**5. The role and importance of fatty acids in molluscs**

Lipids are major sources of metabolic energy and of essential materials for the formation of cell and tissue membranes, and they are important in the processes of egg productions. They are very important in the physiology and reproductive processes of marine animals and reflect the special biochemical and ecological conditions of the marine environment. Lipids also provide energy for growth during conditions of limited food supply, when carbohydrate levels (the main energetic reserve in molluscs) are low.

All compounds which are produced by molluscs are varied because of environmental factors such as temperature, salinity and seasonally variations. Therefore, changes in environmental factors could cause variations in the chemical components. Therefore differences in chemical components need different conditions for production, for example fatty acids and amino acids are related to specific temperature and salinity. In conclusion, environmental factor changes in different seasons could be caused in decrease or increase level of compounds. Also, other biological factors such as food availability, metabolic and physiological activities can affect

Amino acids are classified into essential amino acids (EAA) (cannot synthesized by humans) and non-essential amino acids (NEAA). In addition to oils and other hydrocarbon derivatives in the marine environment, the hydrocarbons synthesized by organisms occur normally in this environment. Aliphatic hydrocarbons are the principal group, and can occur in several

There are different type of fatty acids such as ∑SFA, ∑MUFA, and ∑PUFA in the whole body of molluscs. There could be changes or variations in their levels of different groups in the different seasons. These differences might be based on temperature, feeding habitats, or metabolic

The triacylglycerol compounds store SFAs for energy purposes in different processes in body and they also may be interim PUFAs reservoir, which could be transferred to the structural lipids or directed to specific metabolic routes for function of different organs. In contrast, phospholipid compounds fractions of mollusks show considerably less seasonal variations to maintain structural exactness of the cell as compared to the store of saturated fatty acids to be used as a source of energy and store of PUFAs required for phospholipid synthesis to multiple membrane structures or to be integrated in several metabolic processes [25, 26].

Molluscs are sources of many important and different natural compounds such as amino acids, fatty acids, lipids, terpenes and steroids. Different types of fatty acids such as lipids, ∑SFA, ∑MUFA, and ∑PUFA, omega 6 to omega 3 and other compounds are produced by different classes of molluscs specially polyplacophora, gastropoda, cephalopoda and bivalves. Four classes are important, that they could produce about 600 natural compounds. The level of natural compounds between different species, organ and sexes are different, and many of biotic and abiotic factors can cause variations in those levels. Also, the process and metabolism are different for all compounds. Finally, amino acids, lipids and fatty acids, terpenes and

Lipids are major sources of metabolic energy and of essential materials for the formation of cell and tissue membranes, and they are important in the processes of egg productions.

steroids are important natural compounds that they could be produced [27–29].

**5. The role and importance of fatty acids in molluscs**

the compounds such as lipid and fatty acids composition of molluscs [13–15].

**4. Different types of natural compounds in molluscs**

species of marine as well as terrestrial plants and animals.

demands [24–26].

236 Biological Resources of Water

The lipid composition can be affected by external (exogenous) factors, such as fluctuations in the environmental conditions and qualitative and/or quantitative changes in food availability, or by internal (endogenous) factors such as sexual maturation [28–30].

Accumulation and depletion of stored reserves in molluscs depends mainly on the stage of gonad development, environmental factors affecting metabolic activities and on the quantity and nutritional value of the food supply. Usually, the glycogen compound is the major energy source in species, while lipids are considered as the nutritive store source of the gonad organs. A high correlation between the gonad lipid content and the phase of the reproductive process cycle has been established in different species of bivalves and also prosobranch species.

Seasonal variations in lipid and fatty acid compositions have been reported for several marine molluscs and are generally related to the growth process and the maturation cycle: in the summer season and in the high temperature when the growth process takes place, receptacles of lipid compounds are build up and stored, and these are later consume for gametogenesis in the maturation cycle (often autumn or winter), normally are decreased during spawning process. However, the majority of these publications have focused on the class bivalve class, probably because of their major commercial importance and influence on the public health of people. Studies about biochemical compounds and their chemical structures, particularly fatty acid compounds in prosobranch gastropods, are strait [30].

Limpets are herbivore grazers which remove large quantities of unicellular microbes, algal germ lings and detritus, apparently unselectively, during feeding excursions around the home scar. As a consequence, there are considerable variations in their diets. There is a large amount of literature detailing about fatty acid compositions of a large number of species of marine algae. Availability and quality of algal lipids are very important in the nutrition, growth and development of aquatic animals such as marine fish larvae, shrimps and molluscs [28, 31, 32].

Molluscs phylum are of important aquatic invertebrates that the levels of the chemical compounds such as fatty acid components are higher in their tissues in comparison with other animals. They exhibit a range of lipid and fatty acid components in both freshwater and marine species and therefore fatty acid contents in mollusks are studied in many habitats, because of their importance in human's life. Among the marine invertebrates, the molluscs are the potential source of bioactive substances. The bioactive compounds isolated from the gastropods are considered to have a role in the chemical defense of the animals against their predators. Molluscs in the oceans are common sight and are virtually untapped resource for the discovery of novel compounds [27, 29].

Marine molluscs are excellent sources of nutritionally important compounds, such as fatty acids, amino acids and sterols. Fatty acids are essential for life, due to their key role as a good source of energy, membrane constituents, as well as metabolic and signaling mediators. In recent years, poly unsaturated fatty acids (PUFAs) have been recognized as a good remedy for cardiovascular diseases. Marine organisms consume diets rich in n-3 PUFAs and the lipids of the animals can contain up to 50% unsaturated fatty acids, with five or six double bonds, including 22:6 n-3 and 20:5 n-3 [18, 19].

