Why Hilsa is called “the king of fish”? The reasons behind unique tastiness of Hilsa

Hilsa is considered as one of the most tastiest fish due to its distinctly soft oily texture, mouthwatering flavour and superb mouthfeel. The fish is locally called “Macher Raja” means the king of fish.

The human tongue recognizes four basic tastes as sensory responses in different taste buds, viz., sweet, sour, salty and bitter (Keller, 1985). The sweet taste is sensed at the tip of the tongue, the salty taste at the tip and edges, the sour at the edges and the bitter at the deep back. Bitter sensation takes longer time to perceive and tends to linger. Flavour is perceived when volatile flavor compounds stimulate the olfactory fibers in nasal air passages. Mouthfeel occurs at a variety of nerve endings in the oral cavity. When tasting, human sensory organs perceive not only the four basic tastes, but also warm, cold, pain, tactile and pressure sensations. When food is taken into the mouth, all the sensations are usually recognized to verifying the degree of tastiness (Keller, 1985).

Konosu (1979) and Konosu and Yamaguchi (1982) reviewed the taste of fish and shellfishes and concluded that the flavor of fish are distributed to extremely great variety of flavor compounds that are variable according to species and biological conditions. The nucleus of taste and flavor in fish is constructed by the synergistic effects of glutamic acid and neocleotides along with sodium and chloride ions. The core flavor is enhanced by other taste active amino-acids, mainly taurine and arginine, and nucleotides and inorganic ions. Peptides, organic bases, organic acids and sugars are also responsible for characteristic taste of some fish species. Flavour volatiles, lipids, fatty acids and glycogen also play important role in producing overall flavor. Konosu and Yamaguchi (1985) found large amount of anserine in five species of Atlantic salmon, a great tasty fish, and suggested that anserine present in the muscle of salmon should play a significant role in its taste.

The unique taste of Hilsa has often been attributed to the presence of certain fatty acids like steareic acid, oleic acid and many poly unsaturated fatty acids (ω3, ω6 ), viz., lenoleic, lenoleneic, arachidonic, eicosapentanoeic and docosa-hexanoeic acids (Mohanty, et al. 2011; Nath and Banerjee, 2012; Madhushudhana Rao et al. 2012). It is very widely accepted hypothesis, but the correlation between the content of these fatty acids and the tastiness has not been studied. However, some clues are there that clearly defines a close linkage between the polyunsaturation of fatty acids and the taste of the fish. Hilsa is tastier just before the spawning than post-spawning or maturing stages. During pre-spawning time, lipid content in female Hilsa generally range from 16 to 22 percent (Mohanty et al. 2011; Madhushudhana Rao et al. 2012). Female Hilsa grows faster, becomes larger and more tastier than the male of same age group. Riverine Hilsa, specially those from the river Padma, are more tastier than marine ones. Several researchers claimed that a sub-stock of Hilsa exists in the Padma river, although many authors described Hilsa as a single stock in the regions shared by Bangladesh, India and Myanmar (BOLME, 2011). Ahmed et al. (2004) found very distinct genetic difference between Chandpur-Kuwakata and Cox’s Bazar population of Tenualosa ilisha. The sub-stock of the river Padma might have been rich with characteristic type of taste-active compounds those impart further taste to this river population.

The taste and flavor of many fish was sometimes depended on their food and feeding behaviour (Connell, 1975; Love, 1992). Planktonic mollusk, Spiratella helicinia fed by fish gives rise to an off-flavor in marine fish muscle, often described as “petrol” flavor. The larvae of Mytilus sp. give a bitter taste in herring (Connell, 1975). The texture, colour and flavour of fish flesh depend on food and feeding habits (Tangeras and Slinde, 1994). The nature of habitat where it lives also influences the taste of muscles (Huss, 1988). Tastes of cultured pungus, anabas, major carps, etc differ greatly from wild ones due to the type and quantity of supplemental feed administered. Farmed salmon are not as colourful due to astaxanthin deposition as the wild one and therefore receives low price in the market. Salmonids are not able to synthesize astaxanthin and depend on adequate supply through feed to obtain colour (Foss et al. 1987). Carps from lotic environment or from big reservoirs impart characteristic taste and color in flesh than carps of small confined water bodies. The unique taste of Hilsa was also believed to be attributed to the environment where it grazes or to the feed it takes. Hilsa of freshwater origin is tastier than those of the sea. Godavari Hilsa was found to be testier than marine Hilsa in Indian waters of the Bay of Bengal (Madhushudhana Rao et al. 2012). During its time at sea Hilsa remains short, thin and less tasty but when it enters in freshwater its taste and growth increases. Hilsa feed on plankton, mainly blue green algae, diatoms copepods, cladocera, rotifer, organic detritus, mud, sand, etc. (Hora and Nair, 1940). The stomach of spawning Hilsa was found to contain a considerable amount of mud and sand also (Pillay, 1958). Hilsa filters planktons but also grubs on muddy bottom in the sea and brackish water environment (Madhushudhana Rao, et al. 2012). But it does not feed at all or takes less feed during its further upward migration from brackish waters (Pillay, 1964). During migration it is sustained by the accumulated fat in its body. Therefore, fat content decreased from the sea to the brackish water, then further to the rivers. Fatter Hilsa migrates faster and losses fats prompter in the rivers. Comparatively lesser fats in the river than their accumulation in the marine environment makes the flesh more soft and relaxed. During low salinity directed spawning migration, saturated fatty acids (depot fat) are converted first into mono- and then into poly unsaturated fatty acids. More the upward migration towards zero salinity, more the conversion into polyunsaturation was observed in many migratory fish like, Hilsa, Atlantic salmon, chum salmon and sockeye salmon (Jonsson et al. 1997; Magnoni et al. 2006; Sasaki et al. 1989). Probably more the poly unsaturation in fish lipid, more the development of characteristic texture and pleasant flavour in the muscles. Probably, that is why abdominal part is tastier than the dorsal, where both lipid content and level of unsaturation are higher (Salam et al. 2005; Shamim et al. 2011). Polyunsaturated fatty acid content was found to be lowest of 11.41% in marine Hilsa and highest of 26.87% in freshwater Hilsa (Madhushudhana Rao et al. 2012). Therefore, the transformation of saturated and mono unsaturated fatty acids into poly-unsaturated fatty acids are believed to be the key important phenomena that controls the unique taste of freshwater Hilsa. More over, among the PUFA, the quantity of docosa-hexaenoic acid (DHA, C22: 6ω3) was found to be 5.4 times higher than eicosa-pentaenoic acid (EPA, C20:5ω3) content in Godavari river Hilsa, while they were in smaller quantity in brackish water Hilsa. In the sweet-water environment, due to changed osmotic balance from the 30-35 ppt salinity to almost zero salinity, fish takes more water through mouth, gills and skin to produce and expel large volume of urine. Thus the musculatory system of the fish gets relaxed, muscle cells become soft and flexible and the fat-protein inter molecular adjustment becomes more comfortable. As the fish swims up the river, it flexes it muscles, leading to loss of body fat and makes herself more tasty (Mondal, 2012). The PUFA acts as the integral components of the cell membrane during the new osmotic balance in sweet-water system, the conversion of which is necessary to counter the changes in salinity of water during migration. On the other hand, as the fish does not take food or take less food while in the rivers, most of the off-flavours imparted in the muscles from the food and mud in marine/brackish water habitat are eliminated through continuous dialysis by the sweet water threshold. All these impart unique taste and flavour in the Hilsa muscles and make it the “Macher Raja” – the king of fish.

Reference:

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