%
Rainbow Trout Oncorhynchus mykiss [35]	Carnivorous	flow-through	23 ± 0.4 g	12 h light/ 10 h dark	91	DMW	50–75%	-	20–30%
Rainbow trout Oncorhynchus mykiss [30]	Carnivorous	RAS	1.11 ± 0.01 g	natural conditions	56	TM	28%	-	-
European seabass Dicentrarchus labrax [32]	Carnivorous	RAS	21.1 ± 4.9 g	12 h light/ 12 h dark	49	FFMW	-	20%	-
Large yellow croaker (Larimichthys crocea) [42]	Carnivorous	marine floating net cages	189.18 ± 0.13 g	natural conditions	80	FFMW	45%	-	25.57%
Grass carp Ctenopharyngodon idellus [44]	Herbivorous	nylon net pond cages	20.57 ± 0.34 g	natural conditions	56	FFMW	-	25%	-
Nile tilapia (Oreochromis niloticus) [47]	Omnivorous	flow-through	60.00 ± 5.35 g	natural conditions	30	TM	-	15–60%	-
Nile tilapia (Oreochromis niloticus) [48]	Omnivorous	biofloc system	2.08 ± 0.19 g	not specified	42	TM	-	-	10%
Shire tilapia Oreochromis shiranus [45]	Omnivorous	concrete earthen ponds	15.02 ± 1.23 g	natural conditions	126	FFMW	50–75%	-	-
Largemouth Bass juvenile (Micropterus salmoides) [49]	Carnivorous	RAS	158.9 ± 1.7 g	12 h light/ 12 h dark	77	TM	19.52%	-	-
Blackspot sea bream (Pagellus bogaraveo) [50]	Omnivorous	flow-through	110.67–246.36 g	natural conditions	131	FFMW	25%	-	-
Rockfish (Sebastes schlegeli) [51]	Carnivorous	flow-through	3.11 ± 0.01 g	natural conditions	56	TM	32%	-	16%
Sea trout— (Salmo trutta) [52]	Carnivorous	flow-through	0.14 g	16 h light/ 8 h dark	60	TM	-	-	20%
Common carp (Cyprinus carpio) [53]	Omnivorous	RAS	97.54 g ± 51.0 g	not specified	21	DMW	50%	-	-

TM, Tenebrio molitor; DMW, defatted mealworm; FFMW, full-fat mealworm; RAS, recirculating aquaculture system.

presents the optimal growth rates of fish, as determined according to species and the dietary inclusion levels of TM meal.

Feed Digestibility

Several studies have shown that DMW is highly digestible for fish, particularly regarding essential amino acids, with digestibility values exceeding 90% [35]. However, when mealworm constitutes the only protein source, supplementation with cysteine and taurine is recommended due to their relatively low digestibility, reported at 79.30% and 72.34%, respectively [35].

It has been observed that with an increasing proportion of TM in the fish diet, there is a linear decrease in the digestive enzymes amylase and lipase [44], leading to reduced carbohydrate digestibility, decreased absorption of essential fatty acids [54], and lower uptake of fat-soluble vitamins. In Oreochromis shiranus, nutrient digestibility increased with the replacement of commercial feed with FFMW till 75% [45].

One component of TM that affects fish digestion is chitin, an important polysaccharide abundantly present in insect exoskeletons [55]. The chitin content of TM exhibits developmental stage-dependent variation, with levels measured at 4.60 ± 0.05% in larvae, 3.90 ± 0.05% in pupae, and 8.40 ± 0.05% in adults [56]. Chitin, a complex β-(1→4) polysaccharide, is poorly digestible due to its rigid structure; to be utilized, it must be hydrolyzed into N-acetylglucosamine, an absorbable monomer [55]. This reaction is catalyzed by chitinase, an enzyme that breaks chitin down into oligosaccharides or N-acetylglucosamine monomers, which can then be efficiently digested and absorbed by the organism. Some fish species that naturally consume chitin possess endogenous chitinase, enabling them to utilize dietary chitin more efficiently [57,58,59]. Although some fish species possess this chitinolytic enzyme, at high inclusion levels of TM, digestive efficiency is markedly reduced, resulting in incomplete chitin degradation and negatively impacting nutrient digestibility and assimilation [55,60].

Table 2. Effect of Chitin on fish species-specific digestive responses.

