6 



JAMES W. ATZ 



tivity is responsible for this, the forerun- 

 ner of a series of profound changes that 

 are brought about in stored sea water by 

 bacteria. Although the sea contains a 

 widely distributed microscopic fauna and 

 flora consisting of protozoans, algae, fungi, 

 yeasts, and bacteria, only bacteria have as 

 yet been found to be important in sea 

 water maintained in vessels or water sys- 

 tems (ZoBell, 1946, 1959; Harvey, 1955). 

 A^^ien fresh, filtered sea water is stored, 

 there is a tremendous increase in the num- 

 ber of bacteria, a maximum population of 

 from 2 million to 100 million per cc, being 

 attained in 3 to 6 days at room tempera- 

 ture (ZoBell and Anderson, 1936). In 

 about 2 weeks the initial growth phase is 

 over, and the population then fluctuates 

 from a few thousand to more than 100,000 

 per cc. At the same time, the number of 

 species of bacteria is drastically reduced 

 to less than half a dozen. Sea water 

 stored for 4 years at 2° to 6° C. still con- 

 tained more than 200,000 bacteria per cc. 

 (ZoBell and Anderson, 1936), while that 

 vStored at room temperature became prac- 

 tically sterile in 6 months (MacGinitie, 

 personal communication). 



During the period of the precipitous 

 growth and decline in number of bac- 

 teria and for some time thereafter, stored 

 sea water is lethal to the more delicate 

 creatures reared in marine laboratories 

 (MacGinitie, 1947). Because of similar 

 difficulties, aquarists using natural sea 

 water in small aquariums (up to about 100 

 gallons) subscribe to the procedure of 

 storing the water in glass in the dark for 

 6 weeks before use. The lethal effect ap- 

 pears to result from the presence of bac- 

 terial metabolites, since aeration is not 

 supposed to relieve the condition. In con- 

 trast, public aquariums have neA^er re- 

 ported any difficulties with fresh sea water, 

 perhaps because of the much greater vol- 

 umes of water, more effective filtration, 

 and lack of delicate forms in their 

 establishments. 



The control of bacteria must be one of 

 the principal objectives in the manage- 

 ment of salt-water systems and aquariums, 

 but so little is known about the forms that 

 occur in these artificial habitats that any 

 approach is largely empirical. Although 

 sea water has well-recognized bactericidal 

 effects, it also provides an excellent 

 medium for some bacteria, and when en- 

 riched with organic matter, may contain 

 billions per cc. These microorganisms can 

 reduce the amount of dissolved oxygen. 

 They can also produce asphyxiating 

 amounts of carbon dioxide and in this way, 

 as well as others, may dangerously lower 

 the pH. Under anaerobic conditions, 

 they produce methane and hydrogen sul- 

 phide, the latter of which is known to be 

 strongly toxic to fish (Doudoroff and 

 Katz, 1950). Quite possibly they pro- 

 duce metabolites that are inimical to 

 higher forms. Although this has never 

 been demonstrated, Harvey (1925) found 

 that sea water in which a worm had putri- 

 fied or to which enough peptone had been 

 added to make it become cloudy was toxic 

 to a species of copepod for some days, even 

 after it had been filtered through a Berk- 

 feldt candle several times and also well 

 aerated. 



A sine qua non of bacterial control in 

 confined bodies of sea water is cleanliness, 

 achieved by avoiding overfeeding and 

 overcrowding and by practicing sys- 

 tematic but not stereotyped cleaning pro- 

 cedures. In addition, four methods of 

 reducing the number of bacteria have been 

 used, viz., filtration, storage in the dark, 

 ultraviolet treatment, and addition of 

 antibiotics. The efficacy of filtration and 

 storage had been well known long before- 

 Stowell and Clancey (1927) found, at the 

 London Aquarium, that storage in the 

 dark for 28 days eliminated '■'■^^ per cent, 

 of the ordinary bacteria and 97 per cent, 

 of the so-called 'blood-heat' organisms and 

 bacteria of the human intestinal type," 



