Dried fish is a common and popular cuisine among the people of South and South-east Asia due to it’s unique taste and flavour. Dried fish can easily be stored, transported and can be available throughout the year (Hazrati et al., 2021). Drying can be recognised as a traditional method among the indigenous tribes (Ullah et al., 2016). Various research done on the nutritional aspect showed that the fish protein can be put alongside the ranks of chicken protein. However the likes of protein in the red meat or the egg albumen is lower compared to that of the fish protein (Srivastava, 1959; Ullah et al., 2016).
       
The North Eastern region of India is a home to several endemic fish species. Moreover, this region is blessed with ample rainfall, even the world’s wettest place- Mawsynram is located in this region.  With the onset of the monsoon period, fish catch of the season becomes ample. Locals often harvest large loads of fish, a considerable part of which is preserved via different drying practices) Sharma et al., (2013). The climate of Northeast India, being humid and subtropical, makes fish highly prone to immediate spoilage due to chemical and microbial activity or even due to autolysis. Moreover, the physiochemical parameters of the specific water body decides the health of the fish (Devi et al., 2024). Upon capture, fish are either cleaned and washed or directly dried using locally adapted methods employed by varied tribes and communities. All these preservation practices help in shaping the taste, quality and smell of the end product (Ullah et al., 2016). However, there can be other alternatives to fish, such as Azolla species, which also showed various concentration while undergoing different dried methods (Anokhi et al., 2026), but not widely consumed as compared to that of fish.
       
The Striped Dwarf Catfish, Mystus vittatus, (locally known as Tengra) is a commonly available and widely consumed freshwater fish species in the Barpeta region of Assam, India. Due to its smaller size, it can not only be dried, but used for making various fermented fish products like Napham which is consumed by the Bodo tribes of this region of Assam. Indigenous fishes are considered to have greater value and are available easily (Rifat et al., 2023). These are a good source of readily available protein, lipids and minerals. Drying fish like Mystus vittatus can lead to dehydration (Fitri et al., 2022) retaining the proteins and minerals. Among the various drying methods, the most common ones are sun-drying, kiln drying and smoke drying (Rana et al., 2025). Sun-drying method is widely applied technique used for drying fish. Being the most economical technique, it possess limitations as it is dependent upon the weather (Kamal et al., 2023; Rana et al. 2025). On the contrary, smoke drying technique can also be adopted. But due to the accumulation of harmful chemicals like carbon monoxide, carbon dioxide, polycyclic hydrocarbons (Okpala and Ekechi, 2014) etc., it cannot be considered as a safe alternative for sun-drying. Oven drying process is basically done in a closed environment free from microbes, pathogens and also it is weather independent (Abraha et al., 2018; Rana et al., 2025).
       
Dried fish is markedly important for economically disadvantaged sections (Jakhar et al., 2018), for whom dried fish represents the most affordable source of animal protein. Along with the potential nutritional value, it also adds up to it’s greater longevity and functions as a valuable source of essential fatty acids and minerals. Since the purchase and maintenance of freezing and other low temperature set up is beyond expensive for most small scale fisheries, unsold landings are typically preserve using traditional methods such a solar drying, kiln drying or smoking. According to research, about 40-50% of available freshwater fish is processed using the drying practices. Certain drawbacks are also unavoidable which includes insect infestation and accumulation of windborne sand (Afolabi et al., 1984).
       
In Assam, traditional methods of fish drying such as sun drying and smoke drying are widely practiced. Although studies are there on the different drying methods on fishes (Akinneye et al., 2010; Hei and Sarojnalini, 2012; Ogbonnaya and Shaba, 2019; Rana et al., 2025; Ullah et al., 2016), there is no any work performed on the effects of different drying methods on the nutritional content of Mystus vittaus. Therefore, the present study is undertaken to identify better applicable drying technique for retaining the nutritional quality of this fish species. Understanding its impacts will not only lead to improvements in drying techniques but also help the rural communities of this region to produce better quality dried fishes for ensuring food security and sustainable livelihoods.

Fish collection and processing
 
Sixteen fresh species of Mystus vittatus were taken from the local fish market of Barpeta, Assam, India. The study was conducted for a period of one year i.e. from  July 2024 to August 2025. These fish samples were uniformly distributed into equal numbers for all the different drying techniques to be conducted during this study i.e. as fresh fish, sun dried, smoked and electric dried respectively (Fig 2). Experiments were carried out in triplicate. All the proximate analysis have been carried out in the laboratory of Zoology department of Bhattadev University, Assam, India.
       
