1. Introduction

Schizothorax wangchiachii belongs to the genus Schizothorax (Cyprinidae: Schizothoracinae) within the order Cypriniformes. It is primarily distributed in the Jinsha, Wujiang, and Yalong Rivers of China. Wild populations of this species have declined significantly due to overfishing, environmental pollution, and hydropower development.1,2 To protect this species and mitigate its population decline, researchers have successfully overcome bottlenecks in its artificial domestication3 and breeding.4 Subsequent studies have explored its reproductive capacity,5 oviposition behavior,6 embryonic development,7 and larval rearing.8 Currently, the artificial farming of S. wangchiachii has reached commercial scale in southwestern China, with limited quantities available in the market. Wang et al. analyzed the whole-body nutritional composition of S. wangchiachii fry, highlighting its high edible value and development potential.9 Similarly, Lu et al. evaluated the nutritional profile of its dorsal muscle and identified it as a high-quality protein source for human consumption.10 However, consumers rarely eat fish fry or isolate the dorsal muscle; the fish is typically cooked and consumed whole.

To further investigate the nutritional composition of S. wangchiachii muscle, this study examined fish of three different sizes. These fish were reared under semi-natural conditions at the Jinping-Guandi Fish Proliferation and Release Station on the Yalong River. We measured and analyzed the proximate composition, amino acids, fatty acids, and mineral elements of the whole-body muscle, and conducted an amino acid nutritional evaluation. This study aims to comprehensively reveal the nutritional value and characteristics of S. wangchiachii, providing a theoretical basis for its aquaculture and commercial development.

2. Materials and Methods

2.1. Materials

The Jinping-Guandi Fish Proliferation and Release Station is located on the left bank of the Dahewan reach of the Yalong River. The station directly extracts river water from Dahewan to supply its circular fish tanks. Semi-natural aquaculture is conducted in these tanks, using the inflowing water to generate a continuous circular current. On August 15, 2023, a total of 14 Schizothorax wangchiachii were collected from these tanks for use as experimental samples. The fish were categorized into three size groups: small, medium, and large. After assigning the fish to these experimental groups, their ages were determined by observing their anal scales.5 The basic parameters of S. wangchiachii of three different sizes reared under semi-natural conditions are shown in Table S1.

2.2. Determination of biological characteristics

The body mass (MT, 0.01 g) and total length (LT, 0.01 cm) of the experimental fish were measured. The fish were then dissected to remove the viscera, gills, and skin, and the remaining body was weighed (MB, 0.01 g). The majority of the muscle tissue was excised and cooked to separate the meat from the bones. All bones were carefully extracted, air-dried naturally, and weighed (MS, 0.01 g). Meat content was calculated using the following equation.

\[Meat\ content\ (\%) = \frac{M_{B} - M_{S}}{M_{T}} \times 100\]

2.3. Determination of proximate composition in muscle

The excised fish muscle was deboned, minced, and homogenized for nutritional analysis. Proximate composition was determined using Chinese National Standard (GB) methods. Moisture was determined via the direct drying method (GB 5009.3-2010). Crude protein and crude lipid were determined using the Soxhlet extraction method (GB 5009.5-2010 and GB/T 5009.6-2003, respectively). Crude fiber and ash contents were measured according to the Chinese National Standard methods (GB/T 6433-2006 and GB/T 6438-2007, respectively). For nutritional profiling, amino acids were analyzed using an Agilent HPLC-1200 high-performance liquid chromatography auto-analyzer (GB 5009.124-2003). Fatty acids were determined using an Agilent GC7890 gas chromatograph (GB/T 22223-2008). Sodium and potassium were determined by flame emission spectrometry (GB/T 5009.91-2003). Iron, magnesium, manganese, calcium, copper, and zinc were analyzed using atomic absorption spectrophotometry (GB/T 5009.90-2003, GB/T 5009.92-2003, GB/T 5009.13-2003, and GB/T 5009.14-2003). Selenium was determined using the fluorometric method (GB 5009.93-2010).

2.4. Evaluation of the nutritional value of fish muscle

The contents of the nine essential and semi-essential amino acids measured in the muscle were converted to milligrams of amino acid per gram of nitrogen. These values were then compared with the Food and Agriculture Organization/World Health Organization (FAO/WHO) scoring pattern and the whole egg protein scoring pattern. The amino acid score (AAS), chemical score (CS), and essential amino acid index (EAAI) were calculated based on these comparisons.

