Plastic Metabolism

Fish species that differ in their physical activity also differ considerably in their level of plastic metabolism. Plastic metabolism is the metabolism of the whole organism, the sum of all activities, including the type of food consumed, the transformation of its basic constituents in the organism and the catabolic products excreted. 

Lipids are of special concern in comparing plastic metabolism between the two groups of fish. Triacyl-glycerols, cholesterol ethers and non-esterified fatty acids, which are the direct sources of energy, have already been discussed in the previous section. We now turn to phospholipids and cholesterol, which are essential to the structure of cell membranes, and to polyunsaturated fatty acids, which determine to a large extent the functional activity of these membranes. 

In Chapter 2, section 2.1, the importance of lipids in temperature adaptation was noted, and the versatile role of phospholipids, cholesterol and polyenoic 

Scorpion fish Turbot Red mullet Whiting Pickerel 

As mentioned earlier, the polyenoic fatty acids from marine fish are mostly from the linolenic series (m3). These are eicosopentaenoic (C20 5o 3) and docosohexaenoic (C22 6o 3) acids, the latter usually being the more abundant. Yakovleva (1969) reported that in Black Sea fish die ratio between fatty acids of the 3 and 6 series also displayed a close correlation with the natural mobility levels. 

---

The divergence of plastic metabolism between mobile and sluggish fish can also be found in other animals, including marine invertebrates, with similar structural-metabolic changes underlying it. A comparison between large taxa of molluscs, cephalopods and lamellibranchs, in particular, reveals that their content of docosohexaenoic acid is directly proportional to their degree of mobility. 

The two alternative strategies of metabolism explored in active and sluggish fish therefore apply both to the divergence of energy metabolism and to the closely associated plastic metabolism, which provides normal functioning of energy transformation mechanisms. Active fish are characterized by more... 

In the present context, the data referring to daily variations in the ratio between energy and plastic metabolism are of special interest. It has been found that the processes of energy catabolism predominate in the daytime, while duplication and replication of DNA and protein synthesis dominate... 

This integrated approach differs from the traditional one whereby energy and substance balances were studied separately. Attempts to combine the two most often come down to the study of energy balance with elements of plastic metabolism included, disregarding the balance between different biochemical substrates. Only some studies on marine fish include energy and substance... 

Enriching the water with mineral additives greatly promotes the growth of fish fry (Karzinkin, 1962 Romanenko et al., 1980,1982). Being incorporated into organic compounds, these substances stimulate plastic metabolism. 

Sergeeva, N.T. (1985). Effect of imbalance of fatty acid and amino acid composition of food on lipid metabolism in rainbow trout (In Russian). In Plastic Metabolism in Fish , pp.15-21, Kaliningrad. 

---