8 



JAMES W. ATZ 



lime (CafOH).) is periodically added to 

 the reservoir (Brown, 1929; Atkins, 

 1931; Wilson, 1952, 1960). At the New 

 York Aquarium, sodium bicarbonate 

 (NaHCOs) was added continuously to the 

 circulating water (Breder and Howley, 

 1931), and modifications of this procedure 

 have been used by other aquariums in- 

 cluding the John G. Shedd Aquarium 

 and the London Aquarium. At the 

 Amsterdam, London, ITeno, and New York 

 Aquariums, quantities of some form of 

 calcium carbonate (CaCO,-,) such as bi- 

 valve shells, marble chips, coral sand, or 

 calcite, are kept in contact with the cir- 

 culating water (Sunier, 1951; Oliver, 

 1957; Saeki, 1958), The relative merits 

 of treatment with slaked lime or sodium 

 bicarbonate were briefly argued by Breder 

 and Howley (1931), Atkins (1931), 

 Breder and Smith (1932), and Cooper 

 (1932). One noteworthy aspect of this is 

 the great importance that Breder (1934) 

 attributed to the calcium ion in keeping 

 captive marine fishes. 



Although there are differences of opin- 

 ion whether ammonia is the characteristic 

 excretory product of aquatic organisms 

 (Smith, 1953), it is agreed that this sub- 

 stance is at least one of the principal waste 

 products of fish and aquatic invertebrates. 

 It is also the main nitrogenous substance 

 resulting from the bacterial decomposition 

 of plant and animal tissues under both 

 aerobic and anaerobic conditions in sea 

 water (ZoBell, 1959). Since ammonia is 

 highly toxic to fish in fresh waters, par- 

 ticularly alkaline ones (Doudoroff and 

 Katz, 1950), and there is every reason to 

 believe that it is comparably toxic in sea 

 water, the fate of this metabolite is of con- 

 siderable concern to the marine aquarist. 

 Some ammonia passes into the atmos- 

 phere; the remainder, which is undoubted- 

 ly the bulk of it, is oxidized by bacteria 

 to nitrites and nitrates. Large numbers 

 of these bacteria are found in aquarium 



filters, but some also live on the walls of 

 the tanks (Saeki, 1958) . In a quantitative 

 experiment concerning the nitrogenous 

 substances in closed sea- water circulations, 

 Saeki (1958) found that about 25 percent 

 of the decrease in ammonia resulted from 

 oxidation in the filter by its Schtnutzdeche. 

 Storage of aquarium water in the dark also 

 reduces its ammonia content (Stowell, 

 1926b). The latter may be the result of 

 direct chemical oxidation as well as biotic 

 activity (Harvey, 1955; Vaccaro, 1962). 

 There are bacteria that reduce nitrates and 

 nitrites to nitrogen and others that reduce 

 nitrates to nitrites, but what significant 

 part, if any, they play in the nitrogen cycle 

 of aquariums is unknown. 



In fresh water, nitrates are hardly more 

 toxic to fish than chlorides (Trama, 1954), 

 and no adverse effects on marine species 

 have ever been reported. According to 

 Oliver (1957), however, nitrate can inter- 

 fere with the respiratory processes of some 

 animals, in particular marine inverte- 

 brates. Effects of nitrite do not ever seem 

 to have been described. Oliver (1957) has 

 pointed out that there is no chemical way 

 of removing nitrate, and to accomplish 

 this some adaptation of the denitrifying 

 activities of bacteria appears to offer the 

 most promise. Indeed, Honig (1934) was 

 able practically to eliminate nitrite and 

 nitrate in an experimental marine system 

 by encouraging the multiplication of de- 

 nitrifying bacteria, but Sunier (1951) re- 

 ported that the practical application of her 

 method presented difficulties. In a 6,600- 

 gallon sea-water system at the Wuppertal 

 zoological gardens, the combination of fil- 

 tration by a pressure filter charged with 

 activated carbon and a specially encour- 

 aged growth of marine algae kept nitrite 

 and nitrate concentrations within the 

 range of natural sea water (Seiffge, 1941), 

 The reduction of nitrate and nitrite to 

 ammonia and the formation of ammonia 

 from bacterial decomposition of pro- 



