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 Table of Contents  
Year : 2016  |  Volume : 2  |  Issue : 2  |  Page : 50-55

New Approaches for the Effective Utilization of Fish Skin Wastes of Aluterus monoceros

1 Biological Materials Lab, CSIR-Central Leather Research Institute, Chennai, Tamil Nadu, India
2 School of Electricals and Electronics Department, VIT University, Chennai, Tamil Nadu, India
3 Department of Textile Technology, Anna University, Chennai, Tamil Nadu, India

Date of Web Publication29-Sep-2016

Correspondence Address:
Dr. Rethinam Senthil
Biological Materials Lab, CSIR-CLRI, Adyar, Chennai - 600 020, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2423-7752.191400

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Context: Unicorn leatherjacket (Aluterus monoceros) is an export quality fish mainly used for fillet production, the skin of which is discarded as waste due to its toughness. Wastes emanated from the fish processing industry have become an important source of environmental pollution. Aim: The study investigates the potentials of A. monoceros skin to produce value-added products viz., fish leather and fish meal. Materials and Methods: 5 kg of fish skin from 20 kg of fish was used for the present study. Leather produced from fish skin was characterized for its physico-chemical properties using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), etc. Biochemical components viz., protein, fat, and salt content of the fish skin were also estimated. Results: Leather produced from fish skin possessed 88 MPa tensile strength. Biochemical estimations proved that the fish skin had 28% protein content. Conclusion: On the basis of the characterization and evaluation results, it could be concluded that this processed fish skin could be used for leather goods production. In addition, this fish skin could be included as a component in fish meal preparation.

Keywords: Aluterus monoceros, fish leather, fish meal, fish skin waste, unicorn leatherjacket

How to cite this article:
Senthil R, Vedakumari SW, Hemalatha T, Sumathi V, Gobi N, Sastry TP. New Approaches for the Effective Utilization of Fish Skin Wastes of Aluterus monoceros. J Earth Environ Health Sci 2016;2:50-5

How to cite this URL:
Senthil R, Vedakumari SW, Hemalatha T, Sumathi V, Gobi N, Sastry TP. New Approaches for the Effective Utilization of Fish Skin Wastes of Aluterus monoceros. J Earth Environ Health Sci [serial online] 2016 [cited 2024 Mar 3];2:50-5. Available from: https://www.ijeehs.org/text.asp?2016/2/2/50/191400

  Introduction Top

Unicorn leatherjacket (Aluterus monoceros), commonly referred as file fish, is one of the most important salt water fish captured in Indian coastal area. It is a reef-associated subtropical fish occurring in the continental shelf down to 50 m depth and belongs to the family Monacanthidae and the order Tetraodontiformes. It is widely distributed in Atlantic, Indian, and Pacific oceans.[1] Fish size of A. monoceros ranges from 47 to 59 cm in length and from 0.75 to 1.3 kg in weight.[2] A. monoceros have a highly compressed body and the body is covered with rough textured scales. This species is used for fillet production and a large amount of skin is produced as fish processing waste. In addition, the skin of A. monoceros is very tough and elastic in nature.[3] Approximately 40.8 tonnes of skin is being discarded as waste in Tamil Nadu, India per year.[4] Value-added products produced from this fish skin would be an economical way of waste utilization.

The recovery of chemical components from seafood waste materials, which can be used in other segments of food industry, is a promising area of research.[5] Fish harvesters and processors want to maximize profitability and fish value by developing markets for fish by-products and reduce disposal costs.[6] A large use of fish processing wastes is in the production of poultry and animal feeds. There are chemical and biochemical differences between fish species which translates into species differences in the composition of fish waste components and by-products.[7] Treated fish waste has found many applications among which the most important are animal feed,[8] biodiesel/biogas,[9] dietetic products (chitosan), natural pigments (post-extraction), food-packaging applications (chitosan),[10] cosmetics (collagen),[11] enzyme isolation,[12] soil fertilizer,[13] moisture maintenance in foods (hydrolysates),[14] etc.

Development of leather from fish skin is yet another unexplored area of promising research. Fish skins are gaining interest among tanners as an additional source of raw material for making leathers due to their attractive and unique grain structure possessing high market value.[15] Collagen is a major structural connective tissue protein and various authors demonstrate the extraction of collagen from skin of file fish.[16] Since the skin of A. monoceros contains 22% collagen,[3] it presents unique opportunity for leather production. Karthikeyan et al.[17] have reported that leather produced from skin of stingray (Dasyatis pastinaca) provide acupressure effects when used as insole material.