AAS and CS were calculated using the following equation.

\[Score = \frac{aa}{AA}\]

For the AAS calculation, aa represents the amino acid content in the sample and AA represents the amino acid content in the FAO/WHO reference pattern. For the CS calculation, aa is the amino acid content in the sample and AA is the corresponding amino acid content in whole egg protein.

The EAAI was calculated using the following equation.

\[EAAI = \left\lbrack \prod_{i = 1}^{n}{(\frac{100 \times {aa}_{i}}{{AA}_{i}})} \right\rbrack^{\frac{1}{n}}\]

In this EAAI equation, aai represents the content of the i-th amino acid in the test sample. AAi represents the content of the corresponding i-th amino acid in the whole egg protein standard. The variable n indicates the total number of amino acids evaluated.

2.5. Data statistical analysis

Statistical analysis was performed using Microsoft Excel 2019 and SPSS 19.0. All data are presented as the mean ± standard deviation (SD). Differences among the three size groups were analyzed using a one-way analysis of variance (ANOVA), followed by Tukey’s HSD post-hoc test for multiple comparisons. Significant differences among groups are denoted by P < 0.05.

3. Results

3.1. Proximate Composition

As shown in Table S2, there were no significant differences in meat content, muscle moisture, crude fiber, and crude protein among the three sizes of fish (P > 0.05). The mean values for these parameters were 76.36 ± 2.12%, 76.21 ± 0.68%, 0.10 ± 0.01%, and 19.32 ± 0.61%, respectively. However, significant differences were observed in the crude lipid and ash contents (P < 0.05). The levels of these components followed the order of medium > small > large size. The overall mean values for crude lipid and ash were 2.01 ± 0.15% and 2.00 ± 0.15%, respectively.

3.2. Muscle amino acid composition and content

As shown in Table 1, a total of 18 amino acids were detected in the muscle of Schizothorax wangchiachii. These included 8 essential amino acids (EAA), 1 semi-essential amino acid, 9 non-essential amino acids (NEAA), and 6 flavor amino acids (DAA). Significant differences were found in the total amino acid and total essential amino acid contents among the three sizes of fish (P < 0.05). The contents of both parameters followed the order of large > small > medium size. The overall mean values were 145.95 ± 11.28 mg/g and 58.16 ± 3.52 mg/g, respectively. There were no significant differences in the NEAA and DAA contents between the small and medium fish (P > 0.05). However, the contents in both of those groups were significantly lower than those in the large fish. The overall mean values for NEAA and DAA contents across the three sizes were 87.79 ± 7.94 mg/g and 71.86 ± 7.83 mg/g, respectively.

