Proximate composition and amino acid profile of European eel skin: influence of body weight

Abstract

Fish processing industries worldwide are discarding million kilograms of fish waste per year. The disposal of these wastes is an important handicap in fish processing industry. The thick eel skin is considered a waste product in the fish processing industry and in the home and is usually converted into low market-value products. The aims of this study were to evaluate the variations in the general chemical composition and amino acid content of eel skin in relation to body weight. The moisture content decreased and the lipid content increased with the weight of the eels. Eel skin had a high protein content, which did not vary significantly with eel weight. Glycine was the most abundant amino acid. The predominant essential amino acid was leucine. The smaller eels contained higher levels of threonine, valine, isoleucine, leucine, lysine, glutamic acid and tyrosine than the other groups. The larger eels contained higher levels of methionine, hydroxyproline, glycine, arginine, alanine and proline than the other groups. The protein indices showed that the skin from smaller eels was of higher nutritional quality. Graphical abstract

Cage culture of tropical eels, Anguilla bicolor pacifica and A. marmorata juveniles: Comparison of growth, feed utilization, biochemical composition and blood chemistry

“…In addition, the lower body moisture contents in A. marmorata reflect the inferior growth performance and feed efficiency of this species as reported in other eel species such as the Australian short‐finned eel A. australis australis fed on diets with plant and animal byproducts (Engin & Carter, 2005). The result is in contrast with the findings of Gómez‐Limia et al (2022), who reported that small eels have higher moisture content than adult conspecifics. On the other hand, higher whole‐body lipid contents observed in A. bicolor pacifica may be the consequence of feeding high lipid formulated eel diet.…”

“…Furthermore, it is noteworthy that both eel species must have accumulated high levels of glycine, which was also present at higher levels in the diet. Gómez‐Limia et al (2022) also detected elevated levels of glycine in European eel skin, indicating the presence of collagen.…”

“…On the other hand, higher whole‐body lipid contents observed in A. bicolor pacifica may be the consequence of feeding high lipid formulated eel diet. Eels tend to store lipids during growth and development for migration and survival (Gómez‐Limia et al, 2022; Luzzana et al, 2003). This suggests that slight differences in body lipid contents may also be related to eel size, which is in line with the study of Heinsbroek et al (2007), who suggested that body composition is strongly related to the body weight of A .…”

“…However, due to intense fishing pressure, there has been a dramatic decline in the wild population of temperate eel species especially the European eel A . anguilla , Japanese eel A. japonica and American eel A. rostrata (Gómez‐Limia et al, 2022; Tatsukawa, 2003), which are now categorized as ‘endangered’ by the International Union for Conservation of Nature Red List of Threatened Species (IUCN, 2019; Jacoby et al, 2014). This resulted in significant interest in other anguillid eel species from some Southeast Asian countries, particularly the Philippines as an alternative to cold water eel species (Cuvin‐Aralar et al, 2019; Muthmainnah et al, 2016).…”

“…Hence, eel farming is still highly dependent on wild seed stocks, which are collected from estuaries and tidal rivers during the migration of glass eels and young elvers to inland freshwater habitats (Liao et al, 2002). However, due to intense fishing pressure, there has been a dramatic decline in the wild population of temperate eel species especially the European eel A. anguilla, Japanese eel A. japonica and American eel A. rostrata (Gómez-Limia et al, 2022;Tatsukawa, 2003), which are now categorized as 'endangered' by the International Union for Conservation of Nature…”