Large yields of fish skin waste from A. monoceros in sizeable quantities provide good scope for leather production as well as for the preparation of value-added products. Hence, the main objective of this study is to prepare leather from skin of A. monoceros by tanning process and to analyze the feasibility of using skin as a component of fish meal. The product was characterized for its physico-chemical properties using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), energy dispersive spectrum (EDX), and scanning electron microscopy (SEM). Mechanical properties such as tensile strength, elongation at break, and tearing strength were also assessed. Biochemical components viz., protein, fat, and salt content of the fish skin were also estimated.

  Materials and Methods Top

All chemicals were obtained from Sigma and used as such.

Preparation of fish skin

Skin of file fish (A. monoceros) was obtained from Nagapattinam Harbour, Tamil Nadu, India in two batches. 5 kg of fresh skin obtained from 20 fish, each measuring 40–50 cm in length and 15–20 cm in width, was cleaned well with water, placed in polythene bag, immediately frozen, and stored at −20°C until use. The storage time was less than three months. A large number of variables can affect the composition of whole fish and its components including, fish size, time of harvest, gender, and other environmental factors.[18]

Fish leather preparation

Fish skins were obtained immediately following fillet weighing and based on the weight, water quantities were set for tanning process. In chrome tanning process, both mechanic and static methods were used. The skin was converted into leather after the following processes viz., liming, pickling, chrome tanning, neutralization, retanning, and polishing.[19],[20] Final surface finish of chrome tanned fish leathers was done using binders and pigments. Designing of finished leathers was done by plating.

Physical characterization

FTIR measurements were performed to determine the functional groups on the skin and prepared leather. The spectrum was measured at a resolution of 4 cm−1 in the frequency range of 4000–500 cm−1 using Nicolet 360 FTIR Spectrometer. TGA was used to analyze the thermal stability of skin and prepared leather. TGA measurements were performed using a TA Instruments High Resolution 2950 TGA thermogravimetric analyzer. Samples weighing between 10 and 20 mg were placed in a platinum pan and tests were performed in a programmed temperature range of 0–800°C at a heating rate of 5°C/min under nitrogen atmosphere at flow rate of 50 ml/min. Surface morphology of the samples was visualized by scanning electron microscope (SEM; Model LEICA Stereoscan 440). The samples were coated with gold ions using an ion coater (Fisons Sputter Coater) 0.1 Torr pressure, 20 mA current, and 70 s coating time, using a 15 kV accelerating voltage. The samples for physical testing were cut from the tanned leathers. Fish leather was subjected to various physical tests as per the standard methods (IUP).[21] Mechanical properties were analyzed using specimens of 4 mm wide and 10 mm length. Tensile strength (MPa), elongation at break (%), and tear strength were measured using INSTRON (model 1405) at an extension rate of 5 mm/min.


Samples of 1 cm2 were cut from skin and tanned leather and fixed in 10% neutral buffered (phosphate buffer solution) formalin for histological examination. Sections of 4 μm were obtained using microtome after embedding in paraffin block and mounted on glass slides and Van Gieson staining[22] was done.

Characterization of fish skin

Moisture content

The moisture content of the raw fish skins was determined according to AOAC.[23] Briefly, pre-weighed (Wi) skin samples were heated in a hot air oven at 110°C for 30 min. They were allowed to cool and then the weight of the dried sample (Wf) was recorded.

Ash content

Ash content of fish skin was calculated according to AOAC.[23] 0.001 kg of fish skin was placed into previously ignited, cooled, and tarred crucible. The samples were heated in a muffle furnace preheated at 600°C for 6 h. The crucibles were allowed to cool in the furnace up to 200°C and then placed into desiccators with a vented top. They were allowed to cool and then the residue (ash content) was weighed.

Biochemical estimation

The crushed fish skin of A. monoceros was washed thoroughly in distilled water. The washed skins were demineralized using 1 N HCl, for 7 days at 4°C. Later, the pH was elevated to 7 and the material was crushed to paste form, and the obtained paste was stored at 4°C till further use. Protein content and fat content of fish skin were estimated according to Lowry et al.[24] and AOAC methods,[25] respectively. Salt levels were analyzed according to Helrich.[26]

  Results Top

Fish leather

Fish leather had a smooth texture and it was elastic in nature [Figure 1].
Figure 1: Photography image of fish leather

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Physical characterization

FTIR spectroscopy was used to study the functional groups of the samples. Fish skin [Figure 2]a showed the presence of characteristic amide A, I, II, and III bands at 2926, 1651, 1432, and 1034 cm−1, respectively. In fish leather [Figure 2]b, peak areas were obtained around 3300 cm−1. In addition, the amide band at 1651 cm−1 in fish skin disappeared and a new amide band at 1569 cm−1 was observed.
Figure 2: FTIR (a) fish skin and (b) fish leather