Table 1.Amino acid composition and content in the muscle of S. wangchiachii (fresh weight, n = 3, mg/g)
Amino acids Small Size Medium Size Large Size Mean
NEAA Glu △ 21.17 ± 0.03a 21.34 ± 0.15a 27.84 ± 0.31b 23.45 ± 3.11
Asp △ 12.54 ± 0.00a 12.46 ± 0.09a 18.19 ± 0.19b 14.4 ± 2.68
Ala △ 9.80 ± 0.06a 9.96 ± 0.08a 12.76 ± 0.15b 10.84 ± 1.36
Arg 10.41 ± 0.01a 10.29 ± 0.08a 10.47 ± 0.12a 10.39 ± 0.11
Tyr △ 8.73 ± 0.00a 8.02 ± 0.07b 10.15 ± 0.11c 8.97 ± 0.89
Ser 6.54 ± 0.01a 6.51 ± 0.06a 6.79 ± 0.07c 6.61 ±0.14
Pro 6.20 ± 0.02a 6.58 ± 0.07b 5.79 ± 0.06c 6.19 ± 0.33
Gly △ 5.89 ± 0.01a 6.40 ± 0.05b 6.22 ± 0.07c 6.17 ± 0.22
Cys 0.80 ± 0.00a 0.76 ± 0.01b 0.76 ± 0.01b 0.77 ± 0.02
EAA Leu 11.98 ± 0.01a 11.42 ± 0.09b 13.55 ± 0.15c 12.32 ± 0.91
Lys 9.29 ± 0.01a 9.23 ± 0.06a 14.88 ± 0.16b 11.13 ± 2.65
Ile 10.54 ± 0.02a 9.80 ± 0.09b 8.87 ± 0.09c 9.74 ± 0.69
Phe △ 8.67 ± 0.01a 7.70 ± 0.09b 7.72 ± 0.08b 8.03 ± 0.46
Thr 6.48 ± 0.01a 6.08 ± 0.06b 6.55 ± 0.07a 6.37 ± 0.21
His * 3.92 ± 0.02a 3.46 ± 0.01b 3.40 ± 0.05b 3.59 ± 0.23
Met 2.84 ± 0.00a 2.99 ± 0.03b 3.90 ± 0.04c 3.24 ± 0.47
Val 3.06 ± 0.00a 2.95 ± 0.03b 3.35 ± 0.03c 3.12 ± 0.17
Trp 0.68 ± 0.01a 0.65 ± 0.00b 0.53 ± 0.01c 0.62 ± 0.07
TAA 139.54 ± 0.04a 136.6 ± 1.12b 161.72 ± 1.77c 145.95 ± 11.28
EAA 57.45 ± 0.05a 54.28 ± 0.46b 62.74 ± 0.68c 58.16 ± 3.52
NEAA 82.08 ± 0.01a 82.33 ± 0.66a 98.97 ± 1.09b 87.79 ± 7.94
DAA 66.81 ± 0.05a 65.89 ± 0.54a 82.88 ± 0.91b 71.86 ± 7.83
∑NEAA/∑TAA (%) 58.83 ± 0.03a 60.27 ± 0.01b 61.20 ± 0.01c 60.10 ± 0.98
∑EAA/∑TAA (%) 41.17 ± 0.03a 39.73 ± 0.01b 38.80 ± 0.01c 39.90 ± 0.98
∑DAA/∑TAA (%) 47.88 ± 0.05a 48.23 ± 0.00b 51.25 ± 0.01c 49.12 ± 1.51

Note: △ represents flavor amino acids, * represents semi-essential amino acid.

Glutamic acid showed the highest content (23.45 ± 3.11 mg/g) in the muscle of all three sizes of fish. The contents of arginine, aspartic acid, alanine, isoleucine, leucine, and lysine were relatively high. Their levels were close to or greater than 10 mg/g. The contents of serine, proline, glycine, tyrosine, phenylalanine, and threonine ranged from 6 to 9 mg/g. The contents of valine, methionine, and histidine were relatively low at slightly above 3 mg/g. The contents of cystine and tryptophan were notably lower than those of other amino acids. The levels of both were below 1 mg/g.

3.3. Muscle fatty acid composition and content

As shown in Table 2, a total of 30 fatty acids were detected in the muscle of S. wangchiachii. These included 11 saturated fatty acids (SFAs) and 19 unsaturated fatty acids (UFAs). The UFAs consisted of 9 monounsaturated fatty acids (MUFAs) and 10 polyunsaturated fatty acids (PUFAs). Additionally, two trans fatty acids were identified in the muscle. These were trans-oleic acid and trans-linoleic acid. The total percentage of SFAs increased significantly with increasing fish size (P < 0.05). Conversely, the total percentages of UFAs and PUFAs decreased significantly as fish size increased (P < 0.05). Significant differences were also observed in the total percentage of MUFAs among the three sizes (P < 0.05). This percentage followed the order of medium > small > large size.

