Organic reserves in the midgut gland and fat body of the giant deep-sea isopod Bathynomus giganteus
The giant deep-sea isopod Bathynomus giganteus is common in deep waters of the Gulf of Mexico. Isopods store organic reserves both in the midgut gland and in adipocytes (collectively called the "fat body") that are found throughout the body. There is little information about isopod adipose tissue in general or about the organic reserves of B. giganteus in particular. Hence, biochemical composition (lipid, protein, carbohydrate, ash) of the midgut gland and the fat body was determined for this species. Water content was 68% and 78% for the midgut gland and fat body, respectively. On a dry weight basis, the midgut gland was 49.1% lipid, 34.2% protein, 4.8% carbohydrate, and 12.0% ash, whereas the fat body was 56.4% lipid, 29.0% protein, 2.8% carbohydrate, and 11.7% ash. The lipid : protein ratio for the fat body was 2.2:1, whereas it was 1.7:1 for the midgut gland. The most abundant lipid classes in the midgut gland were triacylglycerols (67%), sterol esters (14%), and polar lipids (9%); monoacylglycerols, free fatty acids, cholesterol, and diacylglycerols each contributed from similar to 5% to <1% of the total lipid. The most abundant lipid class in the fat body was triacylglycerols, comprising 88% of the total lipids; the other lipid classes each contributed from similar to 3% to <1%. Wax esters did not occur in this species.