Species and References	Diet	Fish Feeding Habits	Aquaculture System/Period Days	Initial Weight g	Final Weight g	PER	SR%	Chitin Content %	Effect on Digestibility
Rainbow Trout Oncorhynchus mykiss [61]	FM	Carnivorous	flow-through 90 days	116.5 ± 0.40	313.8 ± 2.51	1.69	86.7	-	ADC of CP 92.2%
	25% TM			115.2 ± 0.40	316.6 ± 2.51	2.06	96.7	-	ADC of CP 91.5%
	50% TM			115.9 ± 0.40	308.2 ± 2.51	2.04	97.5	-	↓ ADC of CP 90.1%
Rainbow Trout Oncorhynchus mykiss [62]	30% TM	Carnivorous	RAS 14 days	370 ± 23	-	-	-	-	↑ good ↑ ADC of CP. No differences in the ADC
Nile tilapia (Oreochromis niloticus) [63]	20% TM	Omnivorous	RAS 15 days	3.0 ± 0.2	-	-	-	3.87	↑ good ↑ ADC of moisture 95.8; ↑ ADC of CP 85.4%
Meagre (Argyrosomus regius) [60]	FM	Carnivorous	RAS with flow of seawater 48 days	18.0 ± 0.02	80.5 ± 8.9	2.49	0	0	↑ ADC of CP 94.1%
	10% TM				66.1 ± 4.2	2.22	0	0.74	ADC of CP 92.9%
	20% TM				53.2 ± 3.1	2.07	0	0.97	ADC of CP 92.5%
	30% TM				40.0 ± 1.0	1.67	3.7	1.47	↓ ADC of CP 91.9%; ↓ ADC of AA,
African Catfish Hybrids (Clarias gariepinus × Heterobranchus longifilis) [64]	30% TM	Omnivorous	RAS 18 days	217.4 ± 9.5	346 ± 35.8	-	-	5.81	↓ ADC of CP 72.07% ↓ ADC of CF 81.24% ↓ ADC of AA
Gilthead sea bream (Sparus aurata) [65]	FM	mainly Carnivorous	RAS 163 days	105.2 ± 0.17	239.6	1.74	-	1.15–2.31	ADC of CP 89.97% ADC of CF 91.12%
	20% TM				294.6	2.26	-		ADC of CP 87.26% ADC of CF 89.93%
	50% TM				238.9	1.79	-		↓ ADC of CF 82.39%; ↓ ADC of CP 79.19%

TM, Tenebrio molitor; ADC, apparent digestibility coefficients; CP, crude protein; PER, protein efficiency ratio; SR%, Survival rate; AA, Amino acids; CF, Crude fat.

details the species-specific digestive responses of fish to dietary chitin.

Table 3. Mealworm flour composition and the species-specific growth performance depending on the level of FM or SBM replacement.