Table 2.Fatty acid composition and content in the muscle of S. wangchiachii (fresh weight, n=3, %)
Fatty acids Small Size Medium Size Large Size Mean
C6:0 0.37±0.01a 0.56±0.04b 0.59±0.03b 0.51±0.10
C8:0 0.37±0.02a 0.66±0.02a 0.67±0.01b 0.57±0.14
C10:0 0.27±0.02a 0.56±0.02b 0.72±0.04c 0.52±0.19
C12:0 0.24±0.00a 0.48±0.08b 0.51±0.01b 0.41±0.13
C14:0 0.70±0.01a 0.54±0.04b 1.23±0.07c 0.82±0.30
C14:1 0.13±0.01a 0.20±0.01b 0.30±0.05c 0.21±0.08
C15:0 0.11±0.01a 0.12±0.02ab 0.16±0.01b 0.13±0.03
C15:1 0.71±0.02a 1.33±0.04b 1.34±0.07b 1.13±0.30
C16:0 15.60±0.07a 14.19±0.03b 22.07±0.05c 17.29±3.43
C16:1 1.68±0.01a 0.82±0.04b 2.57±0.08c 1.69±0.72
C17:0 0.22±0.01a 0.22±0.01a 0.24±0.03a 0.23±0.02
C17:1 0.23±0.01a 0.62±0.04b 0.43±0.02c 0.43±0.16
C18:0 7.70±0.08a 8.41±0.02b 11.32±0.12c 9.14±1.57
C18:1 Trans 0.10±0.01a 0.28±0.06a 0.36±0.01b 0.25±0.11
C18:1 21.53±0.16a 21.02±0.14b 14.15±0.45c 18.9±3.38
C18:2 Trans 0.07±0.01a 0.21±0.02b 0.06±0.01a 0.12±0.07
C18:2 22.33±0.15a 15.75±0.02b 15.00±0.02c 17.69±3.29
C18:3 n-6 0.91±0.03a 0.38±0.03b 0.90±0.20a 0.73±0.27
C18:3 n-3 4.80±0.05a 7.05±0.04b 1.41±0.04c 4.42±2.32
C20:0 0.98±0.04a 1.60±0.05b 1.81±0.32b 1.46±0.40
C20:1 n-9 3.48±0.02a 3.02±0.04b 1.47±0.15c 2.65±0.86
C20:2 0.83±0.10a 0.49±0.01b 0.59±0.12ab 0.64±0.17
C20:3 n-6 1.23±0.02a 0.90±0.07b 1.40±0.04c 1.18±0.21
C20:4 n-6 3.65±0.03a 5.10±0.04b 7.31±0.38c 5.35±1.52
C20:3 n-3 0.09±0.01a 0.20±0.03b 0.94±0.41b 0.41±0.45
C20:5 6.24±0.13a 8.49±0.08b 0.63±0.08c 5.12±3.31
C22:0 0.33±0.00a 0.61±0.02b 0.85±0.19b 0.60±0.24
C22:1 0.11±0.01a 0.26±0.05b 0.13±0.01a 0.17±0.07
C22:2 0.08±0.00a 0.46±0.03b 0.16±0.01c 0.23±0.17
C24:1 4.90±0.09a 5.48±0.21b 10.68±0.57c 7.02±2.62
∑SFA 26.91±0.14a 27.96±0.16b 40.16±0.73c 31.67±6.03
∑UFA 73.09±0.14a 72.04±0.16b 59.84±0.73c 68.33±6.03
∑MUFA 32.88±0.20a 33.01±0.05b 31.42±0.47c 32.44±0.78
∑PUFA 40.22±0.20a 39.03±0.12b 28.41±0.27c 35.89±5.31

Palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2) showed the highest contents in the muscle across all three sizes. Their mean values were all above 17%. The contents of stearic acid (C18:0), α-linolenic acid (C18:3 n-3), tetracosenoic acid (C24:1), arachidonic acid (C20:4 n-6), and eicosapentaenoic acid (C20:5) were relatively high. These levels ranged from 4% to 10%. The contents of pentadecenoic acid (C15:1), palmitoleic acid (C16:1), eicosanoic acid (C20:0), eicosenoic acid (C20:1 n-9), and eicosatrienoic acid (C20:3 n-6) ranged from 1% to 3%. The contents of caproic acid (C6:0), caprylic acid (C8:0), myristic acid (C14:0), capric acid (C10:0), linolenic acid (C18:3 n-6), eicosadienoic acid (C20:2), and behenic acid (C22:0) were relatively low. These levels ranged from 0.5% to 1%. The contents of heptadecenoic acid (C17:1) and all other remaining fatty acids were below 0.5%.

3.4. Muscle mineral element composition and content

As shown in Table 3, a total of 9 mineral elements were detected. These included 3 major elements and 6 trace elements. Among the major elements, potassium showed the highest content at 2.75 ± 0.08 mg/g. The contents of calcium and magnesium were both less than 2 mg/g. Among the trace elements, zinc had the highest content at 9.04 ± 0.20 mg/kg. This was followed by iron at 8.12 ± 0.26 mg/kg. The contents of copper, chromium, manganese, and selenium were all less than 1 mg/kg.

