Sprat lipids

There is a strong interannual variation in the lipid concentration in the flesh of planktivorous fish such as anchovy, kilka and sprat, which is governed by the varying abundance of the plankton (Shulman, 1972b, 1996 Luts and Rogov, 1978 Luts, 1986). 

Figure 34 Lipid accumulation and withdrawal (schematic) in different months by the anchovy and sprat. (After Shulman, 1978a.) Continuous line, sprat broken line, anchovy.

Temperature affects food supply in another way also. The Mediterranean sprat, which prefers cold waters, exploits a wider feeding area than fish that inhabit only warm waters, because it takes advantage of a greater water depth and can feed all the year round. It possesses a much greater lipid reserve than the warm-water anchovy, and its range of fatness over the annual cycle is wider (Figure 36). The feeding conditions in the warm Mediterranean waters are therefore more favourable to fish that prefer cooler waters rather than warm. 

Figure 36 Annual lipid cycle in anchovy (broken line) and sprat (continuous line) in the Mediterranean. (After Shulman, 1978a.)...

Long-term fluctuations in lipid accumulation by Black Sea sprat during the summer post-feeding period, when their fat reserve is at its peak, were observed from 1960 to 1994 and this work continues (Shulman et al.t 1994). Interannual variability in the lipid content, though small, is real, with a coefficient of variation of 12-15%, as estimated at certain points of this period of time. 

Figure 52 Seasonal changes in somatic and generative growth in populations of anchovy and sprat (mg g-1 fresh tissue) solid line, proteins broken line, lipids dotted and broken line, mineral matter and glycogen.

Figure 54 Seasonal changes in the lipid fractions of the white muscle of sprat O, triacyl-glycerols , phospholipids A, cholesterol , non-esterified fatty acids.

The transformation of food is very similar in populations of anchovy and sprat (Figure 66). The total amount of lipid and protein assimilated into the body is also similar in the two species, but their proportions differ between the food and the fish body the food is richer in protein and poorer in lipid when compared with the fish which consume it. Somewhat less than half of the body lipid appears to be formed from ingested protein ( liponeogenesis ), whereas all of the body protein originates in the diet. Some of the dietary lipid and, possibly, protein is transformed into glycogen. The mechanisms responsible... 

Table 19 demonstrates the results of the calculation, using data from Table 11. It can be seen that, depending on the species, from 2% to 24% of the dry food substance is assimilated for the total protein production and 0.7% to 8.0% for the total lipid production. Assuming that protein and lipid are adequately used for the somatic and generative productions, one can make relevant estimates (Table 19). The resulting data of K2 of P of protein and lipid are of especial interest. They indicate the efficient assimilation of nutrients to provide somatic production and accumulation of lipid. The following ratios between food assimilated for protein and lipid production have been obtained for Black Sea fish 2.6 1 in anchovy, 2 1 in sprat, 2.1 1 in horse-mackerel and red mullet, 2.7 1 in pickerel, and 4 1 in whiting.

It should be borne in mind that the lipid index cannot characterize the food supply over the whole annual cycle, but only that in the period when lipids are accumulated rather than consumed. For warm-water fish of the southern European seas, this is the summer and autumn, while for cold-water fish such as the Black Sea and Mediteranean sprat, it is spring and summer. The food... 

The second period ranged from 1978 to 1985. In the first half, the fatness of the sprat showed the highest rise recorded, from comparatively low values to 15.5%, which level persisted for 3 years, followed by a pronounced drop to 9% and later a rise to 12%, the coefficient of variation being 15.2%. The abundance of the stock of sprats changed with the changes in their lipid contents, the stock of 1980 being three times that of any recorded in the period 1960-1977. 

Figure 72 Annual variations in the lipid content of sprat of different sizes. Fish were caught in June or July. (After Minyuk, 1991.)...

In fatty fish, the total lipid content correlates negatively with the content of dry matter and water. The fat-water line has been recognized in dozens of species of fish (Kizevetter, 1942 Levanidov, 1950 Luhmann, 1953, 1955 Brandes and Dietrich, 1958 Krivobok and Tarkovskaya, 1960 Shulman, 1961). The correlation is a good one (r=-0.8 to -0.9), but each species has its own equation. In Black Sea sprat, for example, the relationship is Y=-13.28 + 0.84X, where Y is the total lipid content and X the content of dry matter... 

In northern seas, fish such as herring, cod, haddock and flounder show intraspecies population differences in life span, structure, age at maturity and various physiological and biochemical characteristics (Shatunovsky, 1963, 1970 Love, 1970,1980 Storozhuk, 1971 Lapin, 1973). In contrast, fish from the Black, Azov and Mediterranean Seas have shorter life spans and display less distinct intraspecifc differences. Moreover, within one sea population, fish of one species do not differ much in age structure, fecundity or spawning character. The most pronounced difference in the latter group of species is the rate of lipid accumulation in sprat from different sites in the Black Sea and anchovy in the Azov Sea (Shulman, 1972b). Comparison of anchovy from the Azov, Black and Mediterranean Seas shows more marked differences in the levels of accumulated lipid and the growth rate (Chapter 2). 

Minyuk, G.S., Shulman, G.E., Shchepkin, V.Ya. and Yuneva, T.V. (1997). Black Sea sprat the Relationship between Lipid Dynamics, Biology and Fishery (In Russian). EKOSI-Hydtophysica, Sevastopol, 139 pp. 

Yuneva, T.V. (1990). Seasonal dynamics of the fatty acid content of lipids in Black Sea anchovy and sprat (In Russian). In Bioenergetics of Aquatic Organisms (G.E. Shulman and G.A. Finenko, eds), pp. 196-207, Naukova Dumka, Kiev. 

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