Species and References	Fish Feeding Habits	Aquaculture System/Period Days	Culture Period/Photoperiod	Types of Meal Used	Composition of Mealworm %					FM Substitution/Inclusion TM	Initial Weight (g)	Final Weight (g)	SGR %/Day	FCR	PER	SR%
					Moisture	Crude Protein	Crude Fat	Ash	Energy (MJ/Kg)
Rainbow Trout Oncorhynchus mykiss [35]	Carnivorous	flow-through 91 days	12 h light/ 10 h dark	FM	4.94	47.02	16.81	5.48	22.23	0%	23.1	264.4	2.68	0.72	3.00	94.4
				DMW	4.78	47.11	16.01	5.56	22.21	25%	23.5	242.4	2.56	0.76	2.80	86.9
					4.83	46.48	17.42	5.65	22.35	50%	23.4	268.3	2.68	0.76	2.82	91.9
					5.07	47.42	16.02	5.71	22.27	75%	23.0	264.6	2.68	0.79	2.68	87.5
					4.88	47.10	16.06	5.71	22.67	100%	23.2	264.9	2.68	0.77	2.75	96.9
Stellate sturgeon Acipenser stellatus [43]	Carnivorous	flow-through 56 days	12 h light/ 12 h dark	FM	6.25	45.27	25.15	8.57	19.31	0%	28.20 ± 3.68	71.40 ± 1.90	1.76	1.98	1.98	100
				FFMW	6.13		3.15	7.75	19.59	10%	27.90 ± 2.12	77.25 ± 2.04	1.87	2.02	2.82	100
					6.19		15.62	8.16	19.48	20%	28.10 ± 2.97	63.12 ± 4.32	1.52	3.45	1.81	90
					6.25		15.25	8.57	19.31	30%	28.10 ± 0.42	62.49 ± 2.21	1.50	3.76	1.78	85
European sea bass Dicentrarchus labrax [32]	Carnivorous	RAS 49 days	12 h light/ 12 h dark	FM	8.35	46.7	21.8	5.52	-	0%	21.16 ± 4.89	48.45 ± 8.39	-	1.11	-	-
				FFMW	9.07	47.0	21.1	5.98	-	5%	21.61 ± 4.64	47.89 ± 8.61	-	1.08	-	-
					9.49	47.2	21.5	6.16	-	10%	21.23 ± 4.90	46.61 ± 8.35	-	1.11	-	-
Grass carp Ctenopharyngodon idellus [44]	Herbivorous	nylon net pond cages 56 days	natural conditions	SBM	-	30.56	5.64	10.29	-	0%	20.73 ± 0.534	60.11 ± 0.669	0.94	1.71	1.98	87.33
				FFMW	-	30.62	5.67	10.07	-	25%	20.27 ± 0.500	64.16 ± 0.557	0.96	1.62	2.29	90
					-	30.65	5.69	10.04	-	50%	20.24 ± 0.334	58.56 ± 1.011	0.87	1.90	2.15	88.67
					-	30.67	5.61	10.15	-	75%	20.60 ± 0.193	58.20 ± 0.367	0.92	1.90	2.04	90.00
					-	30.73	5.66	10.25	-	100%	21.02 ± 0.070	55.77 ± 0.670	0.89	1.80	1.83	86.00
Shire tilapia Oreochromis shiranus [45]	Omnivorous	concrete earthen ponds 126 days	natural conditions	FM	-	30.45	8.34	7.14	22.03	0%	15.19 ± 0.24	51.47 ± 1.97	3.18	2.93	-	70.56
				FFMW	-	30.62	8.55	5.73	24.30	25%	15.06 ± 0.34	49.63 ± 1.68	3.13	2.89	-	73.33
				FFMW	-	29.95	9.18	5.88	22.42	50%	15.01 ± 0.55	48.62 ± 1.95	3.11	2.67	-	78.33
				FFMW	-	30.98	9.41	5.47	23.99	75%	14.95 ± 0.23	52.86 ± 0.45	3.22	2.62	-	76.67
Blackspot sea bream (Pagellus bogaraveo) [50]	Omnivorous	flow-through 131 days	natural conditions	FM	7.14	45.80	19.71	10.09	-	0%	171.25	223.69	0.21	5.32	-	-
				FFMW	7.35	45.90	19.82	8.77	-	25%	171.32	218.81	0.20	5.87	-	-
				FFMW	7.03	45.93	20.80	7.42	-	50%	174.15	218.20	0.19	5.52	-	-
Beluga (Huso huso) [66]	Carnivorous	RAS 56 days	not specified	FM	-	40.26	21.55	10.64	19.01	0%	121.66 ± 2.51	391.86 ± 24.53	2.07	1.60	-	100
				TM	-	40.41	21.27	10.93	18.92	20%	121.66 ± 3.78	451.80 ± 23.40	2.34	1.30	-	100
				TM	-	41.27	20.86	9.83	19.03	40%	105.33 ± 10.15	424.53 ± 18.41	2.5	1.34	-	100
				TM	-	40.11	21.30	9.11	19.10	60%	105.33 ± 13.32	416.80 ± 28.23	2.47	1.38	-	100
				TM	-	40.62	20.23	8.65	18.94	80%	110.33 ± 8.57	409.8 ± 16.25	2.37	1.42	-	100
				TM	-	40.26	20.28	8.25	18.96	100%	116.1 ± 6.2	415.26 ± 11.37	2.27	1.43	-	100
Nile tilapia (Oreochromis niloticus) [48] juveniles reared in biofloc system	Omnivorous	biofloc system 42 days	not specified	FM	-	30.94	12.08	8.81	-	0%	2.07	8.36	3.32	1.44	-	96.67
				TM	-	34.13	11.53	8.76	-	5%	2.08	9.41	3.60	1.34	-	83.33
				TM	-	33.01	11.99	8.31	-	10%	2.1	9.44	3.57	1.28	-	90.00
				TM	-	30.95	13.58	7.78	-	15%	2.07	9.44	3.61	1.32	-	73.33
				TM	-	33.65	15.35	8.74	-	20%	2.1	10.37	3.80	1.21	-	53.33
Atlantic Salmon (Salmo salar) [67]	Carnivorous	RAS 84 days	12 h light/ 12 h dark	FM	4.00	43.8	22.5	5.28	-	0%	38.5 ± 0.1	182.8 ± 5.5	1.53	1.23	2.64	100
				DMW	3.50	43.7	22.5	5.02	-	50%	38.7 ± 0.1	179.0 ± 2.6	1.50	1.20	2.54	100
				DMW	3.50	43.6	22.5	5.58	-	100%	38.4 ± 0.1	191.4 ± 5.5	1.50	1.25	2.69	98.8
				FFMW	3.00	43.8	22.7	4.86	-	50%	38.4 ± 0.2	191.5 ± 3.6	1.60	1.23	2.57	100
Large Yellow Croakers (Larimichthys crocea) [68]	Carnivorous	floating sea cages 56 days	natural conditions	FM	1.98	47.98	8.25	11.12	-	0%	11.76 ± 0.06	26.59 ± 0.27	2.12	0.72	1.50	84.22
				DMW	1.51	48.30	8.63	10.70	-	15%	11.78 ± 0.06	26.18 ± 0.31	2.00	0.70	1.44	89.33
				DMW	1.41	48.00	8.76	10.85	-	30%	11.84 ± 0.02	24.89 ± 0.15	2.24	0.57	1.20	76.33
				DMW	1.15	48.10	8.79	10.50	-	45%	11.84 ± 0.04	21.31 ± 1.02	2.36	0.47	0.98	76.67

FM, fish meal; DMW, defatted mealworm; FFMW, full-fat mealworm; SBM, Soybean meal; TM, Tenebrio molitor; SGR, specific growth rate % day; FCR, feed conversion ratio; PER, protein efficiency ratio; SR, survival rate; RAS, recirculating aquaculture system.

details the mealworm flour composition and the species-specific growth performance depending on the level of FM or SBM replacement.

4. Fish Meat Composition

The inclusion of TM in fish feed affects certain proximate composition components (water, fat, protein) depending on the level of replacement, without compromising meat quality. Moisture content in the fillet is higher in fish fed with FM compared to those fed exclusively with DMW or FFMW. As the proportion of DMW or FFMW in the diet increases, the fat content in the fillet rises linearly [35]. In some studies, crude protein did not show significant variation between groups [35]; however, in a few studies, a decreasing trend in crude protein was observed with increasing FFMW content in the diet [43]. With an increase to 10% FFMW, it was observed that the fish had more perivisceral fat [32]. Studies have shown that diets containing TM modify the lipid profile by increasing total phospholipids and reducing triglycerides and sterols in the muscle, which may suggest more efficient fat utilisation [32]. Replacing plant proteins with 20% TM in the feed improved growth performance and meat quality by reducing neutral lipids (triglycerides and sterols) while maintaining n-3 PUFA and DHA levels in the tissue [32].

The physicochemical composition of fish fillet, according to species and the level of TM replacement, is presented in

Table 4. Physicochemical composition of fish fillet related to species and level of TM replacement.