Table 3.Mineral element composition in the muscle of S wangchiachii (fresh weight, n=3)
Elements Small Size Medium Size Large Size Mean
Major elements (mg/g) K 2.70±0.04a 2.86±0.03b 2.69±0.03a 2.75±0.08
Ca 1.32±0.00a 1.21±0.01b 1.21±0.01b 1.25±0.05
Mg 0.23±0.00a 0.24±0.00b 0.24±0.00b 0.24±0.00
Trace elements (mg/kg) Zn 9.16±0.17ab 9.14±0.04a 8.82±0.12b 9.04±0.20
Fe 8.73±0.09a 8.45±0.07b 8.27±0.05c 8.12±0.26
Cu 1.00±0.01a 0.95±0.01b 1.01±0.01a 0.99±0.03
Cr 0.80±0.01a 0.76±0.01b 0.68±0.01c 0.75±0.05
Mn 0.20±0.00a 0.18±0.00b 0.18±0.00c 0.19±0.01
Se 0.15±0.00a 0.15±0.00a 0.13±0.00b 0.14±0.01

4. Discussion

4.1. Evaluation and comparison of proximate composition

The edible portion of a fish consists primarily of its body muscle. Therefore, meat yield is a crucial indicator for evaluating its economic value and production performance.11 Based on the results of the present study and data from the literature, the muscle proximate compositions of S. wangchiachii and several other fish species are summarized in Table S3. The meat yield of S. wangchiachii is higher than that of common edible freshwater fishes. These include Mylopharyngodon piceus, Ctenopharyngodon Idella, Aristichthys nobilis, and Cyprinus carpio. It is also higher than that of several other Schizothorax species, such as S. kozlovi Nikolsky and S. griseus. The muscle crude protein content of S. wangchiachii is higher than that of M. piceus, A. nobilis, C. carpio, S. prenanti, and S. kozlovi Nikolsky. However, it is slightly lower than that of C. idella. The muscle crude lipid content of S. wangchiachii is significantly lower than that of C. carpio and S. chongi. Conversely, it is higher than that of C. idella, A. nobilis, M. piceus, S. prenanti, S. kozlovi Nikolsky, and S. griseus. Overall, S. wangchiachii is a high-quality edible fish characterized by its high meat yield and high protein content.

4.2. Nutritional evaluation and comparison of amino acids

The ratio of essential amino acids to total amino acids (EAA/TAA) in the muscle of S. wangchiachii is 39.90% (Table 1). Additionally, based on our calculations, the ratio of essential to non-essential amino acids (EAA/NEAA) was 66.24%. These values are lower than the results reported by Wang et al.9 for the whole body of S. wangchiachii fry. Their reported EAA/TAA and EAA/NEAA were 46.4% and 86.57%, respectively. Additionally, our results are lower than those reported by Lu et al.10 for the dorsal muscle of this species. The EAA/TAA and EAA/NEAA in that study were 40.15% and 71.5%, respectively. According to the ideal amino acid pattern described by the Food and Agriculture Organization and the World Health Organization (FAO/WHO), a high-quality protein source should have an EAA/TAA ratio of approximately 40% and an EAA/NEAA ratio greater than 60%. Based on these criteria, the amino acid composition of S. wangchiachii is considered ideal. Therefore, it serves as a high-quality protein source.

As shown in Table 4, the limiting amino acids in the muscle of S. wangchiachii exhibited dynamic changes with increasing body size. In the small- and medium-sized groups, valine had the lowest AAS (0.51 and 0.49, respectively) and was identified as the first limiting amino acid. This aligns with the findings of Wang et al.9 regarding the nutrition of juvenile S. wangchiachii. Tryptophan (AAS: 0.58 and 0.56) and methionine + cystine (AAS: 0.85 and 0.88) were the second and third limiting amino acids, respectively. However, in the large-sized group, tryptophan became the first limiting amino acid (AAS: 0.45; CS: 0.28). Valine shifted to the second limiting amino acid (AAS: 0.56). Meanwhile, the score of methionine + cystine increased to 1.09, indicating it was no longer a limiting factor. Furthermore, isoleucine showed high AAS and CS, reaching 2.17 and 1.64 in the small-sized group, respectively. Lysine also exhibited excellent values, with its AAS and CS reaching up to 2.25 and 1.74 in the large-sized group, respectively. Lysine participates in body protein synthesis and is closely related to animal growth, earning it the title of “growth amino acid”.12 Therefore, consuming S. wangchiachii can supplement human lysine needs and promote protein utilization.

