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C. B. COWEY AND J. R. SAROENT
present in fish. This pathway is especially important in fish because
the lipid content of natural fish diets usually exceeds the carbohydrate content.
As in land animals, triglycerides provide the bulk of fatty acids for
oxidation in fish, although alkyl diacyl glycerols and wax esters, where
present, will also be utilized. The other lipid classes are not known to
serve generally as energy sources other than in conditions of prolonged
starvation. Thus Olley (1961) and Wilkins (1967) have shown that
phospholipids are mobilized after starvation in the cod and herring
respectively. A special situation, however, may apply during spawning.
Thus it is known that the vascular system in Salmo gairdneri becomes
degenerate at this time, the degeneration being reversed afterwards
(Van Citters and Watson, 1968). Degeneration of this type reflects a
situation where extreme demands are being made on the metabolism
of the fish.
A major difference between fish and land animals, however, lies
in the manner in which lipids and especially triglycerides are stored as
an energy reserve. Thus, as mentioned earlier, many fish do not
possess an adipose tissue in the mammalian sense, but instead store
very large quantities of lipid in their livers and muscles. It may be
mentioned here that the terms “ oil ” and “ fat ” are frequently used
in fish biochemistry to describe essentially triglyceride from depots,
e.g. liver oil, while the term ‘‘ lipid ” usually implies an efficient solvent
extraction so that polar lipids are also included (Bligh and Dyer, 1959;
Lovern, 1965; Ackman, 1967). Table X describes the oil contents of
the livers and muscles of various species of fish where the roles of
adipose tissue and liver, or adipose tissue and muscle, appear to be
combined into a single tissue. Such tissues are referred to as adiposite
liver and adiposite muscle. The lipid in such tissues is known as depot
fat. In noting that adiposite liver and adiposite muscle are relatively
common in fish it should not be forgotten that many species including
ling cod, red cod, black cod, some soles and flounders and salmon, store
relatively large quantities of lipids in the tissues of the intestine and
mesentery, as well as in adiposite tissue (Brody, 1965). The site of
normal lipid storage in fish is significant from the viewpoint of the
nutritional status of fish, as well as in understanding the overall
energetics.
The second major role of lipids in animals, that of maintaining the
structures and functions of biomembranes, is no less important to the
well-being of the fish than that of energy provision. While the triglycerides feature very largely in energy provision, it is the polar lipids
together with cholesterol and its esters that feature largely in bio-
C. B. COWEY AND J. R. SAROENT
present in fish. This pathway is especially important in fish because
the lipid content of natural fish diets usually exceeds the carbohydrate content.
As in land animals, triglycerides provide the bulk of fatty acids for
oxidation in fish, although alkyl diacyl glycerols and wax esters, where
present, will also be utilized. The other lipid classes are not known to
serve generally as energy sources other than in conditions of prolonged
starvation. Thus Olley (1961) and Wilkins (1967) have shown that
phospholipids are mobilized after starvation in the cod and herring
respectively. A special situation, however, may apply during spawning.
Thus it is known that the vascular system in Salmo gairdneri becomes
degenerate at this time, the degeneration being reversed afterwards
(Van Citters and Watson, 1968). Degeneration of this type reflects a
situation where extreme demands are being made on the metabolism
of the fish.
A major difference between fish and land animals, however, lies
in the manner in which lipids and especially triglycerides are stored as
an energy reserve. Thus, as mentioned earlier, many fish do not
possess an adipose tissue in the mammalian sense, but instead store
very large quantities of lipid in their livers and muscles. It may be
mentioned here that the terms “ oil ” and “ fat ” are frequently used
in fish biochemistry to describe essentially triglyceride from depots,
e.g. liver oil, while the term ‘‘ lipid ” usually implies an efficient solvent
extraction so that polar lipids are also included (Bligh and Dyer, 1959;
Lovern, 1965; Ackman, 1967). Table X describes the oil contents of
the livers and muscles of various species of fish where the roles of
adipose tissue and liver, or adipose tissue and muscle, appear to be
combined into a single tissue. Such tissues are referred to as adiposite
liver and adiposite muscle. The lipid in such tissues is known as depot
fat. In noting that adiposite liver and adiposite muscle are relatively
common in fish it should not be forgotten that many species including
ling cod, red cod, black cod, some soles and flounders and salmon, store
relatively large quantities of lipids in the tissues of the intestine and
mesentery, as well as in adiposite tissue (Brody, 1965). The site of
normal lipid storage in fish is significant from the viewpoint of the
nutritional status of fish, as well as in understanding the overall
energetics.
The second major role of lipids in animals, that of maintaining the
structures and functions of biomembranes, is no less important to the
well-being of the fish than that of energy provision. While the triglycerides feature very largely in energy provision, it is the polar lipids
together with cholesterol and its esters that feature largely in bio-