Obesity disease which is a complex condition along with organs dysregulations and molecular pathways, such as adipose organ, liver, gastrointestinal tract, pancreas, central nervous system (CNS), and genetics. The role of the CNS in this disease needs more attention as obesity rates rise and relating treatments might fail. Since hypothalamus system has long been recognized in the regulation of appetite and food intake, the role of the CNS systems were examined as well as environmental impacts on energy balance. Furthermore, the omega-3 fatty acids have an important role in this disease and in the prevention and management of

Chemical Ecology of Biocompounds in Molluscs http://dx.doi.org/10.5772/intechopen.72741 239

The omega-6 and omega-3 polyunsaturated fatty acids (PUFAs) compounds are very important and essential fatty acids that must be derived from the diet compositions. Since omega-6 and omega-3 polyunsaturated fatty acids (PUFAs) compounds need endogenous enzymes for omega desaturation and there are no endogenous enzymes for omega desaturation in human and other mammals, these compounds cannot be made by man or other mammals and could be made particularly by Mollusca species. Modern agricultural western diets contain excessive concentrations of omega-6 PUFAs but very low concentrations of omega-3 PUFAs, leading to an unhealthy omega-6/omega-3 ratio of 20:1, instead of 1:1 proper for evolution process

Thus, an unbalanced omega-6/omega-3 ratio in favor of omega-6 PUFAs is highly prothrombotic and proinflammatory, which contributes to the prevalence of atherosclerosis, obesity, and diabetes. In fact, regular and balance of the omega-6/omega-3 ratio have positive effects for of these diseases and is the important factor for improve of these diseases (obesity, diabe-

As mentioned earlier, omega-6 to omega-3 fatty acids compounds cannot be made and convert in humans and other mammalian cells, therefore, they cannot made enzyme for omega-3 desaturase and so they lack converting enzyme, omega-3 desaturase. Omega-6 and omega-3 fatty acids compounds are not interconvertible, and they are metabolically compounds and functionally distinct. Also they have important opposing physiological influences, therefore, omega-6 to omega-3 fatty acids balance in the diet is very important for better function and body protection [6, 7]. When fish consume by humans or predators, the EPA and DHA from the diet composition partially replace the omega-6 fatty acids, especially AA, in the skin and membranes of almost all body cells, but specifically in the membranes of platelets, erythrocytes, neutrophils, monocytes, and liver cells. The parent compounds for eicosanoid formation, are AA and EPA fatty acids. Because of high levels of omega-6 in the diet, the eicosanoid metabolic products from AA, especially prostaglandins, thromboxane, leukotriene, hydroxyl fatty acids, and lipoids, are formed in larger amounts than those derived from omega-3 fatty acids, especially EPA [32]. The eicosanoids from AA are biologically active in very small concentrations and, if they are formed in high levels, they contribute to the formation of thrombus and atheroma; allergic and inflammatory disorders, particularly in susceptible people; and proliferation of cells. Thus, a diet composition rich in omega-6 fatty acids shifts the physiological state to prothrombotic, proinflammatory, and proaggregatory effects with increases in blood viscosity, vasospasm, and vasoconstriction and cell proliferation. Omega-6 and omega-3 fatty acids balance is a physiological state that is less inflammatory in terms of prostaglandin, gene expression and leukotriene metabolism activity, and interleukin-1 (IL-1) production [28–31].

obesity [3, 4, 6].

in the humans [9, 10].

tes, atherosclerosis and cancer) [23, 24, 26, 30].

The term sterol refers to a compound with a fused cyclopentano phenanthrene ring with a 3-hydroxyl moiety. Early studies of gastropod sterols indicated cholesterol as the principal sterol of all species. Most species only one or two types of sterols present. Amino acids are the building blocks of protein molecules. They cause metabolites in the homeostasis of an organisms, due to their role as the regulation of several cellular processes and also as precursors of other molecules, such as hormones and nitrogenous bases. Lipid compositions and storage strategy in molluscs, particularly of bivalves and gastropods, have been studied since lipids constitute a major fraction of molluscan tissues. Almost all the data included in their lipid studies, concern the entire organism and only a few reports on the tissue distribution of fatty acids are available [24, 26, 28, 29].

The lipid in the gill tissue in the marine molluscs has important role for regulate of ions such as Na. In the marine animals, the primary site of Na uptake is gills. In addition to being the initially site of an ion transport, gills also captive food, have roles in gas exchanges and act as a brooding chamber for the larval glochidia in females species. Thus, gills activate in many different functions, regarding that their related importance may vary during the year. From the lipids, C20:4ω6 acid is an active substrate for prostaglandin productions involved in regulating Na uptake and it has relatively high contents in gill lipids. Therefore, high level of C20:4ω6 acid in the gill is probably related to prostaglandin synthesizing in the gills to regulate Na uptake. Finally the accumulation of C20:4ω6 acid in the gills was related to physiological activities in the organs [22, 30–33].

Fatty acids are organic compounds consist of hydrocarbon chains with terminal carboxyl groups. The fatty acid chains in sea foods differ from vegetables in length. In the presence of Omega-3 fatty acids, prostaglandins actions on epinephrine is diminished and thus constriction or narrowing of blood vessels is prevented. Therefore, marine Mollusca have been regarded as a good source of lipid compounds, and lipids are proper energy sources for animals and nutritive foodstuff for human diets [34].
