The fatty acid composition of phospholipids and the contents of docosahexaenoic acid (DHA)-containing diacyl phosphatidylcholine and diacyl phosphatidylethanolamine molecular species were determined from brains of five fresh-water fish species from a boreal region adapted to 5°C, five fresh-water fish species from a temperate region acclimated to 5°C, five fresh-water fish species from a temperate region acclimated to 20°C, and three fresh water fish species from a subtropic region adapted to 25-26°C, as well as six mammalian species and seven bird species. There was little difference in DHA levels of fish brains from the different thermal environments; mammalian and bird brain phospholipids contained a few percentage points less DHA than those of the fish investigated. Molecular species of 22:6͞ 22:6, 22:6͞20:5, 22:6͞20:4, 16:0͞22:6, 18:0͞22:6, and 18:1͞22:6 were identified from all brain probes, and 16:0͞22:6, 18:0͞22:6, and 18:1͞22:6 were the dominating species. Cold-water fish brains were rich in 18:1͞22:6 diacyl phosphatidylethanolamine (and, to a lesser degree, in diacyl phosphatidylcholine), and its level decreased with increasing environmental͞body temperature. The ratio of 18:0͞22:6 to 16:0͞22:6 phosphatidylcholine and phosphatidylethanolamine was inversely related to body temperature. Phospholipid vesicles from brains of cold-acclimated fish were more fluid, as assessed by using a 1,6-diphenyl-1,3,5-hexatriene fluorescent probe, than those from bird brains, but the fluidities were almost equal at the respective body temperatures. It is concluded that the relative amounts of these molecular species and their ratios to each other are the major factors contributing to the maintenance of proper fluidity relationships throughout the evolutionary chain as well as helping to maintain important brain functions such as signal transduction and membrane permeability.

Daphnia magna andCyclops strenus were maintained in aquaria containing sodium [1‐14C] acetate and the effect of temperature on labeling of their lipids was investigated. Incorporation of radioactivity in total lipids was slowed by a factor of 4 in cold‐exposed (5C) specimens compared to those incubated at 25 C. There was no significant difference in the distribution of label in the lipid classes of animals incubated at the two extreme temperatures. Decrease of the temperature from 25 to 5 C brought about a considerable reduction in the formation of palmitic and stearic acids and an increase in labeling of monounsaturated (18∶1) fatty acids inD. magna. Docosapolyenoic acids were absent from lipids of this crustacean.C. strenus directed a higher proportion of radioactivity into both oleic and docosahexaenoic acids upon cold exposure. In response to decrease of the temperature,D. magna formed a less unsaturated fatty acid population, as judged from dpm ratios of total saturated to total unsaturated fatty acids, thanC. strenus. Inability to form and accumulate docosapolyenoic fatty acids byD. magna might be related to their poor survival at reduced temperatures.

Phospholipid (PL) composition, fatty acid (FA) composition of total and major individual PL as well as the physical state of isolated PL were investigated in relation to temperature exposure by freshwater planktonic crustaceans,Cyclops vicinus andDaphnia magna. C. vicinus, adapted to warm water, accumulated appreciable amounts of docosahexaenoic acid in its PL within 3 days when the temperature was decreased from 20 C to 10 C. Docosahexaenoic acid was preferentially esterified to phosphatidylethanolamine (PE). Docosapolyenoic FA were absent in PL ofD. magna and this species did not increase polyenoic acid level under identical temperature treatment. The level of PE was elevated, however, in both species in response to decreased environmental temperature. Two characteristic breaks were observed in ln S vs 1/T plots of 5‐doxyl stearic acid spin probs. These were at 19 C and 13 C forC. vicinus and at 20 C and 7 C forD. magna. C. vicinus shifted both the upper and lower phase‐separation temperatures of its PL to lower temperatures when exposed to cold. Differences between the onset and completion of phase‐separation temperatures equalled that in environmental temperature (10 C). The phase‐separation temperatures ofD. magna were unchanged under identical experimental conditions. Results are interpreted as a complete temperature adaptation of membrane transitional state byC. vicinus but not byD. magna. Researchers have postulated that one of the reasons the latter species cannot overwinter in an active form as doesC. vicinus, but instead overwinters as resting eggs, involves its failure to adapt membrane PL composition and physical state to temperature.

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The paper summarises experimental data demonstrating effects of various dietary factors exerting changes in the fatty acid composition and fatty acid metabolism of the common carp (Cyprinus carpio L.). Among the dietary factors (1) supplementary feeding in fish ponds, (2) absence of essential fatty acids (EFA) in the diet, (3) starvation, and (4) ration level were studied. It was concluded that supplementary feeding in carp rearing ponds is frequently excessive in the Hungarian carp culture practice, inducing slight EFA-deficiency and enhancing de novo fatty acid synthesis. This latter caused enlarged fat depots with high oleic acid contents in the fish organs and tissues. EFA-deficient diets enhanced the synthesis of oleic acid except when high rate of de novo fatty acid synthesis was suppressed by dietary fatty acids. Feeding EFA-deficient diets caused gradual decrease in the levels of polyunsaturated fatty acids and gradual increase in that of Mead's acid: 20:3(n-9), an indicator of the EFA-deficiency. At prolonged starvation, polyunsaturated fatty acids of the structural lipids were somehow protected and mainly oleic acid was utilised for energy production. At high ration levels, excessive exogenous polyunsaturates were decomposed, and probably converted to oleic acid or energy. Starvation subsequent to the feeding the fish at various ration levels, reflected adaptive changes in the fatty acid metabolism: Below and above the ration level required for the most efficient feed utilisation for growth, decomposition processes of the fatty acid metabolism were accelerated.