Metabolism and chemical composition of small teleost fishes from tropical inshore waters

Rates of oxygen consumption (R) and ammonia excretion (E) of 29 species of small teleost fishes, which weighed between 1 and 400 mg dry mass (DM), from inshore waters of the Great Barrier Reef were determined at in situ temperatures (25 to 30°C). Regression analyses revealed that R (6.7 to 1296 µl O2 ind. -1 h -1 ) and E (0.28 to 64.2 µg NH4-N ind. -1 h -1 ) were correlated with body mass, but the ratio of R to E ( oxygen to nitrogen ratio; 17 to 104 by atoms), was not. Water content of fish bodies ranged from 66.0 to 81.4% of wet mass (WM), and ash content from 11.9 to 28.6% of DM. Total carbon (C) and total nitrogen (N) composition varied from 36.2 to 44.4% and from 8.3 to 12.8% of DM, respectively, resulting in C:N ratios of 3.1 to 4.7. Fractions of inorganic C and N were small (0.04 to 0.33% and 0.01 to 0.15% of DM, respectively). Combining R and E data with those of body C and N composition, daily metabolic losses were estimated to be 4.3 to 18.6% for body C and 0.8 to 9.1% for body N. The present R-body mass relationships were compared with the 3 published predictive mod- els for fishes to explore the best fit model. On a body mass basis expressed by N, values for R were consistent with the model for epipelagic zooplankton, but values for E were 30% lower, suggesting somewhat reduced E relative to R in fishes as compared with zooplankton. Three out of the 29 fishes exhibited markedly high metabolic O:N ratios together with high body C:N ratios, which was inter- preted as an adaptation to N-limited detritus nutrition.