A FAST-FLOW CLOSED-CIRCUIT MARINE AQUARIUM 



By L. J. Hale 



The Asfiworth Laboratory, University of Edinburgh, Edinburgh, Scotland 



Abstract. — A relatively fast flow of sea water results in a much greater success in 

 keping marine organisms in aquariums, and a closed-circuit system will remain biologi- 

 cally balanced without changing or filtering the sea water and without temperature 

 control. The water is actively circulated by a special pump which is an elaboration of 

 the bubbling tube. This pump has advantages over conventional pumps in the absence 

 of corrosion and contamination and of damage to organisms passing through it; it 

 requires little maintenance. 



In earlier papers (Hale, 1957, 1960a) I 

 briefly described closed-circuit experi- 

 mental aquariums which probably owed 

 their success primarily to the relatively 

 fast circulation of the sea-water. There 

 were neither filters nor reserve tanks in 

 the system; the water was never changed 

 nor its temperature controlled. From the 

 experience so gained a permanent ap- 

 paratus was built and has been operated 

 successfully for over 4 years. The details 

 of this aquarium are described in this 

 paper. 



ECOLOGICAL CONSIDERATIONS 



The essential features of this aquarium 

 are based on possible changes in the 

 aquarium water, and how these changes 

 might be counteracted by providing an 

 adequate flow of water. These considera- 

 tions will be discussed briefly. 



Inorganic Ions 



The greatest problems encountered with 

 sea-water aquariums arise from changes 

 in the concentration of ions which occur 

 in the artificial environment. These 

 changes are caused by the contained orga- 

 nisms, and any radical departure from 

 normal is likely to be detrimental. Im- 

 portant among these ions is calcium. The 



concentration of this ion is likely to be 

 rapidly reduced by the many organisms 

 processing calcareous skeletons; they ac- 

 tively remove calcium from the sea water 

 (Bevelander, 1952; Robertson, 1941; Wil- 

 bur and Jodrey, 1952). A decrease in the 

 calcium ion concentration might also take 

 place if the carbon dioxide tension were 

 reduced by too much photosynthesis 

 (Harvey, 1957), and also if the sulphate 

 ion concentration rose as a result of aerobic 

 putrefaction of excessive protein sulphur 

 from dead organisms. Replacement of 

 calcium is likely to take place if an excess 

 of calcium carbonate is kept in the water, 

 such as mollusk shells or limestone chips. 

 It is also clearly an advantage for the pH 

 of the sea water to be kept normal (8.1- 

 8.2) by providing light for an adequate 

 degree of photosynthesis. Photosynthetic 

 plants are also desirable to control inor- 

 ganic nitrogen. 



The concentration of ions containing 

 nitrogen is likely to increase considerably 

 over the minute amounts contained in the 

 sea (Oliver, 1957). Ammonia is excreted 

 by many marine animals; the excretory 

 urea of some will be rapidly hydrolyzed 

 to ammonia. Ammonia is oxidized by 

 nitrifying bacteria to nitrite and then to 



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