Ammonia uptake coefficient

The ratio of oxygen uptake to ammonia excretion in Black Sea mussels has been found to exhibit a distinct daily rhythm (Slatina, 1986). As a rule, the ammonia coefficient (O/N) tends to increase greatly at night. As this rise in energy metabolism does not result from an enhanced locomotor activity, it is difficult to explain or to find any analogue in fish. Farbridge and Leatherland (1987) demonstrated a strong effect of the lunar cycles on amino acid uptake by the scales, also on nucleic acids, metabolic reserves and plasma thyroid hormones in coho salmon. 

Indicators related to nitrogenous metabolism include the concentrations of free amino acids (Shcherbina, 1973 Ostroumova, 1983). The ammonia coefficient (O/N), described in Chapter 2, is also useful, values less than 8.67 indicating anaerobic metabolism which can be caused by, for example, increased concentrations of heavy metals in the water, which inhibit the normal supply of oxygen to the tissues (Shulman, 1996). The rate of oxygen uptake is by itself a good indicator of condition, responding as it does to every disturbance of the norm (Stroganov, 1968). 

The influence of moderators upon diffusion coefficients is shown in Figure 13 for mordenite moderated with ammonia for a number of diffusing species. Da may change by orders of magnitude for relatively small amounts of modifier. This can result in cut-offs in the amounts sorbed, on the time scale of normal experiments, which occur at different uptakes of NH3 for molecules of different dimensions. Different moderator molecules can, molecule for molecule, have different effects upon the diffusion coefiicients. These effects tend to follow the sequence of the molecular volumes of the moderator. As the amount of moderator increases, the energies of activation for diffusion increase (Table X), to parallel the decrease in Da. 

Fig. 1. Three-dimensional representation of effects of varying electron allocation coefficient (EAC) and uptake hydrogenase activity (Hup) on respiratory costs of ammonia synthesis fixation of molecular nitrogen (see text for assumptions used and basis of calculation of costs).

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