Species and References	Diet	Fish Feeding Habits	Aquaculture System/Period Days	Culture Period/Photoperiod	Moisture%	CP%	CF%	Ash
Stellate sturgeon Acipenser stellatus [43]	FM	Carnivorous	flow-through 56 days	12 h light/ 12 h dark	71.63 ± 1.78	15.12 ± 1.63	11.84 ± 0.47	2.42 ± 0.14
	10% FFMW				69.73 ± 1.25	15.14 ± 0.46	11.88 ± 0.58	2.28 ± 0.27
	20% FFMW				67.92 ± 1.89	14.82 ± 0.62	12.15 ± 0.44	1.97 ± 0.14
	30% FFMW				68.12 ± 1.68	14.75 ± 1.12	14.52 ± 0.54	1.92 ± 0.44
Rainbow Trout Oncorhynchus mykiss [35]	FM	Carnivorous	flow-through 91 days	12 h light/ 10 h dark	73.37	20.33	5.16	2.07
	25% DMW				73.66	20.54	4.83	2.09
	50% DMW				73.35	20.55	5.12	2.21
	75% DMW				72.57	20.42	5.72	2.00
	100% DMW				73.20	20.58	5.23	2.17
Grass carp Ctenopharyngodon idellus [44]	SBM	Herbivorous	nylon net pond cages 56 days	natural conditions	68.61 ± 0.165	17.63 ± 0.414	8.27 ± 0.496	3.95 ± 0.260
	25% FFMW				70.99 ± 0.152	19.44 ± 0.311	5.54 ± 0.370	3.36 ± 0.122
	50% FFMW				70.29 ± 0.261	19.43 ± 0.220	5.78 ± 0.393	4.51 ± 0.069
	75% FFMW				70.52 ± 0.212	20.1 ± 0.578	5.97 ± 0.374	4.39 ± 0.114
	100% FFMW				69.98 ± 0.795	19.45 ± 0.807	7.86 ± 0.411	3.44 ± 1.786
Shire tilapia Oreochromis shiranus [45]	FM	Omnivorous	concrete earthen ponds 126 days	natural conditions	7.70 ± 0.11	51.04 ± 2.10	10.11 ± 0.08	11.13 ± 0.33
	25% FFMW				7.54 0.016	50.30 ± 0.29	10.07 ± 0.02	11.16 ± 0.09
	50% FFMW				7.32 ± 0.02	50.35 ± 0.39	10.10 ± 0.45	11.20 ± 0.73
	75% FFMW				7.20 ± 0.06	50.45 ± 0.70	10.23 ± 0.07	11.32 ± 1.46
Blackspot sea bream (Pagellus bogaraveo) [50]	FM	Omnivorous	flow-through 131 days	natural conditions	70.60	20.45	6.75	1.51
	25% TM				69.65	20.79	7.31	1.52
	50% TM				68.26	21.58	7.440	1.55
Nile tilapia (Oreochromis niloticus) [48]	FM	Omnivorous	biofloc system 42 days	not specified	74.78	54.45	24.11	15.64
	5% TM				74.91	52.18	26.12	15.56
	10% TM				74.39	56.92	25.55	15.31
	15% TM				73.15	50.43	33.08	13.92
	20% TM				72.3	52.31	33.95	14.38
Atlantic Salmon (Salmo salar) [67]	FM	Carnivorous	RAS 84 days	12 h light/ 12 h dark	4.27 ± 0.56	51.34 ± 0.76	39.27 ± 0.66	4.84 ± 0.18
	50% DMW				4.48 ± 0.56	52.40 ± 0.37	37.66 ± 0.67	5.11 ± 0.26
	100% DMW				3.89 ± 0.31	51.35 ± 0.44	39.12 ± 0.87	5.26 ± 0.09
	50% FFMW				3.98 ± 0.54	51.91 ± 1.44	37.22 ± 0.78	5.60 ± 0.44
Sea Bass (Dicentrarchus labrax) [69]	FM	Carnivorous	RAS 70 days	not specified	66.3 ± 0.2	16.9 ± 0.2	11.4 ± 0.6	4.2 ± 0.5
	40% DMW				66.6 ± 0.5	17.4 ± 0.3	11.6 ± 0.3	3.9 ± 0.2
	80% DMW				66.3 ± 0.1	17.1 ± 0.03	12.2 ± 0.3	4.1 ± 0.3
	100% DMW				63.9 ± 0.9	17.0 ± 0.2	14.1 ± 0.7	4.1 ± 0.1
Large Yellow Croakers (Larimichthys crocea) [68]	FM	Carnivorous	floating sea cages 56 days	natural conditions	74.16 ± 0.18	13.65 ± 0.22	7.71 ± 0.26	3.18 ± 0.08
	15% DMW				74.68 ± 0.38	13.44 ± 0.14	7.34 ± 0.23	3.16 ± 0.01
	30% DMW				75.71 ± 0.41	13.59 ± 0.25	7.17 ± 0.02	3.38 ± 0.02
	45% DMW				75.91 ± 0.38	13.56 ± 0.06	7.19 ± 0.10	3.31 ± 0.02

FM, fish meal; DMW, defatted mealworm; FFMW, full-fat mealworm; SBM, Soybean meal; TM, Tenebrio molitor; CP%, Crude protein; CF%, Crude fat.

.

In grass carp (Ctenopharyngodon idellus), it was observed that replacing SBM with TM led to an increase in crude protein (CP%) and a decrease in crude fat (CF%), except in the case of total replacement, where CF% increased [44]. In Nile tilapia, replacing SBM with TM at levels up to 60% led to an increase in the antioxidant capacity of the meat by enhancing SOD, catalase (CAT), and glutathione activities, which could potentially extend the shelf life of the meat [47].

