Nutrient composition of fish, collected from wild and culture, is greatly varied in general. Because in intensive culture, fish are provided with nutrient dense compounded feeds that enables them to deposit large reserves of nutrients, in particular lipids. In contrast, considerable changes occurred in environmental condition fluctuates the availability and composition food that would affect the nutrient composition of wild fish20. In addition to food/feed, Piggott and Tucker21 listed some other factors influencing the nutrient composition of fish such as species, genetics, size, reproductive status and environmental characteristics. In our study, the moisture content of wild fish was observed to be the highest compared to the cultured ones and was drastically reduced with increasing body size. This result is in agreement with the findings of Alasalvar et al2, who found higher moisture content in the wild caught sea bass than the cultured fish. In the present study, muscle protein content of M. cephalus did not vary between the resources. Similarly, size variation had no effect on the protein level. This result is corroborated with the finding of Nettlon and Exler22 in channel catfish, coho salmon and rainbow trout. In contrast, a slight variation in protein content was observed between wild and cultured yellow perch17. The difference in protein content might be due to the variation in environmental conditions, species, size, sex of the individual animals and their reproductive status14.
In the present study, the muscle tissue of the cultured M. cephalus contained higher lipid content than the wild caught fish. This is in agreement with earlier reports that have shown that the level of lipid tend to be lower in fish collected from wild compared to cultured individuals of the same species, such as yellow perch17, turbot23, sea bream24, and silver pomfret25. The difference in muscle lipid content is most likely due to the result of dietary differences17. Grigorakis et al26 stated that the higher energy consumption would also be a reason for the storage of high lipid in cultured fish than the wild ones. The reduced activity of cultured fish than the wild fish would also influence the body lipid2. In addition, possible periods of starvation that encountered by wild fish might lead to reduce the lipid content of their body, which is not much occurred with cultured fish27. Morishita et al15 observed a higher muscle lipid content in cultured sea bream with increasing body weight and the same is corroborated in the present investigation, indicating that this as an intrinsic physiological trait. Rheman et al28 suggested that this would also be related to reproductive physiology of the fish. A similar observation has been made in sea bass29 (Poli et al., 2001). But in contrast, Giogios et al30 observed a lower lipid with higher body size and a higher lipid with a lower body size of cultured meagre fish. This difference would be attributed to a variation in lipid metabolism and feed offered during the culture. In most of the earlier studies2,17,23,24, an inverse relationship was observed between the moisture and lipid content, while Zhao et al25 did not find the same relationship in silver pomfret and stated that this might be because of silver pomfret is a non-fatty fish and the sample tested by the authors was originated by pooling five fishes together. Though, M. cephalus, used in the present study, is also considered as a non-fatty fish and though the analysis was done by pooling six fishes together in the present investigation, still observed an inverse relationship. Total ash content was significantly higher in wild fish compared to the cultured fish and is corroborated with our earlier findings9,14. In contrast, Alasalvar et al2 and Sharma et al31 reported no significant difference in ash content of sea bass and rohu, respectively sourced from culture and wild. The gross energy content was greatly varied between the sources (110.12-133.03 Kcal/100 g) and size groups (107.46-145.27 Kcal/100 g), which mainly related to the lipid content of fish as evidenced in the present study by a direct correlation between lipid and energy (Table 1).
It is essential to have adequate knowledge on amino acid content of fish protein to establish its nutritional value, as the nutritional quality of protein is mainly depending on EAA. Fish protein has a greater satiety effect than other animal proteins like chicken, beef, etc., with cheaper price7. The depicted values of amino acids in the present study was almost resembled to those presented by Mai et al32, who compared the amino acid composition of different fin-fishes, like white sucker, burbot, black crappie, rainbow trout, walleye pike and yellow perch. Of all the EAA, leucine found to be high and was in the range of 1.57–1.64% (wet weight basis). Etzel33 documented that leucine is mainly responsible for muscle protein synthesis and later, its therapeutic effect in various stress conditions of burn, trauma and sepsis is reported by De Bandt and Cynober34. Followed by leucine, M. cephalus had higher content of lysine (1.50–1.55% wet weight basis) and is agreed by Zhao et al25 in Pomfret. Iqtidar et al35 reported that lysine is one of the most limiting amino acids in cereal-based diets given to children and is extensively required for optimal growth, hence it is suggested fish as an optimal supplement for cereal-based diets. Methionine plays a vital role in treating Parkinson’s disease, liver disorder and schizophrenia, which would also help in the treatment of alcoholism, allergies, asthma, drug withdrawal, poisoning, particularly eliminating copper, radiation side effects, etc.,14 and was ranged from 0.74–0.81% in M. cephalus. Arginine was the second highest EAA in the muscle portion of M. cephalus, which is mainly considered as a precursor for the biological synthesis of nitric acid and play an important role in neurotransmission, blood clotting and blood pressure maintenance. The disease of sepsis, preeclampsia, erectile dysfunction and anxiety was much recovered with the supplementation of arginine. Isoleucine, phenylalanine, threonine and valine had a variety of roles in human nutrition mainly in chronic renal failure and nervous system disorders26 and were found to be around 1% in both wild and cultured M. cephalus. Liao et al37 documented the necessity of histidine in the growth and repair of tissues, myelin sheaths maintenance and to remove heavy metals from the body. Similarly, tryptophan acts as a precursor for different neurotransmitters like serotonin, dopamine and nor-dopamine and was in the range of 0.28–0.29% in our study.
