layer of vinyl. The 500-gal storage tank is con- 

 structed of spun fiber glass. 



An open floor drain, leading from the lab- 

 oratory into a storm drain, is used for disposing 

 water from the experimental tanks and water 

 tables, and for emptying the pool-reservoir. 



During experiments the pool and water 

 tables are enclosed by opaque curtains that run 

 on ceiling-mounted tracks. 



Numerous grounded electrical outlets are 

 located about the laboratory and along the 

 raised ceiling above the catwalk. Fluorescent 

 lights are mounted above the water tables and 

 the rectangular experimental tank. 



A reverse-cycle air-conditioning unit is used 

 to maintain the laboratory and the recirculated 

 water at a constant temperature. 



Operation of the recirculation system can 

 best be understood by following the water flow 

 through its various components. 



Water from either the saltwater well or from 

 the high-salinity wedge is aereated by splash- 

 ing into the 500-gal storage tank. When the 

 tank is full, water is then pumiced from the 

 storage tank through the diatomaceous-earth 

 filter and splashed back into the storage tank. 



Upon completion of the cleaning procedure, 

 each 500-gal batch of water is pumped up to 

 a filter box from where it enters the pool- res- 

 ervoir. Cleaning is repeated until the recircu- 

 lation system is full. At that time, the storage 

 tank and diatomaceous-earth filter are isolated 

 from the basic recirculation system. 



Water in the recirculation system flows from 

 the pool into the sump as the hydrostatic pres- 

 sure balance between these two components is 

 disrupted following the pumping of water out 

 of the sump. Water from the sump is pumped 

 up to an elevated filter box (only one filter box 

 is used at a time) where it is aereated by splash- 

 ing onto the oyster-shell filter material. 

 Crushed oyster shells were used for recondi- 

 tioning the salt water. A concise discussion 

 of water reconditioning and the function of 

 oyster shells is given by Burrows and Combs 

 ( 1968) . Water percolating through the crushed 

 shells is collected by perforated pipes, in the 

 bottom of the filter box, which lead into the 

 distribution system. The water is then re- 

 turned to the pool-reservoir, or directed to the 

 experimental tanks, or to the water tables. 



During experiments the pool can be isolated 

 from the recirculation system by directing 

 water into the sump and closing the connecting 

 line between pool and sump. 



The delivery rate of the gravity flow system 

 was limited primarily by the percolation rate 

 through the filter. A maximum flow rate, esti- 

 mated at about 20 gal/min, was obtained when 

 full hydrostatic pressure in the filter boxes was 

 maintained by continuous overflowing excess 

 water back into the sump. 



The recirculation system described has func- 

 tioned satisfactorily, within its limitations, and 

 has proved adequate for maintaining a modest 

 saltwater experimental facility. 



ACKNOWLEDGMENTS 



Brandy Siebenaler (Gulfarium, Ft. Walton 

 Beach, Fl.) helped solve some of the problems 

 encountered in the design and operation of the 

 system. Kenneth Marvin (NMFS Biological 

 Laboratory, Galveston, Texas) suggested the 

 use of crushed oyster shells as a filter medium. 

 Personnel of the NMFS Technological Labora- 

 tory, Pascagoula, Miss., tested water samples 

 from the recirculation system and saltwater 

 well. Special thanks are due Edward F. Klima 

 (NMFS Exploratory Fishing and Gear Re- 

 search Base, Pascagoula, Miss.) for his encour- 

 agement and assistance during construction of 

 the saltwater laboratory. 



LITERATURE CITED 



BURROWS, R. E., and B. D. COMBS. 



1968. Controlled environments for salmon propa- 

 Ration. Progr. Fish-Cult., .30: 123-136. 

 CLARK, J. R., and L. CLARK (Editors). 



1964. Sea-water systems for experimental aquar- 

 iums. A collection of papers. U.S. Fish Wildl. 

 Serv., Res. Rep. 63, 192 p. 

 MARVIN, K. T., and R. R. PROCTOR, JR. 



196.5. Description of salt-water laboratories. In 

 Biological Laboratory, Galveston, Texas, fish- 

 ery research for the year ending June 30, 

 1964. U.S. Fish Wildl. Serv., Circ. 230, p. 

 94-102. 

 MARVIN, K. T., and R. S. WHEELER. 



1961. Sea-water system. In Galveston Biological 

 Laboratory, fishery research for the year end- 

 ing June 30, 1961. U.S. Pish Wildl. Serv., 

 Circ. 129, p. 68-71. 



GPO 998-779 