In Pacific white shrimp (Litopenaeus vannamei), dietary inclusion of TM resulted in a significant increase in CP, concomitant with a reduction in the essential fatty acids eicosapentaenoic acid (EPA) and DHA [70]. In Blackspot sea bream (Pagellus bogaraveo), it was found that an increase in dietary TM content was associated with an increase in CF [50].

5. Fish Reproduction

Research on the inclusion of TM in fish broodstock diets remains limited. Although a small number of studies suggest potential improvements in reproductive parameters, the evidence is fragmented and difficult to generalize due to species-specific physiological responses, differences in experimental duration, dietary composition, and inclusion levels. This highlights the need for further controlled studies to establish consistent evidence and practical recommendations.

It was found that supplementation with the methanolic extract of TM had a beneficial effect on reproductive indices, the expression of reproduction-related genes, long-chain polyunsaturated fatty acid (PUFA) biosynthesis, as well as on the gonads of female zebrafish (Danio rerio) [71].

TM larvae can serve as an effective supplemental protein source in broodstock diets, potentially enhancing reproductive performance. Inclusion of TM in place of FM in the diet of Black Sea trout (Salmo labrax), administered two or three times per week, improved gamete quality. Specifically, egg diameter in females and sperm volume in males were significantly increased, while the total number of eggs and other spermatological parameters remained unchanged [72].

6. Blood Biomarkers

In general, the inclusion of FFMW does not negatively affect the red blood cell (RBC) count or the key erythrocyte parameters: mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). However, when FFMW is replaced at levels above 30%, both hemoglobin (Hb) [43], and hematocrit (Hct) [66,73] decrease, which could indicate a slightly reduced oxygen transport capacity. This may occur if the mealworm flour is not processed, as the chitin in FFMW can reduce the digestibility and absorption of minerals and proteins. Some studies have shown that chitin and chitosan can affect iron absorption [74,75], which may explain the decrease in Hb and Hct.

The inclusion of TM flour may lead to an increase in white blood cells (WBC), suggesting a possible stimulation of the immune response or an adaptation of the body to a new diet [76]. In Beluga sturgeon (Huso huso), WBC decreased with the inclusion of TM in the diet [66], most likely due to changes in nutritional intake, considering that SR% was 100% and the fish showed no signs of illness. It has also been found that a high level of chitin has an immunostimulatory effect, activating macrophages, lymphocytes, and other components of innate immunity, which leads to an increase in leukocytes [77]. However, when growth performance decreases and histological changes appear in the intestinal and hepatic tissues, an increase in WBC indicates inflammation. In this context, multiple parameters should be analysed (growth, histological changes, cytokines, IgM, lysozyme, etc.).

One study shows that the inclusion of TM in the diet can stimulate antiparasitic immunity because the structure of the insect exoskeleton resembles that of parasites, thereby training the fish’s immune system [78].

It has been observed that when FM is gradually replaced with DMW, there is a linear increase in blood sodium content in fish [35]. However, if other blood parameters are not affected, this increase may represent a physiological response of the body to the feed change [79].

Replacing FM with more than 30% TM leads to a significant reduction in total protein (TP) and albumin (ALB) concentrations. At substitution levels exceeding 60%, marked increases are observed in malondialdehyde (MDA), protein carbonyls (PC), and 8-hydroxy-2′-deoxyguanosine (8-OHdG), indicating lipid peroxidation and protein oxidation processes associated with cellular membrane damage caused by oxidative stress mechanisms [42,44].

In yellow croaker and Beluga sturgeon it was observed that the activity of hepatic enzymes aspartate aminotransferase (AST) and alanine aminotransferase (ALT) decreased significantly when more than 30% TM was included [42,66], which may suggest immune exhaustion due to the inability to produce enzymes [80]. In grass carp (Ctenopharyngodon idellus), replacing the feed with more than 75% TM led to increased ALT and AST. Elevated enzyme activity indicates liver damage, while significant decreases may signal metabolic dysfunction or heavy metal accumulation [81,82]. In Beluga sturgeon, a significant increase in lymphocyte numbers was observed when the diet was replaced with 40% and 60% TM [66]. The concentration of triglycerides (TG) decreased while TM replacement increased [66].

Table 5. Species-specific hematological responses depending on the level of FM or SBM replacement.