Though NAA are synthesized de nova, they would also play a crucial role metabolically as in EAAs, especially in the regulatory process of gene expression, micro-RNA levels, metabolism, innate and cell mediated response38. Deutz et al39 reported that during critical illness, the effluxed glutamic acid from muscle serves as an important carrier of nitrogen as ammonia in the splanchnic area and immune system, which alone contributed more than 30% in total of NAA in our study. However, no significant difference was observed in muscle composition of both EAA and NAA, indicating that the protein content in M. cephalus was well balanced in amino acid composition, in particular EAA and is of high quality, irrespective of the resources and size. This result is corroborated with the findings of Gonzalez et al17 for the EAA content of wild and cultured yellow perch, but not for NAA and who reported significantly higher values for alanine, serine and tyrosine in wild caught yellow perch. Contrary, Zhao et al25 reported significant differences for all the EAA except arginine between wild and cultured silver pomfret and who found lower values in cultured fish than the wild ones. In relation to identifying the quality of protein, most of the studies are restricted in analysing only EAA. But in the present study, IP level was computed based on the FAO/WHO/UNU19 recommended values to elucidate that M. cephalus is how far better in providing protein/amino acid content in the human diet. It was found that IP level for all the calculated EAA was higher in M. cephalus compared to the recommended values except valine, indicating that M. cephalus is of good source in providing protein/amino acids irrespective of the resources even at varying size. Sarma et al40 found a marginal decrease in the IP value for histidine, leucine and threonine in golden mahseer, common snow trout and common carp, respectively as compared with the recommended level. Though the IP level of valine reduced than the recommended level in our study, the calculated EAAI has shown no significant difference among the EAA, including valine in both wild and cultured fish and also showed a positive correlation for EAAI between cultured and wild caught M. cephalus.
As a source of membrane constituents, energy, metabolic and signaling mediators, fatty acids, particularly n-3 PUFAs are recognized as essential nutrients for life. Aquatic species, primarily fish are generally characterized by high level of n-3 PUFAs, however, its composition influenced by many intrinsic and extrinsic factors. In our study, the level of saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) was significantly high in cultured M. cephalus than in wild caught fish, while the reverse was true for PUFA except C18:2c and γC18:3 and as reflected in n-6/n-3 ratio, which shown that significantly lower n-6/n-3 ratio in wild compared to cultured fish, indicating that marine environment would have an excellent source for n-3 rich foods and which might be lower in intensive culture system. This result is greatly in agreement with those previously reported by Zhao et al4. In contrast, Alasalvar et al2 found the reverse trend in sea bass, who reported about 29.2 and 33.4% of SFA in cultured and wild collected sea bass and the remaining quantity was shared by MUFA and PUFA. But in the present study, SFA was about 50.7% in cultured fish and almost similar level was observed for wild fish (49.6%). C16:0 was about > 70% of the total SFA content of both cultured and wild M. cephalus and was significantly higher in cultured than in wild fish, which might be attributed to the usage of supplementary feed containing higher C16:0. Similar results have also been reported in sea bass2, crappie16, rohu31 and sturgeon41. In MUFA, C18:1 was found as a major one in the both the fish and was significantly higher in cultured fish than that of wild ones. Similarly, C18:2c found to be ten-times higher in cultured M. cephalus compared to its wild counterpart, which is due to its dominance in compounded feed used for intensive culture26. Among n-3 series, both EPA and DHA had no much variation like other fatty acids between the wild caught and cultured fish, indicating that both the fish are of good sources for these fatty acids. However, a marginal increase was noticed in wild fish than the cultured ones, but the difference was insignificant for DHA. A great variation was noticed in C20:4 and was much higher in wild fish (170.36 mg/100 g) than in cultured ones (60.44 mg/100 g). A similar result was found by Gonzalez et al17 in yellow perch and who suggested that this might be due to the dietary effect and saturation and/or elongation mechanisms. Similarly, the highest concentration of αC18:3 was observed in wild fish than in culture, which could be attributed to the type of food, in which M. cephalus is exposed in the wild such as insect larvae, algae, crustacean that are rich in αC18:342.