The fishes were washed properly and gutted well. They were then were dried without applying salt. The fishes were kept in open sunlight for three days and timely turned (every 5-6 hours) so that the fishes are dried uniformly. For the preparation of smoke-dried fish, the fish species were then placed in a wired net above burnt wood. The fishes were exposed to the smoke for about 5 hours. In between the new wood were burnt at regular interval inorder to maintain the concentration of the smoke. For the preparation of electric dried fish, the fish species were then taken in a petridish and kept in the oven for about 5 hours. The temperature was set to 70°C for the first hour and then reduced by 10°C in the completion of every one hour. Moreover the fishes were checked at proper intervals so that the fish donot get burnt. After the fish were properly dried, the head, fins, barbles and the scales were removed carefully. These were then turned into fine powder by the help of a grinder and separately kept in a plastic zip bag. The experimental design is schemetically explained in Fig 1.




 
Proximate analysis of Mystus vittatus
 
The fresh fish smaples were exposed to 60°C in a hot oven until a constant weight is obtained. The same process was applied for the dried fishes too. Since the dried fishes were already dried in the initial stage, they were exposed to further drying until a constant weight is achieved. The weight was measured in Wenser Company electric balance.
       
The moisture percentage was calculated by the following formula.

Ash contents were determined following the A.O.A.C (1997) standard procedure. The grounded/powdered samples were burned inside the muffle furnace, (Model: Relitech 2008 Certified Co.), at a temperature of 600°C for constant 2 hours. The ash content of the samples were then calculated by applying the following formula:

The protein concentration of the fish samples were estimated by the help of NanoDrop spectrophotometer. In this method, 1.5 gm of the powdered sample was taken in an eppendorf tube and to it 500 µl protein estimation buffer is added. The tube is then placed in vortex first and then the contents inside the tube was crushed by micropestle. The tube was the centrifuged at 8000 RPM for 10 minutes. The supernatent was taken for the estimation. First, 1 µl of the buffer is placed in the spectrophotometer for calibration and same amount of the supernatent was added  in the NanoDrop spectrophtometer.
       
The lipid content estimation of  the samples were done by the Bligh and Dyer method (Bligh and Dyer, 1959) (Can J Biochem. Physion. 37,922, 1959).    

The percentage of lipid concentration was calculated by the formula:

For carbohydrate estimation, Anthrone method (Ludwig and Goldberg, 1956) was followed. The concentration was obtained after plotting a graph of optical density against the standard curve of glucose. This concentration was calculated using the MS- Excel sheet.
 
Statistical analysis
 
The data obtained from various experiments were analysed using the Mean ± Standard error (SE). Bar graphs has been used to compare the biochemical parameters of the various processed fish. The data were analysed using ANOVA. The results were judged significant if p≤0.05.

Proximate composition
 
The proximate composition of the fresh fish and the dried fish were tabulated in Table 1. The moisture content ranged from 69.76±0.25% to 11.8±0.88% with fresh fish showing the highest content while electric dried fish with the least moisture content. The ash content of Mystus vittatus ranged from 4.2±0.28% to 9.97±0.91%. The highest ash content was seen in case of electric dried fish whereas the lowest was seen in case of fresh fish. The protein content ranged from 11.22±0.64 mg/mL to 17.78±0.22 mg/mL. Electric dried fish showed the highest concentration and fresh fish showed the least. The lipid content ranged from 8.17±0.61% to 27.88±0.83% with electric dried fish showing the highest lipid concentration and fresh fish showing the lowest. In case of carbohydrate content, the value were found to be minimal ranging from 0.41±0.04 mg/mL to 0.78±0.05 mg/mL with electric dried fish showing the highest among the four samples and fresh fish with the lowest value.


       
The p-values for all the parameters were found to be <0.05, thus indicating the differences to be statistically significant among the various drying methods i.e., smoke-drying, electric drying and sun-drying. The p-values for various samples are tabulated in Table 1.
       
Preservation is an efficient way to store fish, which is a highly perishable food, for a longer period of time. This technique not only fulfils the purpose of storage but also alter the nutritional concentration of the various macromolecules present in the fish which are a key dietary component in food. Presence of moisture determines the quality and health of the fish. Water harbours a number of microbes that can lead to the degradation of the fish when it is killed for food. A number of significant changes were seen in the moisture percentage of the fish. The current study showed that the electric dried fish was subjected to a greater loss in the moisture content compared to the smoke dried. Least reduction is seen in case of raw fish. As stated by Afolabi et al. (1984), the composition of the fish which were treated with various drying methods contributed to the decrease of water in the fish body (Afolabi et al., 1984). Castrillón et al. (1997) also observed that frying and heating resulted in the moisture loss in case of the sardines (Castrillón et al., 1997). Ali et al., (2011), also noticed a severe reduction in moisture when the fish were traditionally smoke dried (Ali et al., 2011).
       