Species and References	Diet	Fish Feeding Habits	Aquaculture System/Period Days	Culture Period/Photoperiod	Hematological Profile	Plasma Biochemical Profile	Antioxidant/ Immunological Profile
Stellate sturgeon Acipenser stellatus [43]	FM	Carnivorous	flow-through 56 days	12 h light/ 12 h dark	-	-	-
	10% FFMW				-	↑ Glu; ↓ TP
	20% FFMW				↑ WBC; ↓ Hct; ↓ Hb	↑ Glu; ↓ TP
	30% FFMW				↑ WBC; ↓ Hct; ↓ Hb	↑ Glu ↑ TG; ↓ TP
Rainbow Trout Oncorhynchus mykiss [35]	FM	Carnivorous	flow-through 91 days	12 h light/ 10 h dark	-	-	-
	25% DMW					-
	50% DMW					↑ Na
	75% DMW					-
	100% DMW					↑ Na
Grass carp Ctenopharyngodon idellus [44]	SBM	Herbivorous	nylon net pond cages 56 days	natural conditions	-		↑ MDA
	25% FFMW				-	↑ ALP; ↑ ACP	↑ GPx, ↑ CAT, ↓ MDA, ↑ IgM
	50% FFMW				-	↑ ALP; ↑ ACP	↑ CAT, ↓ MDA, ↑ ROS, ↑ IgM
	75% FFMW				-	↑ ALT; ↑ AST, ↑ ALP; ↑ ACP	↑ ROS, ↑ MDA, ↑ IgM
	100% FFMW				-	↑ ALT; ↑ AST	↑ ROS, ↑ MDA
Nile tilapia (Oreochromis niloticus) [48]	FM	Omnivorous	biofloc system 42 days	not specified	↓ RBC;	-	-
	5% TM				↓ Hct; ↑ WBC	↓ Glu;	-
	10% TM				↑ Hct;	-	-
	15% TM				↓ PLT	↑ CHOL; ↓ Glu;	-
	20% TM				↓ Hct; ↓ RBC; ↑ WBC; ↓ PLT	↑ TP;	-
Atlantic Salmon (Salmo salar) [67]	FM	Carnivorous	RAS 84 days	12 h light/ 12 h dark	--	↓ TP	↓ IgM
	50% DMW				-	-	↑ IgM; ↓ GPx; ↓ MDA
	100% DMW				-	↑ ALP;	↓ SOD
	50% FFMW				-	↓ ALT; ↑ ALP;	↑ GPx; ↓ SOD
Beluga (Huso huso) [66]	FM	Carnivorous	RAS 56 days	not specified		↓ Glu; ↓ ALB
	20% TM				↓ RBC;	↓ TP
	40% TM					↓ TG; ↑ LDH
	60% TM					↑ CHOL; ↓ AST; ↓ ALT; ↓ ALP; ↑ LDH
	80% TM					↓ ALB; ↑ CHOL; ↓ TG; ↑ LDH
	100% TM				↓ RBC; ↓ Hb; ↓ Hct	↓ ALP; ↑ LDH
Sea Bass (Dicentrarchus labrax) [69]	FM	Carnivorous	RAS 70 days	not specified	-	↓ TP	-
	40% DMW					↑ Glu; ↑ TP; CHOL
	80% DMW					↑ CHOL
	100% DMW					↑ CHOL; ↑ TG

FM, fish meal; DMW, defatted mealworm; FFMW, full-fat mealworm; SBM, Soybean meal; TM, Tenebrio molitor; WBC, white blood cells; Hb, hemoglobin; Hct, hematocrit; ALT, alanin aminotransferase; AST, aspartate aminotransferase; ROS, reactive oxygen species; GPx, glutathione peroxidase; CAT, catalase; RBC, red blood cells; CHOL, Cholesterol; TG, Triglyceride; TP, Total protein; ALP, alkaline phosphatase; IgM, immunoglobulin M; Glu, Glucose; MDA, Malondialdehyde; ACP, Acid phosphatase; PLT, Platelets; SOD, superoxide dismutase; ALB, Albumin; LDH, Lactate Dehydrogenase.

presents the hematological parameters of various species in response to different levels of FM and SBM replacement.

Additionally, when TM replacement exceeds 75%, the activity of antioxidant enzymes glutathione peroxidase (GPx) and superoxide dismutase (SOD) decreases significantly [44] as a result of prolonged stress exposure [83]. In Nile tilapia (Oreochromis niloticus), replacing SBM with TM stimulates hepatic antioxidant performance by increasing SOD activity [47].

Regarding proteolytic enzyme activity, it has been observed that including 10% TM can stimulate trypsin activity, but at levels above 20–30%, its activity decreases significantly [43].

In Zebrafish (Danio rerio), dietary supplementation with the bioactive substance derived from mealworm larvae at a concentration of 100 μg/g has the potential to enhance resistance to bacterial infections by modulating the immune response [84].

7. Histopathological Changes

Histological changes were observed in the intestine, liver, and kidney, depending on the percentage of FM replaced with TM.

7.1. Intestine Histopathology

Several studies support that with an increasing proportion of TM in the fish diet, an increase in lamina propria (LP) thickness has been observed [35,44] while at levels above 45% TM, infiltration of inflammatory cells and a decrease in goblet cell density in the intestinal tissue occur [35,42]. In some studies, no significant differences were observed between groups regarding eosinophilic granulocytes (EG), goblet cells (GC), mucosal fold fusion (MFF), subepithelial mucosa (SeM), and supranuclear vacuoles (SV) [35]. Villus height at 30% TM shows maximum height and width, but at TM substitution levels above 45%, a significant reduction is observed [42,44]. This reduction in villus size leads to decreased nutrient absorption from the feed [85,86,87].

In Nile tilapia, supplementation with sodium butyrate in both FM- and TM-based diets markedly enhanced intestinal histomorphology, as evidenced by increased villus height and branching. These modifications suggest an expanded absorptive surface, potentially improving nutrient digestion and utilization efficiency [88].

7.2. Liver Histopathology

With the increase in the percentage of TM in the fish diet, small changes in rare lymphocyte aggregates in the tissue or in the portal areas were observed. When replaced with 25% and 50% DMW, the lowest prevalence of lymphocytic inflammation was observed [35]. However, at 60–100% TM inclusion, severe degradation occurs, including cell swelling, lipid vacuolation, and infiltration of inflammatory cells [42].

