AN ANNULAR TANK FOR SEA FISHES 



By Allan C. DeLacy, Professor of Fisheries 



University of Washington, Seattle, Wash. 



Abstract. — The College of Fisheries of the University of Washington maintains an 

 8,000-gallon recirculating sea-water system. A 2,000-gallon annular tank has enhanced 

 growth and longevity of certain fish species. Light and temperature control afford 

 flexibility in establishing artificial environments. 



The College of Fisheries at the Uni- 

 versity of Washington maintains a recir- 

 culating salt-water system with a total ca- 

 pacity of about 8,000 gallons. Rubber- 

 lined steel pipes, sumps, and storage tanks 

 are prominent features of the system. 

 Twelve rectangular aquariums of concrete 

 and glass, a 2,000-gallon annular tank of 

 rubber-lined steel, and a single 450-gallon 

 fiberglass-lined wooden tank comprise the 

 permanent fish-holding facilities. Addi- 

 tional important features of the system are 

 the sand filters, temperature-control equip- 

 ment, and flexibility which permits the en- 

 tire system to be operated as a unit or 

 allows subdivision into two independent 

 systems, one for cooling and one for warm- 

 ing sea-water as desired. Temperatures 

 commonly fluctuate less than 1° F. from 

 a chosen level. 



The annular tank (fig. 1) has proved 

 to be a feature of particular interest in 

 the College of Fisheries salt-water sys- 

 tem. It is simply a 3-foot-wide annular 

 channel with an outer diameter of 10 feet. 

 A water depth of 4 feet is maintained. 

 Two inlets discharge into the surface at a 

 slight angle thereby producing a weak cir- 

 cular current in the tank. Four evenly 

 spaced surface openings on the inner wall 

 serve as outlets. A bottom outlet is used 

 when the water level is to be lowered. 

 Eight 16-inch-square glass ports in the 



outer wall and four in the inner wall per- 

 mit lateral viewing and photography of 

 contained specimens. 



Active fish cruise around and around in 

 the annular tank making infrequent con- 

 tact with the sides. A fingerling silver 

 salmon {Oncorhynchus kisutch) was 

 reared to maturity (5 pounds) in the tank 

 without experiencing the deformities and 

 damage to the snout which accompany con- 

 finement in the smaller (200-gallon) rec- 

 tangular aquariums. Two ratfish 

 {Hyclrolagus colllei) lived 3 years in the 

 tank and finally died after an operational 

 error which permitted a temporary but 

 severe temperature increase. A skilfish 

 {Erilepis zonifer) introduced to the tank 

 as a 3-pound, 17-inch fish weighed 36 

 pounds and measured 39 inches in total 

 length after 6 years. 



Total water use by all aquariums aver- 

 ages about 20 gallons a minute. Over a 

 period of several months, salinity may 

 fluctuate through a range of 1 part per 

 thousand, and pH may decrease by a half 

 a unit. Frequency of water replacement 

 is related to type and number of orga- 

 nisms being held but in general from one- 

 half to three-quarters of the water in the 

 system is replaced three or four times a 

 year. New water is brought to the cam- 

 pus by wooden barge from nearby Puget 

 Sound. 



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