Ash content highlights the total inorganic mineral and matter which remains after the burning the organic matter. A higher ash content oftens indicates a rich mineral percentage in the fish. In the present study, the ash content ranged from 4.2±0.28% to 9.97±0.91% where the fresh fish showed the lowest ash content, which was 4.2±0.28% and electric dried fish displayed the maximum value i.e. 9.97±0.91%. Smoke dried showed moderate value which was 5.78±0.68% and sun-dried was 8.38±0.4%. In the work carried out by Chukwu and Shaba (2009), it showed that while the protein, lipid and energy content were drastically affected by kiln smoking and oven drying, ash contents stayed almost the same (Ogbonnaya and Shaba, 2019). In on the contrary, Ali et al. (2011) observed and increase in the ash contents which the fish undergone smoking showed up to 9.86 g/100 g.
       
Protein is considered as the building block of the muscle. Protein is high in the meat and flesh of the fish. In the assessment conducted in this study, the protein concentration of the fish subjected to electric drying was the highest among the other drying methods. It was seen that protein content of the fresh fish was 11.22±0.64 mg/mL, smoke-dried fish was 14.15±0.42 mg/mL, sun-dried was 16.80±0.19 mg/mL and electric dried fish was found to be 17.78±0.22 mg/mL. Similar studies showed the differences in the concentration of the protein when it is subject to drying. Afolabi et al. (1984) found that the protein concentration of various fishes increased with the decrease in moisture (Afolabi et al., 1984). Similar studies were done by Raghunath et al. (1995) and found that drying Neripterus japonicus at a temperature about 50-70°C led minimized the solubility nature of the protein and denaturation (Raghunath et al., 1995). Moreover with similarity of the species of fish selected for this project, Mystus tengara had the highest protein concentration among the traditionally dried fish and smoked fish at Kawardha fish market (Jakhar et al., 2015) , a survey which was carried out by Jakhar et al. (2015); Agrawal et al. (2017) also showed that the protein content increased in smoke dried indigenous fish due to desiccation This indicated the process of smoking to be an effective technique of protein concentration.
       
Lipids are an important constituent of the cell cytoplasm. They are crucial for providing energy and essential fatty acids. In this present study, the lipid percentage of the electric dried fish was found out to be the highest where as the fresh fish was found to be the lowest. The lipid concentration was calculated for all the samples and the analysis indicated that the lipid content of the fresh fish was 8.17±0.61%, smoke-dried fish was 16.72±0.57%, sun-dried fish was 25.88±1.28% and electric dried fish was 27.88±0.83%. Castrillón et al. (1997) on their studies found that frying and successive heating of oil sardines lowered the PUFA and SFA, however an increase in MUFA is seen (Castrillón et al., 1997). Chukwu and Shaba (2009) highlighted that kiln smoke and oven drying immensely affected the lipid content in Catfish (Ogbonnaya and Shaba, 2019).
       
Carbohydrates are the basic composition of the protoplasm in the cells. It is considered as the storage and release of energy. Glucose, fructose, galactose etc. are the sources of carbohydrates in fish. In case of fresh fish, the carbohydrate content was found to be 0.41±0.04 mg/mL. For smoke-dried fish the carbohydrate concentration was found to be 0.65±0.05 mg/mL. For sun-dried and electric dried, it was 0.71±0.05% and 0.78±0.05% respectively.  Similarly Chukwu and Shaba (2009) showed the various concentration of carbohydrate when the fish was subjected to different drying methods (Ogbonnaya and Shaba, 2019). The result did not follow a single trend. It showed that the distribution of carbohydrate was not uniform. The untreated fish had the highest amount of carbohydrate compared to the processed fish. However carbohydrate was found in very low amounts compared to other macromolecules.

In the current scenario, global warming has become a common problem in each and every corner of the world. Fish being a readily available food for protein and other nutritional content is consumed by most of the people. Due to the gradual rise in temperature in present time, retaining the quality and taste of the fish has become a challenge. To tackle this issue, the fish are consumed without delay. However in the field of export, trade and commerce, preservation is the only way to keep the fish in a condition to be consumed.
       
Studying the various methods of drying of Mystus vittatus has several benefits, especially among low income and rural populations. Drying of fish is a traditional practice among the households, especially by women. Knowing the proper techniques and the value of such processed fish, can be a great source of income for these households.  However, it should be noticed that such practices are carried out in clean and hygiene conditions, as any negligence can lead to contamination of the fish and may result in adverse health crisis and ultimately economic loss.

The authors would like to acknowledge Biotech Park, Guwahati, Assam and the Department of Zoology, Bhattadev University, Bajali, Assam for providing us the necessary laboratory facilities for carrying out the work.
 
Author’s contribution
 
This work was carried out in collaboration among all the authors. All authors read and approved the final manuscript.

Authors have declared that no competing interests exist.