A recent study demonstrated that the inclusion of TM induces species-specific alterations in hepatic protein abundance, with gilthead seabream exhibiting fewer affected proteins compared to European seabass and rainbow trout [36]. Therefore, it is recommended to investigate the effects of TM inclusion according to species and replacement level.

7.3. Kidney Histopathology

From a morphological perspective, the kidney exhibits a normal structure, with hematopoietic tissue interspersed between the tubules and only minimal to mild parenchymal pathology. It was observed that increasing the percentage of DMW in the fish diet led to occasional mineralization, which replaced the tubules and was encased by a thin layer of fibrous tissue [35].

Table 6. Species-specific histological changes associated with different levels of FM or SBM replacement.

Species and References	Diet	Fish Feeding Habits	Aquaculture System/Period Days	Culture Period/Photoperiod	Histological Changes
Rainbow Trout Oncorhynchus mykiss [35]	FM	Carnivorous	flow-through 91 days	12 h light/ 10 h dark	Liver—rare lymphocyte aggregates
	25% DMW				LP ↑—Distal intestinal inflammation
	50% DMW
	75% DMW				LP ↑—Distal intestinal inflammation Liver—sparse lymphocyte aggregates Kidney—tubular mineralization
	100% DMW				LP ↑—Distal intestinal inflammation Liver—rare lymphocyte aggregates Kidney—tubular mineralization
Grass carp Ctenopharyngodon idellus [44]	SBM	Herbivorous	nylon net pond cages 56 days	natural conditions	-
	25% FFMW				↑ intestinal fold height
	50% FFMW
	75% FFMW				↓ intestinal fold height, ↓ muscle thickness, ↓ intestinal goblet cell numbers;
	100% FFMW
Nile Tilapia (Oreochromis niloticus) [88]	FM+SB	Omnivorous	glass aquaria (100 L) 60 days	not specified	↑ Villus height; ↑ Villus width; ↑ Crypt depth; ↑ Muscularis thickness; ↑ Goblet cell count
	FM-SB				-
	TM+SB				↑ Villus height; ↑ Villus width; ↑ Crypt depth; ↑ Muscularis thickness; ↑ Goblet cell count
	TM-SB				-
Sea Bass (Dicentrarchus labrax) [69]	FM	Carnivorous	RAS 70 days	not specified	-
	40% DMW				↑ submucosa thickness
	80% DMW				↑ submucosa thickness
	100% DMW				↑ submucosa thickness
Large Yellow Croakers (Larimichthys crocea) [68]	FM	Carnivorous	floating sea cages 56 days	natural condition
	15% DMW				↑ Villus height;
	30% DMW				↑ Villus thickness; ↑ Muscularis thickness; ↓ DAO
	45% DMW				↑ Villus height; ↑ Villus thickness; ↑ Muscularis thickness; ↓ DAO

FM, fish meal; DMW, defatted mealworm; FFMW, full-fat mealworm; SBM, Soybean meal; TM, Tenebrio molitor; LP, lamina proprie; SB, Sodium butyrate; DAO, diamine oxidase.

presents the species-specific histological changes associated with different levels of FM or SBM replacement by TM meal.

8. Intestinal Microbiota

In the yellow croaker fed with 15%, 30%, 45%, and 60% TM, the intestinal microbiota was mainly dominated by the phyla Proteobacteria, Firmicutes, and Fusobacteria [42]. The most abundant genera were Fusobacterium, Lactobacillus, Ralstonia, Providencia, and Cetobacterium. However, their proportions varied when a higher proportion of TM was included in the fish diet. Specifically, the abundance of Lactobacillus and Providencia decreased, while the populations of Ralstonia and Cetobacterium significantly increased compared to the control group. Fish with predominantly Lactobacillus had the best growth rates and feed conversion ratios, whereas the groups with higher levels of TM inclusion were dominated by Ralstonia and recorded the lowest growth rates [42].

In European seabass (Dicentrarchus labrax), dietary inclusion of a blended insect meal derived from Hermetia illucens and TM at levels of 25% and 50% was associated with a trend toward increased bacterial richness and diversity, notably within the beneficial genera Bacillus and Paenibacillus [89]. The dominant phyla across treatments were Firmicutes and Proteobacteria, with a reduction in Firmicutes observed in the 25% inclusion group and a decrease in Proteobacteria in the 50% inclusion group [89].The differential impact of FM replacement with TM meal on the intestinal bacterial community structure appears to be species-specific. In gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax), TM inclusion in the diet resulted in an increase in the number of operational taxonomic units (OTUs), whereas in rainbow trout (Oncorhynchus mykiss), a decrease was observed. Moreover, in both S. aurata and D. labrax, the dietary replacement led to the emergence of numerous novel bacterial taxa that were absent in the control diets [90]. Another study demonstrated that the complete replacement of FM with TM meal does not exert negative effects on the intestinal and skin-associated microbial communities of rainbow trout. However, consistent with the findings reported in the previous study, a reduction in the relative abundance of microbial taxa, specifically the genus Deefgea (family Neisseriaceae), was observed in both the gut and skin microbiota [91]. In Largemouth bass, dietary inclusion of TM at levels up to 24% enhances intestinal health and immunity through activation of NFκBp65 and upregulation of surviving expression, thereby inhibiting apoptosis [92].

