Fig. 5. Mantle muscle trimethylamine oxide (TMAO) content (mmol kg–1; squares) increases (b=0.33) in proportion to digestive gland mass (% body mass; circles; b=0.25) and lipid mass (% body mass; plus signs; b=0.47) through ontogeny (size; g) in gonatid squid (Cephalopoda). The data for TMAO content are from Kelly and Yancey (1999) and B. A. Seibel (unpublished results). Body masses for the TMAO scaling analysis (squares) for Gonatopsis borealis and Berryteuthis magister were estimated at the mean adult body mass for each species (Hayashi, 1989; Hayashi and Yamamoto, 1987). Digestive gland and lipid masses were taken from various sources: Gonatus onyx (B. A. Seibel, personal observation), Gonatus fabricii (Arkhipkin and Bjorke, 1999), Gonatopsis borealis (Hayashi, 1989) and Berryteuthis magister (Hayashi and Yamamoto, 1987). All species appear to fall on the same scaling line despite differences in maximum body sizes. The apparent correlation between lipid content (or digestive gland mass) and TMAO content in gonatid squid is hypothesized to result from the requirement for phosphatidyl choline hydrolysis to produce diacylglycerol for lipid storage. The choline thus released is oxidized to TMAO.
