YANCEY, P.H.*; SAMEROTTE, A.L.; BRAND, G.L.; DRAZEN, J.C.; Whitman College; Whitman College; Whitman College; University of Hawai’i: Increasing contents of TMAO with depth within species as well as among species of teleost fish
Marine teleost fish are generally classified as hypo-osmotic osmoregulators, with internal osmotic pressures of about 300-400 mOsm (compared to seawater at about 1000 mOsm). Thus there is little use of organic osmolytes; shallow-water teleosts typically have only about 40-50 mmol/kg TMAO (trimethylamine oxide), a common osmolyte in many other marine animals. However, previously we reported that both internal osmotic pressure and muscle TMAO contents increase linearly with depth in several families of teleosts. Initial studies compared different gadid, macrourid, morid, zoarcid, and scorpaenid species from 0, 1.9 and 2.9 km depth, with fish from 2.9 km having TMAO at about 180 mmol/kg wet wt. We also showed that TMAO can counteract the effects of hydrostatic pressure on proteins, which may explain the depth trend. We have now analyzed muscles of 15 species of gadids, macrourids, morids, pleuronectids, scorpaenids, and anoplopomatids from 0 to 4.8 km depths. For all data points, 3 to 5 fish were analyzed and standard deviations were 3 to 15 % of the mean. Between 0 and 1 km depth, there is an apparent sigmoidal increase in TMAO contents, from 45 to 120 mmol/kg wet wt. This fits the effects of pressure on biological systems: pressure generally has significant effects only above 100 atm (1 km equivalent). From 1 to 4.8 km, the increase is highly linear (0.99 correlation coefficient), rising to 261 mmol/kg at 4.8 km. This also fits the effects of pressure at higher levels. The trend was found not only among different species, but also within species: in every case in which a species was caught at two or more depths, TMAO was always significantly higher in the deeper-caught specimens. For example, in the macrourid grenadier Coryphaenoides armatus from 2.9, 4.1 and 4.8 km, TMAO contents were 179, 229 and 261 mmol/kg, respectively.