9. Recommendations and Mitigation Strategies

Based on a comprehensive review of the specialized literature, the following recommendations can be formulated:

It is advisable to transition gradually from a commercial feed to a mealworm-based diet. This allows the fish to adapt and prevents an intestinal inflammatory response. Also, processing TM meal is recommended, along with supplementing it with additional nutrients to prevent nutritional imbalances. These imbalances could lead to health issues and risks such as intestinal inflammation, liver damage, renal mineralization, and more.

When TM is included in the diet in the form of FFMW, a replacement of up to 10% is recommended; beyond this level, growth performance declines due to reduced metabolic efficiency.

Replacing more than 50% of FM with TM in the diet is not recommended, as studies have shown that it can compromise both growth and overall fish health, leading to increased oxidative stress and the occurrence of cellular lesions [42]. Additionally, at inclusion levels of 60–100% TM, there is a reduction in beneficial bacterial populations (Lactobacillus) and an increase in potentially harmful bacteria (Ralstonia) [42].

9.1. Processing of Tenebrio molitor Meal and Nutrient Supplementation

Processing TM meal through different methods (dechitinization, fermentation, and enzymatic hydrolysis) improves fish digestion, nutrient absorption, and physiological responses [93,94,95].

TM hydrolysate represents a highly beneficial alternative functional protein supplement for both human nutrition and aquaculture. The use of nuruk extract concentrate as a natural enzyme for hydrolyzing TM proteins has been shown to enhance protein digestibility, bioactivity, and sensory attributes compared to commercial proteases such as alcalase and flavourzyme [93]. Also, the TM protein hydrolysate, especially the >10 kDa fraction, has antioxidant, anti-inflammatory, and muscle-protective properties comparable to whey protein isolate, suggesting its potential as an alternative functional protein supplement in aquaculture and human nutrition [96].

Fermentation of TM with commercial lactic acid bacteria starters, especially TCC-4 (Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus) as well as FLORA DANICA (Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis biovar diacetylactis, Lactococcus lactis subsp. lactis, Leuconostoc), ST-BODY-1 (thermophilic lactic acid culture), YC-380 (Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus), and ABY-3 (Bifidobacterium, Lactobacillus acidophilus, Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus), can enhance digestibility, protein and fat hydrolysis, as well as antioxidant and sensory properties, producing a more valuable product for human consumption or aquaculture feed [94].

To reduce the risk of intestinal inflammation and thickening of the lamina propria (LP), it is recommended to process, treat, and pelletize TM meal. Also, to prevent an increase in crude fat content in the fish flesh, it is recommended to defat the mealworm, as this reduces lipid load and potential metabolic variations. The processing should be carried out using environmentally friendly methods whenever possible [97]. Dechitinizing mealworm meal enhances nutrient absorption by improving digestibility. Furthermore, pelletizing TM in the feed enhances its nutritional quality [95].

The nutritional quality of feed and food produced with mealworms (TM) can be optimised by selecting the substrate on which the mealworm larvae are reared [98,99].

When mealworm is the only protein source, supplementation with cysteine and taurine is recommended [35]. According to Anany et al. (2023), the inclusion of S. cerevisiae in TM meal is recommended for its beneficial effects on intestinal, hepatic, and immune health, as well as its capacity to mitigate oxidative stress [76]. In the Pacific white shrimp (Litopenaeus vannamei), dietary lipid supplementation is recommended to preserve optimal fatty acid profiles [70].

9.2. Osmoregulation

If more than 50% of FM is replaced with DMW, strict control of dietary sodium intake is recommended to prevent excessive plasma sodium accumulation and to support effective physiological adaptation in fish [100]. To precisely determine whether the rise in sodium is a physiological adaptation to the new feed or a result of other factors, it is advisable to monitor serum osmolality, hematocrit, urea, creatinine, and base excess, while also supplementing the feed with electrolytes to maintain a balanced Na/K/Cl ratio and prevent sodium overload.

However, these recommendations are limited by short to medium-term studies, species-specific responses, and variability in TM composition depending on substrate, processing, and larval stage. Further research is needed to validate long-term safety, optimize inclusion levels across species, and assess interactions with environmental and dietary factors.

10. Conclusions

Fish feed based on TM represents a rich source of protein. TM-based diets provide higher levels of essential amino acids (EAA: isoleucine, leucine, lysine, methionine, threonine, valine) and non-essential amino acids (NEAA: alanine, glycine, and proline) compared to SBM-based diets. The inclusion of TM in fish diets is not recommended without proper processing, as processing enhances its digestibility and nutrient absorption, leading to improved growth performance in fish.

Recent studies have shown that substituting more than 50% of fishmeal with TM in fish diets can lead to metabolic imbalances, disrupt electrolyte profiles, and negatively affect hematological and biochemical parameters, as well as the morpho-histological structure of the digestive system, liver, and kidneys. To achieve optimal growth performance, maintain good physiological status, and ensure high-quality flesh in fish, TM should be included in diets at species-specific levels of 10–30%. When used as a partial replacement for fishmeal, an inclusion rate of up to 50% is generally considered optimal, while substitution for SBM is recommended at 25–30%.

Although current evidence indicates that dietary inclusion of TM can enhance intestinal health and immune function in fish, these conclusions are constrained by the short duration of existing studies, species-specific responses, and variability in TM composition resulting from differences in substrate, processing, and larval stage. Consequently, further systematic investigations are warranted to clarify the long-term safety of TM, establish optimal inclusion levels across different species, and evaluate interactions with environmental conditions (such as rearing system, photoperiod, and water quality) as well as with dietary supplementation, including essential nutrients and functional additives.