WATER MANAGEMENT FOR MARINE AQUARIUMS 



9 



teinaceous substances causes an increase in 

 the pH of sea water, while bacterial oxi- 

 dation of ammonia to nitrite or nitrate 

 causes a decrease (ZoBell, 1959). These 



relationships require consideration, for 

 Saeki (1958) has reported that a low pH 

 inhibits the oxidation of ammonia in 

 aquariums. 



DISSOLVED RESPIRATORY GASES 



Sea water can dissolve about 20 percent 

 less oxygen than fresh water; at 20° C, 

 for example, oxygen-saturated sea water 

 (salinity 36 parts per thousand) contains 

 7.12 p.p.m. of that gas, as compared with 

 8.84 for distilled water (Truesdale, Down- 

 ing, and Lowden, 1955). A survey of the 

 literature has shown that the minimum 

 oxygen requirements of marine fishes 

 range from 3.3 to 0.1 p.p.m. At the Lon- 

 don and Plymouth aquariums. Brown 

 (1929) found that the sea-water systems 

 were 60 to 90 percent saturated with oxy- 

 gen. No temperatures are given, but at 

 20° C, this would correspond to at least 

 4 p.p.m,, and at 30° C, to 3.6 p.p.m., which 

 may be considered adequate for the ma- 

 jority of fishes. 



The carbon dioxide content of sea water 

 influences the respiration of fish by reduc- 

 ing the amount of oxygen carried by their 

 red blood corpuscles (Fry, 1957). This is 

 also a pH effect, and it would therefore be 

 expected that sea water whose pH was 

 low — whether from an accumulation of 

 carbon dioxide or a loss of alkali reserve — 

 would inflict respiratory stress on various 

 fishes. Although general aquarium exper- 

 ience bears this out, no experiments to 

 demonstrate the phenomenon have ever 

 been reported. A pH of 7.8 or more ap- 

 pears to be safe for all fishes, while one of 

 7.0, or even 6.8, is adequate for some of 

 them (Oliver, 1957) . One important char- 

 acteristic of carbon dioxide and its passage 



between the sea and the atmosphere is that 

 the process takes place relatively slowly, 

 and even with artificial aeration may re- 

 quire several hours (Harvey, 1928, 1955). 



Marine fishes that are exposed to sea 

 water supersaturated with air frequently 

 develop gas-bubble disease in which bub- 

 bles, mostly of nitrogen, appear under the 

 skin, especially on the fins, and within 

 various vital organs, causing exophthal- 

 mia, loss of equilibrium, and death. 

 The supersaturation generally results 

 from a leaky pump or pipeline which per- 

 mits air to enter and mix with water that 

 is put under pressure, or from a sudden, 

 relatively great increase in water tempera- 

 ture. Marsh and Gorham (1905) first de- 

 scribed the disease and its cause in detail, 

 and their account was based on its occur- 

 rence in fishes living in a sea-water cir- 

 culatory system. Since then, all investi- 

 gations appear to have been carried out 

 on fresh- water species (Harvey and 

 Smith, 1961). Dr. Eoss F. Nigrelli, 

 Pathologist of the New York Aquarium, 

 has suggested that denitrifying bacteria 

 may be a source of nitrogen that causes 

 gas-bubble disease. 



For the aquarist or experimentalist with 

 a physicochemical background, the pa- 

 pers by Downing and Truesdale (1955, 

 1956) and Haney (1954) provide basic 

 and theoretical data on the aeration of 

 aquariums. 



MARINE CIRCULATORY SYSTEMS 



From the preceding account, there can relations between captive marine macro- 

 be little doubt of the complexity of inter- and micro-organisms and the sea water 