Simopoulos8 documented that the ratio of 1–2:1 for n-6/n-3 fatty acids is being considered as an ideal level for beneficial health, while the Department of Health of United Kingdom recommends that this level might be up to 4:1. Whereas the Western diets provide n-6/n-3 ratio of around 15–25:1, which would be a reason for occurring various common health disorders like coronary heart disease and cancer. McDanniel et al43 suggested an approach, whereby consuming a higher dietary quantity of n-3 PUFAs, in particular C20:5 and C22:6 would be helpful in normalizing n-6/n-3 ratio. In our study, this ratio was 2.21:1 in cultured fish and was significantly low in wild caught fish (0.76:1), while it was in the range of 1.35–1.81:1 among the fish containing different body weight. All the values in our study were within the recommended values, indicating that M. cephalus could be considered as an optimal food source. Similarly, the DHA/EPA ratio seems to be lower in wild caught fish compared to cultured fish and the same was found in halibut fish44, sea bream45 and cat fish and tilapia46. In our study, all the fatty acids were gradually increased with increasing body size. However, the rate of increasing was not same among all the size groups. The proportion of the increase was almost similar between 100–150 g and 151–250 g groups as well as between 151–250 g and 250–500 g groups, while the increase was almost doubled in the fish categorized under > 500 g. The similar variations in fatty acids in relation to fish size have been reported in gold-spot mullet14, rainbow trout47 and gilthead sea bream48. Kiessling and Kiessling49 suggested that the relative variations on fatty acid composition with varied body weights could be attributed to the selective aerobic phosphorylation of fatty acids into the mitochondria of muscle tissue. The selective mobilisation of fatty acids to the reproductive organs in larger fish would also be a reason for the same50. In contrast, Ghomi and Nikoo51 observed higher level for C18:1, C18:2 and C18:3 in small size fish of sturgeon roe than the larger one.
Mineral content of fish is influenced by both diet and environment, especially in intensive culture and would also have an influence on flavor. In addition, deficiency of essential minerals in the diet might lead to improper enzyme-mediated metabolic functions, organ malfunctions and chronic disease. In our study, all the macro elements differed among the treatments except magnesium. Wild caught M. cephalus contained higher level of calcium, phosphorus, sodium and potassium than the cultured fish, while no significant difference was noticed for magnesium. Contrary, Gonzalez et al17 reported a higher concentration of magnesium, phosphorus, calcium and potassium in cultured yellow perch than that of its wild counterpart and the reverse was true for sodium. Whereas, micro elements were not affected except for iron. This result is agreed by Alasalvar et al2 in sea bass, however, a higher level of zinc was reported in cultured eel52. A linear relationship was observed in macro elements against fish body weight. Environmental conditions like water chemistry, salinity, temperature and contaminants would also responsible for the change in mineral composition2. Indian Council of Medical Research farms a simple recommended daily allowance guideline based on the FAO/WHO/UNU19 guideline to calculate the daily value (DV%) of food. Dayal et al53 reported that food with > 70% DV rated as outstanding and those had 50–70, 25–50, 10–25% are categorized as excellent, very good and good, respectively, while if it falls < 10% is considered as poor. According to this, lysine, methionine, threonine, tryptophan and EPA + DHA were considered as outstanding nutrients in both wild and cultured M. cephalus. Similarly, isoleucine, leucine, phenylalanine and valine were grouped under the excellent category. Protein, phosphorus and selenium were categorized as very good. A similar trend was noticed among the size groups. Cultured M. cephalus contained a higher DV for lipid, phenylalanine, threonine, tryptophan, valine and n-3 + n-6 fatty acids, whereas protein, cysteine, leucine, lysine, methionine, EPA + DHA, phosphorus and selenium were high in wild caught M. cephalus.
In conclusion, muscle of both cultured and wild M. cephalus is of good sources of protein with balanced amino acids, in particular EAA irrespective of the size groups. However, an important difference is found in some of the quality of lipid, fatty acid and macro mineral composition and they are influenced by both resources and size. In addition, the results of the present study indicate that M. cephalus contains higher ideal protein compared to FAO/WHO/UNU recommended level with a good daily value for most of the nutrients. Our results suggest that despite of the changes in nutrient content, both wild and cultured M. cephalus fall under the category of nutrient rich fish and would be an effective and healthy food material.