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TGA was performed to study the thermal stability of the samples. Fish skin [Figure 3]a showed two-step weight loss, with initial weight loss of about 9% at 93°C, second weight loss of about 20% at 424°C, and 58% remained as final residue. Similarly, fish leather [Figure 3]b showed two-step weight loss with initial weight loss of about 13% at 95°C, second weight loss of about 33% at 383°C, and 25% remained as final residue.
Figure 3: TGA (a) fish skin and (b) fish leather

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Surface morphology of A. monoceros skin [Figure 4]a and leather [Figure 4]b was revealed by scanning electron microscopy. It was confirmed from the micrograph that tanning operation has improved fiber opening in the final leather.
Figure 4: SEM image (a) fish skin and (b) fish leather (500× magnification)

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EDX spectrum of fish skin [Figure 5]a and fish leather [Figure 5]b revealed the difference in elemental composition. From the EDX spectrum, it was confirmed that elements viz., calcium, silicon, and magnesium were concentrated more on the skin surface, whereas calcium was totally removed in the final leather. The fish leather possessed tensile strength of about 88.62 ± 3.05 MPa, 81.28 ± 8.05% elongation at break, and 54.38 ± 0.46 N/mm as tear strength.
Figure 5: EDX (a) fish skin and (b) fish leather

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Van Gieson staining was done to identify the changes in collagen structure [Figure 6]a and [Figure 6]b. The study revealed the opening up of fiber structure in the final leather compared to A. monoceros skin.
Figure 6: Van Gieson staining (a) fish skin and (b) fish leather

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Characterization of fish skin

The biochemical profile of A. monoceros skin was estimated, to assess its suitability for fish meal. Fish skin of A. monoceros possessed 9.6 ± 0.77% moisture content and 20 ± 1.34% ash content. Biochemical estimations revealed that the skin contained 27.8 ± 2.21% protein, 5.6 ± 0.6% fat, and 0.57 ± 0.1% salt, in addition to good amount of calcium.

  Discussion Top

Fish skin of A. monoceros was collected in various batches during its high catch period (September–December). There was not much difference in the leather produced using different batches, which proved to be a promising character for leather production. FTIR results revealed the formation of hydrogen bonds due to tanning in fish leather, which was responsible for its stability. Two-stage weight loss was encountered in TGA. The initial weight loss was due to the evaporation of water molecules in the samples. The second weight loss was due to the denaturation of proteins present in fish skin and fish skin leather, respectively.[27] The difference in residue at the end could be attributed to the loss of calcium in tanned leather. Isolated collagen fibers were visible in SEM, which could be attributed to fat liquoring.[28] EDX spectrum revealed the difference caused in fish leather due to tanning operations. Calcium was totally removed in fish leather due to tanning.[15] Mechanical properties of fish leather were higher when compared to the tensile strength (38 MPa) and elongation at break (65%) of sheep leather.Van Gieson staining revealed thick collagen fibers in fish leather, which could be attributed to tanning operations that removed the non-collagenous proteins.[18] Fish meal containing 50–60% protein, 10–12% fat, 7–10% moisture, >2% salt, and 22–25% ash is usually recommended for poultry feed, aqua feed, etc.[29],[30] The presence of essential nutrients in fish skin revealed its potentiality to be used in animal feeds.

Different leather products could be produced from fish leather owing to its physical and chemical properties. The fish leather obtained was of good quality and it had a smooth finish. It was clearly evident from the results, that fish leather possessed better mechanical properties, which may find applications in the manufacture of leather goods. Nowadays, the use of food wastes as animal feed is of high interest, because it stands for environmental and public benefit besides reducing the cost of animal production.[30],[31] Offal from the fishing industry could be used as a feed ingredient, as it represents a valuable source of high-quality protein and energy.[21] When regular leather costs around 4–6 USD per sheet (3 ft × 2 ft), leather produced using fish skin could be sold at 2–3 USD per sheet, since the raw material used for the preparation is relatively cheap. Nevertheless, since the results of the study were promising, future studies could be aimed at conducting studies on a large scale.

  Conclusion Top

Skin of A. monoceros was converted into leather by standard tanning protocols and the finished leather was characterized for its physio-chemical, histological, and mechanical properties. The mechanical properties clearly promise its use for the production of leather goods items. The biochemical profile of A. monoceros skin also reveals its use for fish meal production. Hence, the study has deciphered a methodology for fish leather production, a waste to wealth conversion, in addition to environmental pollution reduction.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

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