Table 4.AAS and CS of essential amino acids in S. wangchiachii
EAA
(mg/g)		 Small Size Medium Size Large Size FAO/WHO Whole egg protein AAS CS
Small Size Medium Size Large Size Small Size Medium Size Large Size
Thr 6.48 6.08 6.55 2.50 2.92 1.33 1.25 1.35 1.14 1.07 1.16
Val 3.06 2.95 3.35 3.10 4.10 0.51 0.49 0.56 0.38 0.37 0.42
Ile 10.54 9.80 8.87 2.50 3.31 2.17 2.02 1.83 1.64 1.52 1.38
Leu 11.98 11.42 13.55 4.40 5.34 1.40 1.34 1.59 1.16 1.10 1.31
Lys 9.29 9.23 14.88 3.40 4.41 1.41 1.40 2.25 1.08 1.08 1.74
Trp 0.68 0.65 0.53 0.60 0.99 0.58 0.56 0.45 0.35 0.34 0.28
Met + Cys 3.64 3.75 4.66 2.20 3.86 0.85 0.88 1.09 0.49 0.50 0.62
Phe + Tyr 17.40 15.72 17.87 3.80 5.65 2.36 2.13 2.42 1.59 1.43 1.63
EAAI 71.19 70.73 71.99

The glutamic acid content in the muscle reached a high level of 2.35%. Glutamic acid is recognized as the amino acid with the strongest umami flavor. Meanwhile, the total content of flavor amino acids (DAAs) in the muscle reached 7.19%. These DAAs include glutamic acid, aspartic acid, phenylalanine, alanine, glycine, and tyrosine. This DAA value is significantly higher than that of the whole body of S. wangchiachii fry (4.35%)9 and its dorsal muscle (4.69%).10 It is also higher than that of M. piceus (6.08%),13 C. idella (5.48%),14 S. prenanti (6.26%),15 and S. chongi (4.45%).16 Furthermore, this DAA content is similar to that of several common freshwater fishes. These similar species include C. carpio (6.86%),17 Carassius auratus (6.99%),17 Hypophthalmichthys molitrix (7.00%),18 A. nobilis (7.08%),18 and Pelteobagrus vachelli (7.16%).19 Based on these results, it can be inferred that S. wangchiachii presents a highly delicious umami flavor after cooking. Overall, the scores of lysine and certain limiting amino acids (e.g., methionine + cystine) were improved in the muscle of large-sized S. wangchiachii. Additionally, the contents of glutamic acid and flavor amino acids in this group were higher than those in the small- and medium-sized groups.

4.3. Nutritional evaluation and comparison of fatty acids

Lipids are primarily composed of fatty acids. The composition and content of fatty acids determine the nutritional value and taste of fish.20,21 Monounsaturated fatty acids function to lower blood sugar and cholesterol levels. They also regulate blood lipids. Polyunsaturated fatty acids are involved in various physiological and biochemical processes. They are essential nutrients for human metabolism. The muscle of S. wangchiachii contains 30 fatty acids. These include 19 unsaturated fatty acids accounting for 68.33% of the total content. This value is lower than that of the whole body of S. wangchiachii fry (70.25%)9 and its dorsal muscle (72.44%).10 It falls within an intermediate range when compared to common freshwater fish. These fish species include M. piceus (70.99%),13 C. idella (65.12%),14 H. molitrix (66.98%),18 A. nobilis (68.07%),18 C. carpio (70.36%),17 and C. auratus (72.81%).17 It is also intermediate compared to other Schizothorax species, such as S. prenanti (76.18%)15 and S. chongi (73.58%).16 The muscle of S. wangchiachii contains 32.44% monounsaturated fatty acids and 35.89% polyunsaturated fatty acids. Among these, the content of n-3 polyunsaturated fatty acids reaches a high level of 10.27%. Within the n-3 polyunsaturated fatty acids group, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are highly beneficial. They are often colloquially referred to as blood cleansers and brain gold, respectively. They possess important physiological functions. These include resisting inflammation, strengthening the brain, and improving concentration and memory. They also protect the health of the human nervous system and retina. The EPA content in the muscle of S. wangchiachii reaches 5.12%. This is significantly higher than that of S. prenanti (0.58%),15 M. piceus (1.34%),13 C. idella (2.97%),14 and Tortor sinensis (3.05%).20 Overall, the muscle of S. wangchiachii has a rich fatty acid composition with a high content of unsaturated fatty acids. In particular, the content of eicosapentaenoic acid (C20:5) is outstanding. Regarding fish size, the unsaturated fatty acid content in the muscle of medium-sized S. wangchiachii was slightly lower than that in the small size, but both were much higher than that in the large size. Furthermore, within the n-3 polyunsaturated fatty acids, the contents of α-linolenic acid (C18:3 n-3) and eicosapentaenoic acid (C20:5) in the medium-sized fish were significantly higher than those in both the small and large sizes.

