Pressure Effects on Cholesterol and Lipid Synthesis by the Swimbladder of an Abyssal Coryphaenoides Species

SYNOPSIS. The swimbladder gas gland is recognized as a cholesterol synthesis site in abyssal rattail fishes, Coryphaenoides sp. (from 2000 m depth), and Galapagos Islands surface fish, Orthopristis forbesi, Seriola mazatlana , and Sphoeroides annulatus . This relates to high levels of cholesterol in the gas gland (up to 21% of lipid) and high cholesterol levels in the fatty swimbladder interior (up to 49% of lipid). The gas gland has more protein (45.4%) than the internal fatty mass (18%). Lipids synthesized include phospholipids and triglycerides in 2:1 ratio in the gas gland and 1:2 ratio in the liver. Deep fish have fatty livers (66%) compared to shallow fish (28%). Shallow fish incorporated five times as much acetate-l-14C into lipids as did deep fish, and seven to eight times as much acetate-l-14C into cholesterol. Pressure facilitation of cholesterol synthesis was observed in gas gland and liver of O. forbesi and Coryphaenoides , whereas total lipid synthesis was inhibited by higher pressures. Optimal acetate-l-14C incorporation into lipids occurred at 5000 psi and 2°C in Coryphaenoides ; it occurred at 14.7 psi and 15° in O. forbesi . These conditions closely approximate the environment of the fish.

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