SEA-WATER SYSTEM IN SHELLFISH LABORATORY 



159 



the system, various organisms grow 

 rapidly in the pipes and it is necessary to 

 be able to unscrew the system easily for 

 cleaning. The descending arm of the T- 

 tube is fitted with a rubber bung held in 

 place by a coupling nut. A glass tube is 

 passed through the bung and a piece of 

 rubber tube with a screw clip is fitted on to 

 control the supply to individual aquar- 

 iums. 



It is necessary to hold the tankroom at 

 a constant temperature in order that the 

 rate of cooling in the aquariums shall be 

 constant. The rate of flow is about 10 

 liters per hour into a 40-liter aquarium 

 and, as the system produces water at a 

 constant temperature, variations in the 

 cooling rate can have a considerable effect 

 on a tank. It is such changes that cause 

 the gradual variations in temperature re- 

 corded in figure 2, which are, however, less 

 than those recorded in most natural en- 

 vironments. While equipping each aquar- 

 ium with its own heater, thermostat, and 

 stirrer gives more precise control, the cost 

 is very much greater. The writer has 

 found that such an installation does not 

 give any better results and to have so much 

 equipment in each tank is a nuisance. 



HATCHERY 



The sea water in the hatchery is used 

 for the culture of oyster larvae and for 

 this purpose it needs to be free from sus- 

 pended material and substantially sterile. 



The water is first filtered by pumping 

 through a pressure filter. The pump is a 



%-inch plastic pump with a neoprene im- 

 peller and stainless-steel shaft (Cleghom, 

 Waring & Co. Ltd., St. Albans, Herts.). 

 The pressure filter (Aerox Ltd., Glasgow) 

 contains a cylindrical ceramic filtering ele- 

 ment 10 inches long by 2 inches in diam- 

 eter. The body of the filter is of vulcanite. 

 It is desirable to interpose a coarse filter 

 before the ceramic filter, as the latter can 

 clog rather rapidly, particularly if there 

 is a lot of phytoplankton in the water. 

 After filtration, the water is sterilized by 

 ultraviolet light using a 44-watt low- 

 pressure mercury discharge lamp (Hano- 

 via Ltd., Slough, Bucks.). In this lamp 

 the water circulates between an inner 

 quartz jacket containing the lamp and an 

 outer glass jacket. This pump and filter 

 unit pass about 300 liters per hour, a flow 

 rate at which the ultraviolet lamp is able 

 to kill more than 99 percent of the bacteria. 

 The water is then passed directly via i/^- 

 inch polythene piping and Saunders valves 

 to the larval culture tanks. It is also ad- 

 visable to keep the piping from the ultra- 

 violet lamp to the tanks as short as possi- 

 ble, since bacterial contamination can oc- 

 cur from the wall of the pipe, and bac- 

 teria which multiply on the inside of the 

 pipe form a nucleus for recontamination. 



SUMMARY 



An account is given of a sea-water sup- 

 ply system in a shellfish-culture labora- 

 tory. Provision is made for heating the 

 water to 22° C. and for continuous enrich- 

 ment with algal culture. 