4.4. Nutritional evaluation and comparison of mineral elements

Mineral elements are one of the six essential nutrients required for human growth and development. They are involved in building and repairing body tissues, regulating physiological metabolism, and enhancing immune function. They even play direct roles in preventing and treating diseases.22 The muscle of S. wangchiachii contains six trace elements and three major mineral elements. Among these, the content of the trace element zinc reaches a high level of 9.04 ± 0.20 mg/kg. It has been reported that biological antagonism occurs between elements with similar physicochemical properties. This antagonism happens when the zinc-to-copper ratio is greater than 10 or the zinc-to-iron ratio is greater than 1.23 In the muscle of S. wangchiachii, the zinc-to-copper (Zn/Cu) ratio was 9.13. This value is lower than the antagonistic threshold (10). The zinc-to-iron (Zn/Fe) ratio was 1.11, which is close to the critical threshold (1). These results indicate that the proportions of iron, zinc, and copper in the muscle are relatively balanced. Therefore, they are unlikely to cause strong antagonism of absorption. Statistics show that the average selenium content in the muscle of 33 freshwater fish species (e.g., C. carpio and C. auratus) is 0.81 mg/kg.24 In contrast, the muscle selenium content of S. wangchiachii in this study was significantly lower. It ranked near the bottom (32nd out of 34) when compared with these 33 species. Therefore, it is recommended to appropriately supplement selenium in the feed during future aquaculture practices.

5. Conclusion

In conclusion, the muscle of Schizothorax wangchiachii is a high-quality protein source with excellent nutritional value and strong umami flavor, characterized by high meat yield and crude protein content. It is rich in flavor amino acids and highly beneficial n-3 polyunsaturated fatty acids, particularly EPA. Nutritional profiles exhibit size-dependent dynamics: large fish possess more total and flavor amino acids, with tryptophan replacing valine as the first limiting amino acid. In contrast, small and medium-sized fish retain higher proportions of unsaturated fatty acids. Furthermore, while the muscle shows high zinc levels with balanced absorption ratios, its significantly low selenium content underscores the need for dietary selenium supplementation in future aquaculture practices.

Acknowledgments

This work was supported by the National Key Research and Development Program of China (Grant No. 2016YFE0102400) and the Independent Scientific Research Project of Yalong River Hydropower Development Company, Ltd. (Grant Nos. KY2019-05 and KY2019-23).

Authors’ Contribution - CRediT

Conceptualization: Longjun Deng, Tiancai Li; Methodology: Tiancai Li, Jianhua Liu, Dan Xu; Formal analysis and investigation: Tiancai Li, Dan Xu, Chengquan Xiang; Writing - original draft preparation: Tiancai Li; Writing - review and editing: Tiancai Li, Longjun Deng; Funding acquisition: Longjun Deng; Resources: Jianhua Liu, Chengquan Xiang, Longjun Deng; Supervision: Longjun Deng.

Ethical Conduct approval – IACUC

Throughout the trial, all efforts were made to minimize stress, discomfort, and suffering of Schizothorax wangchiachii. Fish were acclimated prior to experimentation, handled gently, monitored daily for health and welfare, and euthanized humanely following accepted aquaculture welfare standards. The research complies fully with the Convention on Biological Diversity and the Convention on the Trade in Endangered Species of Wild Fauna and Flora (CITES).

Data Availability Statement

All are available upon reasonable request.

Competing of Interest - Cope

No competing interests were disclosed.

All authors and institutions have confirmed this manuscript for publication.